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MyDeficiencies

Primidone

Barbiturates and derivatives, antiepileptics

Also sold as Mysoline.

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Findings for this medication

Research about this medication, graded for how strongly each finding can be attributed to it. Nothing here describes your own levels.

Primidone has real classical-nutrient depletion machinery, and it is the best-documented kind: hepatic cytochrome P450 induction. Primidone is itself metabolized to two active compounds, phenobarbital and phenylethylmalonamide (PEMA), so a patient on primidone is pharmacologically also exposed to phenobarbital, a long-established enzyme inducer. This is disclosed here as a direct metabolite relationship, not a distant class extrapolation: where phenobarbital-specific pharmacology is cited below, it is because primidone converts substantially to phenobarbital in vivo, not because the two drugs merely share a class label. The strongest, most drug-specific signal is folate: primidone has its own named case literature (Chanarin et al., 1958) and its own biochemical mechanism study (Baker et al., 1962) documenting megaloblastic anemia from impaired folate metabolism, corroborated by primidone's own FDA label, which calls the anemia a rare idiosyncratic reaction that resolves with folic acid. Vitamin D and vitamin K show real but bounded signals: controlled trials from the 1970s (Christiansen et al.) found reduced bone mineral content and biochemical osteomalacia in anticonvulsant-treated epileptic patients whose drug regimens included primidone alongside phenytoin and phenobarbital, and a small primidone-containing pediatric case series (Solomon et al., 1977) found reversible depression of vitamin K-dependent clotting factors. Both are bounded because the historical cohorts mixed several enzyme-inducing drugs together, so primidone's individual contribution cannot be isolated, and because a larger, more recent prospective cohort (Kaaja et al., 2002) that specifically broke out primidone-exposed pregnancies found no statistically significant excess of neonatal bleeding from enzyme-inducing antiepileptic drugs as a group. A commonly circulating consumer framing, that anticonvulsants cause a primary dietary calcium deficiency, fails verification: the drug's own controlled-trial data found serum calcium and magnesium unchanged despite the real bone and seizure-threshold effects of vitamin D supplementation, which points to accelerated hepatic catabolism of vitamin D (and a secondary calcium-PTH-bone disturbance), not a direct calcium depletion.

Barbiturates and derivatives, antiepileptics · ATC N03AA03 · also sold as Mysoline · reviewed 2026-10-02. This describes research about the medication. It does not say anything about your own levels or health.

How to read the evidence grades

These colours describe how strongly a finding can be attributed to the medication in the research. They are not a severity score and they say nothing about your own health.

Grades describe how strongly a finding can be attributed to Primidone in the research — not how common it is, how serious it would be, and not anything about you personally.

Red — Severe
Two or more independent Tier A sources, this drug in the cohort, the nutrient directly measured, consistent direction, clinically meaningful magnitude, a named mechanism, no substantial contradicting Tier A evidence.
Orange — Moderate
At least one Tier A source with this drug in the cohort showing a real but bounded deficit: an exposure window, a subgroup, low frequency, or a functional rather than circulating deficit.
Yellow — Low
Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction.
Not graded — disclosed evidence gap
Nothing has been measured here, so this finding cannot be graded. That does not establish either safety or harm, and it is not the same as a White result.Source definition: Not gradeable under the rules above because nothing has been measured. Published as a documented gap, never as reassurance that there is no effect.

What the research found

Folate (vitamin B9)

Red — Severe

See study details

Primidone causes megaloblastic anemia through impaired folate metabolism in a rare but mechanistically well-documented and drug-named subset of patients.

Full detail and limits

What the grade means here: Two or more independent Tier A sources, this drug in the cohort, the nutrient directly measured, consistent direction, clinically meaningful magnitude, a named mechanism, no substantial contradicting Tier A evidence. RED

Limits on what this shows

  • Null/negative findings: None identified specifically contradicting the direction of this finding; the label's own "rare idiosyncrasy" language is the bounding fact on frequency, not a null result.
  • At-risk subgroups: Long-term monotherapy or polytherapy with other folate-interacting anticonvulsants; pregnancy planning (folate status is independently relevant to neural-tube-defect risk management for any anticonvulsant user, a separate clinical question from this drug-caused depletion finding).
  • Counter-evidence on record: None found this review that contradicts the depletion direction; magnitude is bounded by the labeled rarity of clinically overt megaloblastic anemia.

Regulatory status

FDA label (DailyMed SPL) lists megaloblastic anemia as "a rare idiosyncrasy to primidone and to other anticonvulsants," stating it "responds to folic acid without necessity of discontinuing medication."

Population evidence

Chanarin, Elmes & Mollin, 1958, BMJ: clinical/biochemical case study of megaloblastic anemia specifically in primidone-treated patients, with folic-acid studies confirming low folate status and reversal on folic acid. Baker et al., 1962, Experientia: biochemical study demonstrating a specific lesion in folic-acid metabolism (pteridine/thymidine-phosphorylation pathway) induced by primidone itself, not a class generalization.

Mechanism

Named: hepatic enzyme induction (shared with the phenobarbital metabolite, see PK basis) accelerating folate turnover/catabolism, with a primidone-specific biochemical lesion in folate metabolism directly demonstrated by Baker et al.

Counter-evidence held on record

This is a drug-caused deficiency finding, not a reason to self-supplement. Folic acid can interact bidirectionally with anticonvulsant metabolism; any folate repletion in a primidone patient should be directed by the prescriber or a pharmacist, not self-initiated, and is outside this document's scope to dose. No supplement dose is recommended anywhere in this dossier.

Vitamin D (bone mineral content / biochemical osteomalacia, mixed-cohort bound)

Orange — Moderate

See study details

Anticonvulsant regimens that included primidone alongside phenytoin and phenobarbital were associated with reduced bone mineral content and biochemical osteomalacia markers, but primidone's individual contribution cannot be isolated from co-administered enzyme inducers in the available controlled trials.

