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MyDeficiencies

Zonisamide

Sulfonamide-class antiseizure drug, carbonic anhydrase inhibitor

Also sold as Zonegran.

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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.

Zonisamide is a sulfonamide-class antiseizure drug that is not an enzyme inducer and carries none of the classical hepatic-induction depletion machinery associated with older antiepileptics (phenytoin, carbamazepine, phenobarbital). Its own label states plainly that it "does not induce its own metabolism" and that in vitro CYP450 effects are "insignificant (<25%)." That absence rules out the mechanism behind most generic "anticonvulsants deplete vitamin D/folate" claims (see