Full detail and limits

What the grade means here: At least one Tier A source with this drug in the cohort showing a real but bounded deficit: an exposure window, a subgroup, low frequency, or a functional rather than circulating deficit. ORANGE

Limits on what this shows

  • Null/negative findings: In the 1974 pilot study, serum calcium and magnesium were explicitly reported as not significantly different despite the real bone/seizure-threshold effect, undercutting any claim that this is a simple dietary calcium deficiency (see Fails verification).
  • At-risk subgroups: Long-term polytherapy patients, reduced sunlight exposure, institutionalized or non-ambulatory patients, classic risk markers from the anticonvulsant-osteomalacia literature of this era.
  • Counter-evidence on record: Both controlled trials studied mixed drug regimens (phenytoin + phenobarbital + primidone together in the same patients); no study in this review isolated primidone monotherapy, so the magnitude specifically attributable to primidone cannot be stated.

Regulatory status

Not flagged as a labeled warning in the label content accessible during this review (see PK basis access note); this entry rests on independent clinical-trial literature, not the label.

Population evidence

Christiansen, Rodbro & Lund, 1973, BMJ: controlled therapeutic trial in epileptic outpatients on anticonvulsant regimens including phenytoin, phenobarbital and primidone (MeSH-indexed adverse-effects terms for all three). Mean bone mineral content was 87% of normal; biochemical osteomalacia markers were present in 12-43% of patients; three months of vitamin D2 (2,000 IU/day) raised BMC by 4% versus no change on placebo. Christiansen, Rodbro & Sjo, 1974, BMJ: a controlled pilot study in the same drug-mixed population found reduced seizure frequency with added vitamin D2 versus placebo.

Mechanism

Named: hepatic enzyme induction (the same CYP450-induction pathway documented for the phenobarbital metabolite) accelerating catabolism of vitamin D to inactive polar metabolites, the long-established basis for anticonvulsant-associated osteomalacia.

Counter-evidence held on record

This reflects an accelerated-catabolism mechanism acting on vitamin D, not a dietary calcium deficiency. Vitamin D repletion in a long-term anticonvulsant patient is a decision for the prescriber or a pharmacist; no dose is recommended here.

Vitamin K (clotting-factor depression, small-series bound and partly contradicted)

Orange — Moderate

See study details

A small, primidone-containing pediatric case series found reversible depression of vitamin K-dependent clotting factors, but a larger prospective cohort of primidone-exposed pregnancies found no statistically significant excess of neonatal bleeding from enzyme-inducing antiepileptic drugs as a group.

Full detail and limits

What the grade means here: At least one Tier A source with this drug in the cohort showing a real but bounded deficit: an exposure window, a subgroup, low frequency, or a functional rather than circulating deficit. ORANGE

Limits on what this shows

  • Null/negative findings: Kaaja, Kaaja, Matila & Hiilesmaa, 2002, Neurology: prospective cohort of 662 epilepsy pregnancies (667 neonates) versus 1,324 control neonates, with exposure specifically broken out by drug including primidone (n=11). A bleeding complication occurred in 5/667 (0.7%) enzyme-inducing-AED-exposed neonates versus 2/1,324 (0.4%) controls (p=0.3); after adjustment, bleeding was associated with preterm birth and maternal alcohol use, not with enzyme-inducing AED exposure (adjusted OR 1.1, 95% CI 0.3-4.6, p=0.8).
  • At-risk subgroups: Neonates of mothers on primidone or other enzyme-inducing antiepileptic drugs in late pregnancy, the population already covered by standard prenatal vitamin K prophylaxis practice.
  • Counter-evidence on record: The Kaaja 2002 cohort is Tier A, drug-specific (primidone n=11 named), and substantially larger than the Solomon 1977 series; it found no significant clinical bleeding excess, which is why this entry is capped at orange rather than red despite real, reversible laboratory-level clotting-factor changes in the smaller series.

Regulatory status

Not addressed in the label content accessible during this review; this entry rests on independent clinical literature.

Population evidence

Solomon, Hilgartner & Kutt, 1977: 9 children on anticonvulsant therapy including phenytoin, phenobarbital, primidone, carbamazepine, diazepam and ethosuximide; 6 of 9 showed elevated prothrombin time, elevated partial thromboplastin time, and diminished factors VII, IX and X (vitamin K-dependent), which returned toward normal when hepatic drug levels were reduced. Clinical bleeding was minor (venipuncture oozing, increased bruising) in this series.

Mechanism

Named: hepatic enzyme induction affecting synthesis/turnover of vitamin K-dependent clotting factors; a transplacental version of this mechanism is the basis for standard prenatal vitamin K prophylaxis guidance in women on enzyme-inducing antiepileptic drugs.

Counter-evidence held on record

Standard prenatal and neonatal vitamin K practice already accounts for enzyme-inducing antiepileptic drug exposure. This entry does not change that standard of care and does not support self-directed vitamin K supplementation; no dose is recommended here.

No entries remain ungraded after this repair pass

Not graded — disclosed evidence gap

See study details

No entries remain ungraded after this repair pass

Full detail and limits

What the grade means here: Nothing has been measured here, so this finding cannot be graded. That does not establish either safety or harm, and it is not the same as a White result. NONE

Limits on what this shows

  • Why no grade: Not applicable. All seven mandatory physiological categories, previously disclosed as ungraded due to a session-level access restriction, were re-researched once PubMed search-listing pages and the OpenAlex single-record lookup endpoint became reachable. Each now carries at least yellow-tier, phenobarbital-metabolite-specific or primidone-specific evidence; see the graded entries above and the Overlap map below for how shared sources are disclosed.

Channels tried this pass

WebSearch: exhausted (0 of this session's budget remained before this repair pass began). PubMed search-listing pages: intermittently reachable, succeeded for several phrasings. Europe PMC webpages (europepmc.org): disallowed by robots.txt. Europe PMC REST API, Semantic Scholar Graph API, Crossref API: returned HTTP 429 on every attempt this pass. OpenAlex single-record lookup (api.openalex.org/works/pmid:): the one channel that became reliably reachable after an initial 429 and a roughly 90-second wait, and was used to retrieve bibliographic detail and, where present, abstracts for every new source below. Individual PubMed article pages (pubmed.ncbi.nlm.nih.gov/{PMID}/): consistently blocked by a reCAPTCHA wall, consistent with the prior pass.

Candidates found but not used

Several sources were opened and read but did not support a grade and are disclosed in Sources rather than silently dropped: Tutor-Crespo et al. 2003 (phenobarbital appears only as a keyword, not confirmed in the actual patient cohort); Mukhtar et al. 2022 (studies the gut microbiome absorbing phenobarbital, the reverse direction from this category's drug-affects-microbiome scope, Hard Rule 4); Montgomery et al. 1974 (concerns cytochrome P450 heme-iron electronic structure, not nutritional iron status); Becking 1972 (dietary iron affecting drug metabolism, the reverse direction, Hard Rule 4).

The five body-system areas

Each finding is counted once, in a single area. Where a study is mentioned in a second area it is context only.

Mitochondrial Burden

Each finding below is counted once, in this area only.

Mitochondrial burden (isolated-mitochondria evidence via phenobarbital metabolite, partially contradicted)

Yellow — Low

See study details

Phenobarbital, primidone's major active metabolite, directly damages isolated liver mitochondria in vitro, but a separate in vivo intact-liver study found no consistent effect on mitochondrial respiration, so this remains mechanistic and bounded rather than established in a living organism.

Full detail and limits

What the grade means here: Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction. YELLOW

Limits on what this shows

  • Null/negative findings: Ngala Kenda & Lambotte, 1981, Eur Surg Res: in intact (not isolated) rat liver, phenobarbital showed "no consistent effect" on mitochondrial respiration in normal or partially hepatectomized rats, and enzyme induction was not associated with an increase in mitochondrial phosphorylation. This null finding in a whole-organ, in vivo model is direct counter-evidence to the isolated-mitochondria findings above and is why this entry is capped at yellow.
  • At-risk subgroups: Not established for primidone or phenobarbital in living patients; all drug-specific structural evidence here is ex vivo (isolated mitochondria) or a small, attribution-uncertain pediatric pilot study.
  • Counter-evidence on record: See null in vivo finding above (Ngala Kenda & Lambotte, 1981). No commonly circulating consumer claim specific to primidone mitochondrial damage was identified; this entry is published as mechanistic evidence, not a rebuttal of a circulating claim.

Regulatory status

Not addressed in the label content accessible during this review.

Population evidence

Santos et al., 2008, Toxicology in Vitro: phenobarbital, phenytoin, and carbamazepine (named individually, each tested) applied to mitochondria isolated from rat liver. Phenobarbital exposure induced mitochondrial swelling, depolarization of the inner mitochondrial membrane, and disrupted calcium signaling, dose-dependently. Berger et al., 2010, J Child Neurol: a small pilot study measuring mitochondrial ATP production and respiratory-chain complex II-IV activity in peripheral white blood cells of children on antiepileptic drugs including phenobarbital found that "several" of the drugs tested impaired mitochondrial phosphorylation; the drug-by-drug breakdown attributing this specifically to phenobarbital could not be confirmed from the abstract metadata accessible this session, so this source is disclosed as corroborating context only, not a primary pillar of this grade.

Mechanism

Named: direct phenobarbital exposure disrupts inner mitochondrial membrane integrity and calcium handling in isolated hepatic mitochondria (Santos et al.). Marzatico et al., 1987, found phenobarbital alters rat brain cytochrome c oxidase, succinate dehydrogenase, and related energy-metabolism enzyme activities, though the specific direction and magnitude could not be confirmed from the metadata accessible this session.

Counter-evidence held on record

This is mechanistic, drug-specific evidence at the theoretical/low tier, not an established clinical finding, and is contradicted in part by a whole-organ null result. It does not support any supplement or monitoring recommendation beyond the general prescriber-directed guidance in the Monitoring panel.

Oxidative Stress

Each finding below is counted once, in this area only.

Oxidative stress (phenobarbital-specific hepatic nuclear ROS production)

Yellow — Low

See study details

Phenobarbital, dosed to rats to induce the same hepatic enzyme system implicated in primidone's classical nutrient findings, also increases NADPH- and NADH-dependent reactive oxygen intermediate production in isolated liver cell nuclei, a drug-specific but animal-only and mechanistic signal.

Full detail and limits

What the grade means here: Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction. YELLOW

Limits on what this shows

  • Null/negative findings: None identified this session specific to primidone or phenobarbital and oxidative stress; a dedicated search for null results in this category was not completed before this session's fetch channels degraded (see Sources access note).
  • At-risk subgroups: Not established in humans; this is an animal, enzyme-induction-linked mechanistic finding only.
  • Counter-evidence on record: None found. No commonly circulating consumer "oxidative stress/antioxidant depletion" claim specific to primidone was identified; this entry is mechanistic evidence, not a claim rebuttal.

Regulatory status

Not addressed in the label content accessible during this review.

Population evidence

Puntarulo & Cederbaum, 1992, Biochimica et Biophysica Acta: phenobarbital and 3-methylcholanthrene treatment compared for their effect on NADPH- and NADH-dependent production of reactive oxygen intermediates by rat liver nuclei. The study is phenobarbital-specific by design; the precise quantitative magnitude and whether phenobarbital's effect size differed from the comparator could not be confirmed from the metadata accessible this session (full text was not retrievable), so this is graded as mechanistic Tier B evidence of scope and direction (induction-linked reactive-oxygen production), not as a quantified effect size.

Mechanism

Named: hepatic cytochrome P450/mixed-function-oxidase induction, the same CYP450-induction pathway documented for the phenobarbital metabolite elsewhere in this dossier, is mechanistically linked to NADPH/NADH-dependent reactive oxygen intermediate generation in this study.

Counter-evidence held on record

Mechanistic, drug-specific, animal-only evidence. Does not support an antioxidant supplement recommendation; no dose is given here.

Copper and Iron Balance

Copper and iron are assessed separately. Nothing here is counted twice.

Copper (serum elevation via phenobarbital-metabolite pathway, mixed-cohort bound)

Orange — Moderate

See study details

Epileptic patients, in a cohort naming primidone specifically, show significantly elevated serum copper across all seizure types, an excess/retention signal corroborated by phenobarbital-specific animal data on increased intestinal copper absorption, not a depletion.

Full detail and limits

What the grade means here: At least one Tier A source with this drug in the cohort showing a real but bounded deficit: an exposure window, a subgroup, low frequency, or a functional rather than circulating deficit. ORANGE

Limits on what this shows

  • Null/negative findings: None identified specifically contradicting the elevation direction; Sanchez-Lastres et al., 2003, measured serum copper and ceruloplasmin in phenobarbital/phenytoin-treated children but highlighted only a calcium/phosphorus reduction as its key finding, which may suggest copper was not significantly altered in that cohort, though this could not be confirmed from the abstract metadata accessible this session (not used as supporting or contradicting evidence; see Sources).
  • At-risk subgroups: Long-term anticonvulsant polytherapy patients; the 1972 cohort was not isolated to primidone monotherapy, so a primidone-specific subgroup estimate cannot be given.
  • Counter-evidence on record: The 1972 study's own authors proposed three competing explanations or its finding: a nonspecific effect of seizure-related stress or muscular activity, a medication effect, or the underlying illness itself, and did not exclude the first two (confounding by indication/seizure activity, Hard Rule 6, is not excluded by this source alone). The cohort also mixed primidone with acetazolamide, so primidone's individual contribution cannot be isolated. Grade is capped at orange for these reasons despite a statistically significant human finding.

Regulatory status

Not addressed in the label content accessible during this review; this entry rests on independent clinical and animal literature.

Population evidence

Brunia & Buyze, 1972, Epilepsia: serum copper measured in 94 epileptic children and 80 adult patients (n=174), with anticonvulsant medication explicitly including primidone and acetazolamide. Serum copper was significantly higher than normal controls across every seizure-type classification (International Classification of Gastaut et al.), with no subtype spared.

Mechanism

Named: phenobarbital (primidone's major active metabolite, see PK basis) dose-dependently increased intestinal copper absorption in rats, from 45.7% at baseline to 56.7-70.0% across 20-80 mg/kg/day doses, with elevated liver and kidney copper content on treatment (Asano & Hokari, 1983, in situ rat intestinal recirculation study). Torronen & Marselos, 1978, independently confirmed phenobarbital alters hepatic copper accumulation in rats among a panel of tested compounds. Both are Tier B, phenobarbital-specific, not primidone-in-vivo.

Counter-evidence held on record

This is a reverse-direction, excess/retention signal, not a depletion. It is not a reason to increase dietary copper and is an active reason to avoid unsupervised copper supplementation in a primidone patient. No dose is recommended here; any concern should go through the prescriber or a pharmacist.

Iron (impaired utilization, supratherapeutic-dose bound)

Yellow — Low

See study details

A 28-day rat toxicology study found phenobarbital produced dose-dependent hypochromic anemia with altered iron-binding capacity and transferrin saturation consistent with impaired iron utilization, but only at the highest dose tested, well above typical clinical exposure, and this is mechanistically distinct from the folate-mediated megaloblastic anemia graded red elsewhere in this dossier.

Full detail, limits and 1 references

What the grade means here: Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction. YELLOW

Limits on what this shows

  • Null/negative findings: At the two lower doses tested (0.8 and 8 mg/kg/day, closer to though still above typical clinical range), the effect was not reported as significant, indicating a dose threshold. Sanchez-Lastres et al., 2003, measured serum iron, ferritin, and transferrin in phenobarbital/phenytoin-treated children but did not report them as significantly altered in the accessible abstract (only calcium/phosphorus reduction was highlighted); not used as supporting or contradicting evidence given this uncertainty.
  • At-risk subgroups: Not established in human primidone or phenobarbital patients at therapeutic dosing; this finding is animal-only and dose-threshold-bound.
  • Counter-evidence on record: No effect at the two lower, more clinically comparable doses in the same study; this is the primary reason this entry is capped at yellow rather than orange.

Regulatory status

Not addressed in the label content accessible during this review.

Population evidence

Kojima et al., 2009, Journal of Toxicological Sciences: F344 rats dosed with phenobarbital sodium at 0.8, 8, or 80 mg/kg/day orally for 28 days. At 80 mg/kg/day, significant increases in unsaturated iron-binding capacity and altered transferrin saturation accompanied a hypochromic anemia, which the authors proposed reflects impaired iron utilization rather than simple blood loss or marrow suppression. The 80 mg/kg/day rat dose is substantially above typical human therapeutic phenobarbital exposure (commonly on the order of 1-5 mg/kg/day in adults), a material bounding caveat.

Mechanism

Named: impaired iron utilization proposed by the study authors as the mechanism for the dose-dependent hypochromic anemia, distinct from the hepatic-induction/folate-catabolism mechanism behind the Folate entry's megaloblastic anemia.

Counter-evidence held on record

This is an animal, supratherapeutic-dose signal, not a confirmed human finding at clinical dosing. It does not support iron supplementation or monitoring beyond what a prescriber would already order for unexplained anemia. No dose is recommended here.

Gut Microbiome Risk

Each finding below is counted once, in this area only.

Gut microbiome risk (compositional/functional shift, animal cohort, uncertain clinical direction)

Yellow — Low

See study details

Phenobarbital treatment in a small canine epilepsy cohort altered fecal microbial composition and short-chain fatty acid production without changing overall microbial diversity, a real but small, animal-only signal whose clinical direction (harmful versus adaptive) is not established.

Full detail and limits

What the grade means here: Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction. YELLOW

Limits on what this shows

  • Null/negative findings: No change in overall alpha or beta diversity; increased short-chain fatty acid production is, if anything, a marker typically associated with better, not worse, gut epithelial and metabolic health, which argues against reading this finding as straightforward harm.
  • At-risk subgroups: Not established in human primidone or phenobarbital patients; this is a canine clinical cohort, not a human or rodent laboratory model.
  • Counter-evidence on record: The direction of clinical significance is genuinely mixed (decreased Clostridiales alongside increased beneficial-associated short-chain fatty acids), which is why this is graded as a context flag at yellow rather than a clear risk finding.

Regulatory status

Not addressed in the label content accessible during this review.

Population evidence

Watanangura et al., 2022, Frontiers in Veterinary Science: 12 dogs with idiopathic epilepsy, fecal samples compared before and 90 days after phenobarbital treatment. No significant change in alpha or beta diversity or dysbiosis index. Clostridiales abundance significantly decreased. Short-chain fatty acids increased overall, with propionate and butyrate rising significantly; phenobarbital-responders showed higher butyrate than non-responders. Functional analysis showed increased trehalose biosynthesis and gluconeogenesis pathway genes and decreased V-ATPase-related genes.

Mechanism

Not fully named; the study is descriptive (compositional and functional sequencing before/after treatment) rather than mechanistic. This is disclosed as a class-adjacent animal model (canine idiopathic epilepsy, phenobarbital-treated) rather than a distant extrapolation, since phenobarbital itself, not a different drug, was the treatment studied.

Counter-evidence held on record

This is an animal (canine) clinical finding of uncertain clinical direction, not a confirmed human gut-health risk. It does not support a probiotic, prebiotic, or dietary recommendation. No dose or intervention is given here.

Oxygen and ATP Output

Oxygen delivery and ATP production are assessed separately. Nothing here is counted twice.

ATP production (isolated-mitochondria evidence via phenobarbital metabolite, partially contradicted)

Yellow — Low

See study details

The same phenobarbital-exposure studies that show mitochondrial structural damage also show directly reduced ATP output in isolated liver mitochondria, but an in vivo intact-liver study found no change in mitochondrial phosphorylation, so this is graded independently of, but evidentially tied to, the Mitochondrial burden entry above.

Full detail and limits

What the grade means here: Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction. YELLOW

Limits on what this shows

  • Null/negative findings: Ngala Kenda & Lambotte, 1981: in intact rat liver, enzyme induction by phenobarbital was "not associated with an increase in mitochondrial phosphorylation," a direct null for this category in a whole-organ, in vivo model.
  • At-risk subgroups: Not established for primidone or phenobarbital in living patients at clinically relevant exposure.
  • Counter-evidence on record: See null in vivo finding above. No commonly circulating consumer "low energy/ATP" claim specific to primidone was identified; this entry is mechanistic evidence, not a claim rebuttal.

Regulatory status

Not addressed in the label content accessible during this review.

Population evidence

Santos et al., 2008, Toxicology in Vitro: phenobarbital exposure of isolated rat liver mitochondria produced reduced ATP production and altered oxygen consumption, consistent with impaired oxidative phosphorylation, dose-dependently. Berger et al., 2010, J Child Neurol: pilot study explicitly measuring mitochondrial ATP production in peripheral white blood cells of children on antiepileptic drugs including phenobarbital; "several" drugs tested impaired ATP production, but phenobarbital's individual contribution could not be confirmed from the metadata accessible this session and is disclosed as corroborating context only.

Mechanism

Named: direct phenobarbital exposure impairs oxidative phosphorylation and ATP synthesis in isolated hepatic mitochondria (Santos et al., same source and mechanism as the Mitochondrial burden entry; see Overlap map).

Counter-evidence held on record

Mechanistic, drug-specific, low-tier evidence only, contradicted in part by a whole-organ null result. No supplement, dosing, or monitoring change is supported by this entry alone.

Oxygen delivery/utilization (hemoglobin/hematocrit reduction, supratherapeutic-dose bound, mechanistically distinct from folate anemia)

Yellow — Low

See study details

The same 28-day rat toxicology study that found impaired iron utilization also found significant reductions in hemoglobin, hematocrit, and red cell count, but only at a supratherapeutic dose, and by a mechanism distinct from the folate-mediated megaloblastic anemia graded red elsewhere in this dossier.

Full detail, limits and 1 references

What the grade means here: Mechanistic plausibility only (Tier B), or class extrapolation (Tier C) with no drug-specific human status data; also used for context flags and interactions running the other direction. YELLOW

Limits on what this shows

  • Null/negative findings: Not reported as significant at the two lower doses (0.8 and 8 mg/kg/day) in the same study, indicating a dose threshold well above typical clinical exposure.
  • At-risk subgroups: Not established in human primidone or phenobarbital patients at therapeutic dosing.
  • Counter-evidence on record: No effect at the two lower, more clinically comparable doses in the same study; primary reason this entry is capped at yellow.

Regulatory status

Not addressed in the label content accessible during this review.

Population evidence

Kojima et al., 2009, Journal of Toxicological Sciences (same source as the Iron entry; see Overlap map): at 80 mg/kg/day phenobarbital sodium for 28 days, F344 rats showed significant reductions in hematocrit, hemoglobin concentration, and erythrocyte count, with changes in mean cell hemoglobin concentration in mature erythrocytes and increased reticulocytes in females.

Mechanism

Named: impaired iron utilization (see Iron entry), not folate-pathway megaloblastic change. This is explicitly a different mechanism from the Folate entry's megaloblastic anemia and is not double-counted with it (see Overlap map).

Counter-evidence held on record

This is an animal, supratherapeutic-dose finding, not a confirmed effect at human therapeutic dosing, and is not the same mechanism as the red-graded folate anemia above. It does not change the existing folate-monitoring guidance and supports no new supplement recommendation. No dose is given here.

Claims checked and not supported

These circulate online for this medication. They are listed here only so they can be answered, never as findings, and they are not graded.

A claim with no supporting evidence is not necessarily disproven. Where evidence actually argues against a claim, that is stated below.

  • "Anticonvulsants (including primidone) deplete calcium, so calcium should be supplemented."

    Where it comes from: Generic anticonvulsant-and-bone-health consumer framing that conflates reduced bone mineral content with a primary dietary calcium deficiency.

    Why it fails: The drug's own controlled-trial data (Christiansen et al., 1974) found serum calcium and magnesium were not significantly altered despite a real, measurable bone and seizure-threshold effect from vitamin D supplementation in the same mixed anticonvulsant cohort. The mechanism documented in this literature is accelerated hepatic catabolism of vitamin D (and a secondary calcium-PTH-bone axis disturbance), not a direct depletion of dietary or circulating calcium. Recommending calcium supplementation on this framing targets the wrong nutrient; see the Vitamin D entry above.

How the body handles this medication

Metabolism
Hepatic; primidone itself is pharmacologically active and is further metabolized to two additional active compounds, phenobarbital and phenylethylmalonamide (PEMA). A patient on primidone is therefore exposed to three anticonvulsant substances at once.DailyMed SPL, Primidone Tablets USP (Actavis Pharma), setid ae0fa704-818e-4423-8e3a-6cc3390cdd7d
Enzyme induction
Primidone's active metabolite phenobarbital is a long-established hepatic microsomal enzyme (CYP450) inducer; pharmacokinetic-interaction reviews of this antiepileptic drug group name phenobarbital explicitly in this role. This is the mechanistic basis for the folate, vitamin D, and vitamin K signals graded below.Perucca E. Clin Pharmacokinet. 1982;7(1):57-84. PMID 7042173
Megaloblastic anemia, labeled
Primidone's own FDA label states that megaloblastic anemia may occur as "a rare idiosyncrasy to primidone and to other anticonvulsants," and that it "responds to folic acid without necessity of discontinuing medication."DailyMed SPL, Primidone Tablets USP, Adverse Reactions
Route / elimination detail accessed
The specific renal-versus-hepatic elimination percentage and any named absorption transporter were not present in the label content retrievable during this review session (see access note in Sources); this is disclosed rather than estimated.DailyMed SPL, Primidone Tablets USP, access-limited

What the research says is worth watching

General information from the medication label and the studies above. It is not personal medical advice, and any change belongs with your prescriber.

  • Lab / folate

    Baseline and periodic folate

    Red cell or serum folate at baseline and periodically during long-term primidone therapy, especially with polytherapy, pregnancy planning, or any unexplained anemia symptoms. Any folic acid repletion should be prescriber- or pharmacist-directed given anticonvulsant drug-level interactions.

  • Lab / bone

    Vitamin D and bone markers in long-term use

    Baseline 25-OH vitamin D, with consideration of alkaline phosphatase, PTH, or bone density assessment for long-term, polytherapy, reduced-mobility, or low-sun-exposure patients, consistent with the mixed-cohort anticonvulsant-osteomalacia literature above.

  • Obstetric / vitamin K

    Standard prenatal vitamin K prophylaxis

    Standard obstetric practice already addresses prenatal/neonatal vitamin K prophylaxis for enzyme-inducing antiepileptic drug exposure; this dossier's evidence does not indicate a need to change that standard of care.

  • Lab / copper, excess-risk framing

    Avoid unsupervised copper supplementation

    The copper signal above runs in the excess/retention direction, not depletion. There is no monitoring or dosing action to add here beyond avoiding copper-containing supplements without prescriber guidance; this is a caution, not a deficiency to correct.

  • Drug-interaction timing

    Any nutrient supplement through the prescriber

    Primidone has a narrow margin between seizure control and toxicity, and converts to phenobarbital and PEMA. Any nutrient supplement a patient is considering should be discussed with the prescriber or a pharmacist before starting, due to possible bidirectional drug-level effects.

  • Pregnancy

    Teratogenicity is a separate, non-nutrient risk

    Primidone's own teratogenic risk in pregnancy is a labeled pharmacologic effect of the drug, not a nutrient-deficiency finding, and is not graded in this dossier (Hard Rule 2). Any pregnancy-related nutrient question should go through the prescribing neurologist and obstetric team together.

Overlap map, to prevent double counting

  • Vitamin D

    Shares evidence with: Fails verification: calcium claim

    Note: Both rest on the same Christiansen et al., 1973/1974 source family and the same null serum-calcium/magnesium finding. The calcium rebuttal is drawn from the Vitamin D entry's own counter-evidence, not an independent source; do not count it as separate confirmation.

  • Vitamin D

    Shares evidence with: Vitamin K

    Note: Both are attributed to the same general hepatic CYP450-induction mechanism (documented via the phenobarbital metabolite relationship and Perucca, 1982), but each rests on its own separate drug-specific population evidence (Christiansen et al. for vitamin D; Solomon et al. and Kaaja et al. for vitamin K). The shared mechanism citation should not be read as two independent confirmations of causation.

  • Folate

    Shares evidence with: Oxygen delivery/utilization

    Note: The megaloblastic anemia documented under Folate is a folate-pathway clinical outcome, counted once there. The Oxygen delivery/utilization entry rests on an entirely different, iron-utilization mechanism (Kojima et al. 2009) and a different source; the two anemia signals are deliberately kept mechanistically and evidentially separate and are not double-counted as corroborating each other.

  • Iron

    Shares evidence with: Oxygen delivery/utilization

    Note: Both entries rest on the same single source, Kojima et al. 2009, and the same 80 mg/kg/day rat dose cohort: impaired iron utilization (Iron entry) and reduced hemoglobin/hematocrit/red cell count (Oxygen delivery/utilization entry) are two measurements from one study, not two independent confirmations. Listed separately per Hard Rule 7.

  • Mitochondrial burden

    Shares evidence with: ATP production

    Note: Both entries rest on the same two primary sources, Santos et al. 2008 (isolated rat liver mitochondria exposed to phenobarbital) and Berger et al. 2010 (pediatric pilot study, attribution-uncertain), and the same contradicting null source, Ngala Kenda & Lambotte 1981 (intact rat liver, no effect). Structural/membrane findings are counted under Mitochondrial burden and ATP-synthesis findings under ATP production from the same underlying experiments; not two independent confirmations. Listed separately per Hard Rule 7.

  • Copper

    Shares evidence with: (no shared entry; two independent Tier B mechanism sources)

    Note: The Copper entry itself rests on two phenobarbital-specific animal sources (Asano & Hokari 1983; Torronen & Marselos 1978) that both found increased copper absorption/hepatic accumulation; these corroborate each other on direction but are disclosed together in that entry rather than treated as fully independent confirmations, since both are small, older rat studies using the same class of phenobarbital-induction mechanism.

All references used above
  1. DailyMed SPL, Primidone Tablets USP (Actavis Pharma) — FDA-approved labeling; metabolism to phenobarbital/PEMA, and megaloblastic anemia as a rare idiosyncrasy responsive to folic acid.
  2. Chanarin I, Elmes PC, Mollin DL. Folic-acid studies in megaloblastic anaemia due to primidone. BMJ. 1958;2(5088):80-82. — Clinical case study, primidone named in title and cohort.
  3. Baker H, Frank O, Hutner SH, Aaronson S, Ziffer H, Sobotka H. Lesions in folic acid metabolism induced by primidone. Experientia. 1962;18(5):224-226. — Biochemical mechanism study, primidone-specific.
  4. Christiansen C, Rodbro P, Lund M. Incidence of anticonvulsant osteomalacia and effect of vitamin D: controlled therapeutic trial. BMJ. 1973;4(5894):695-701. — Controlled therapeutic trial; mixed cohort of phenytoin, phenobarbital and primidone (MeSH-indexed for all three).
  5. Christiansen C, Rodbro P, Sjo O. "Anticonvulsant action" of vitamin D in epileptic patients? A controlled pilot study. BMJ. 1974;2(5916):258-260. — Controlled pilot study, same mixed anticonvulsant cohort (phenobarbital, phenytoin, primidone); serum calcium/magnesium reported unchanged.
  6. Livingston S, Pauli LL, Bowden AN. Letter: Anticonvulsants and vitamin D metabolism. Dev Med Child Neurol. 1974;16(5):683-684. — Letter format, lower evidentiary weight; primidone named alongside phenobarbital and phenytoin. Not relied on for grading; background only.
  7. Solomon GE, Hilgartner MW, Kutt H. Anticonvulsant-induced depression of clotting factors in children. J Neurol Neurosurg Psychiatry. 1977. — Small case series (n=9); cohort included phenytoin, phenobarbital, primidone, carbamazepine, diazepam, ethosuximide.
  8. Kaaja E, Kaaja R, Matila R, Hiilesmaa V. Enzyme-inducing antiepileptic drugs in pregnancy and the risk of bleeding in the neonate. Neurology. 2002;58(4):549-553. — Prospective cohort, 662 epilepsy pregnancies / 667 neonates vs. 1,324 controls; primidone broken out as n=11. No significant bleeding excess with enzyme-inducing AEDs (adjusted OR 1.1, 95% CI 0.3-4.6).
  9. Perucca E. Pharmacokinetic interactions with antiepileptic drugs. Clin Pharmacokinet. 1982;7(1):57-84. — Pharmacokinetic-interaction review naming phenobarbital as a hepatic microsomal enzyme inducer; used for mechanism, not as population evidence.
  10. Kurekci AE, Alpay F, Tanindi S, Gokcay E, Ozcan O, Akin R, Isimer A, Sayal A. Plasma trace element, plasma glutathione peroxidase, and superoxide dismutase levels in epileptic children receiving antiepileptic drug therapy. Epilepsia. 1995. — Cohort was valproate and carbamazepine only.Cohort excluded primidone and phenobarbital; not used as supporting evidence for this drug, listed for disclosure only.
  11. Jia W, Song Y, Yang L, et al. The changes of serum zinc, copper, and selenium levels in epileptic patients: a systematic review and meta-analysis. Expert Rev Clin Pharmacol. 2020. — Systematic review/meta-analysis; available metadata indicates a valproic-acid-focused analysis.Primidone/phenobarbital-specific stratification could not be confirmed from accessible metadata; not used as supporting evidence for this drug.
  12. Sarangi SC, Tripathi M, Kakkar AK, Gupta YK. Effect of antiepileptic therapy on trace elements status in Indian population in a tertiary care hospital from northern India: a cross sectional study. Epilepsy Res. 2014;108(5):917-927. — Cross-sectional study; drug list and sample size not confirmed this session.Individual article page blocked by a reCAPTCHA bot-check wall during this review; cohort composition could not be verified, so not used as supporting evidence. Flagged for re-check on a future revision.
  13. Brunia CHM, Buyze G. Serum copper levels and epilepsy. Epilepsia. 1972. — Human observational study, n=174 (94 children, 80 adults); anticonvulsant medication named included primidone and acetazolamide. Serum copper significantly elevated versus normal controls across all seizure-type classifications.
  14. Asano R, Hokari S. Effect of phenobarbital on the absorption of copper by rat small intestine. Jpn J Vet Sci. 1983;45(5):577-583. — In situ rat intestinal recirculation study; phenobarbital-specific, dose-dependent increase in copper absorption and elevated liver/kidney copper.
  15. Torronen R, Marselos M. Changes in the hepatic copper content after treatment with foreign compounds. Arch Toxicol Suppl. 1978. — Rat study; phenobarbital named among tested compounds (with disulfiram, pyrazole derivatives, and chelating agents); examined hepatic copper accumulation.
  16. Santos NA, Medina WS, Martins NM, Mingatto FE, Curti C, Santos AC. Aromatic antiepileptic drugs and mitochondrial toxicity: effects on mitochondria isolated from rat liver. Toxicol In Vitro. 2008;22(5):1143-1152. — Phenobarbital, phenytoin, and carbamazepine each tested individually on isolated rat liver mitochondria; phenobarbital induced swelling, membrane depolarization, reduced ATP production, and calcium-signaling disruption, dose-dependently.
  17. Berger I, Segal I, Shmueli D, Saada A. The effect of antiepileptic drugs on mitochondrial activity: a pilot study. J Child Neurol. 2010. — Small pediatric pilot study; phenobarbital named among drugs tested (with valproic acid, lamotrigine, carbamazepine) for mitochondrial ATP production and respiratory-chain complex II-IV activity in peripheral white blood cells.Phenobarbital was confirmed in the tested cohort, but the drug-by-drug attribution of the reported impairment could not be confirmed from the abstract metadata accessible this session; used only as corroborating context in the Mitochondrial burden and ATP production entries, not as a primary pillar.
  18. Ngala Kenda JF, Lambotte L. Oxidative phosphorylation, enzyme induction and rat liver regeneration: effect of phenobarbital. Eur Surg Res. 1981;13(2):169-177. — Intact and partially hepatectomized rats; phenobarbital-specific. Found no consistent effect on mitochondrial respiration and no increase in mitochondrial phosphorylation in vivo; used as counter-evidence/null finding for Mitochondrial burden and ATP production.
  19. Marzatico F, Dagani F, Curti D, Benzi G. Phenobarbital and 6-aminonicotinamide effect on cerebral enzymatic activities related to energy metabolism in different rat brain areas. Neurochem Res. 1987;12(1):33-39. — Phenobarbital-specific rat brain study of energy-metabolism enzymes (cytochrome c oxidase, succinate dehydrogenase, phosphofructokinase, lactate dehydrogenase, aspartate aminotransferase, NADH-cytochrome c reductase) across multiple brain regions.Specific direction and magnitude of phenobarbital's effect on each enzyme could not be confirmed from the metadata accessible this session; used as corroborating mechanistic context only in the Mitochondrial burden entry.
  20. Puntarulo S, Cederbaum AI. Effect of phenobarbital and 3-methylcholanthrene treatment on NADPH- and NADH-dependent production of reactive oxygen intermediates by rat liver nuclei. Biochim Biophys Acta. 1992;1116(1):17-23. — Phenobarbital-specific rat liver nuclei study of reactive-oxygen-intermediate production linked to hepatic enzyme induction.Precise quantitative effect size and full abstract text could not be retrieved from the metadata accessible this session (full text not reachable); graded as mechanistic Tier B evidence of scope and direction only, not a quantified effect.
  21. Kojima S, Sasaki J, Tomita M, et al. Multiple organ toxicity, including hypochromic anemia, following repeated dose oral administration of phenobarbital (PB) in rats. J Toxicol Sci. 2009;34(5):527-539. — F344 rats, 0.8/8/80 mg/kg/day phenobarbital sodium orally for 28 days. At 80 mg/kg/day: significant reductions in hematocrit, hemoglobin, and erythrocyte count, plus increased unsaturated iron-binding capacity and altered transferrin saturation consistent with impaired iron utilization as the proposed mechanism for the hypochromic anemia. No significant effect reported at the two lower doses. Used for both the Iron and Oxygen delivery/utilization entries (see Overlap map); the 80 mg/kg/day rat dose is well above typical human therapeutic exposure.
  22. Watanangura A, Meller S, Suchodolski JS, et al. The effect of phenobarbital treatment on behavioral comorbidities and on the composition and function of the fecal microbiome in dogs. Front Vet Sci. 2022. — 12 dogs with idiopathic epilepsy, fecal samples before and 90 days after phenobarbital treatment. No change in overall alpha/beta diversity; significantly decreased Clostridiales; increased short-chain fatty acids (propionate, butyrate); shifted functional gene pathways. Animal (canine) clinical cohort, phenobarbital itself the treatment studied.
  23. Tutor-Crespo MJ, Hermida J, Tutor JC. Assessment of copper status in epileptic patients treated with anticonvulsant drugs. Epilepsy Res. 2003;56(2-3):147-153. — Human study of ceruloplasmin oxidase activity as a copper-status marker in epileptic patients.Phenobarbital appears among the study's keyword metadata but could not be confirmed as present in the actual patient cohort from the information accessible this session; not used as supporting evidence for this drug.
  24. Sanchez-Lastres JM, Eiris-Punal J, Otero-Cepeda JL, Pavon-Belinchon P, Castro-Gago M. Nutritional status of mentally retarded children in northwest Spain: II. Biochemical indicators. Acta Paediatr. 2003. — 128 children; phenobarbital and phenytoin among the anticonvulsants used. Measured albumin, transferrin, ferritin, ceruloplasmin, iron, copper, calcium, phosphorus, and other markers. Only a calcium/phosphorus reduction was highlighted as a key finding.Iron, ferritin, transferrin, copper, and ceruloplasmin were measured but their specific findings for this cohort could not be confirmed from the abstract metadata accessible this session; disclosed as attempted, not used as supporting or contradicting evidence for the Iron or Copper entries.
  25. Mukhtar I, Anwar H, Iftikhar A, et al. Human targeted phenobarbital presents a poor substrate of gut microbiome deciphering new drug targets beyond pharmacokinetic curbs. BMC Pharmacol Toxicol. 2022. — In vivo rat study of phenobarbital absorption by gut microbial mass over time.Studies the gut microbiome's uptake of phenobarbital (microbiome affecting the drug), the reverse direction from the Gut microbiome risk category's scope (drug affecting microbiome), per Hard Rule 4; not used as supporting evidence for that entry.
  26. Montgomery MR, Clark C, Holtzman JL. Iron species of hepatic microsomes from control and phenobarbital-treated rats. Arch Biochem Biophys. 1974. — Rat study of phenobarbital-induced cytochrome P450/mixed-function-oxidase heme-iron electronic states in hepatic microsomes.Concerns enzyme-bound heme iron chemistry (cytochrome P450 induction), not nutritional/systemic iron status; not used as supporting evidence for the Iron entry, which rests on Kojima et al. 2009 instead.
  27. Becking GC. Influence of dietary iron levels on hepatic drug metabolism in vivo and in vitro in the rat. 1972. — Rat study of dietary iron's effect on hepatic drug-metabolizing enzymes.Studies iron affecting drug metabolism, the reverse direction from this dossier's Iron entry (drug affecting iron status), per Hard Rule 4; not used as supporting evidence.
  28. WHO Collaborating Centre for Drug Statistics Methodology. ATC/DDD Index: Primidone. — ATC code N03AA03, barbiturates and derivatives, DDD 1.25 g oral.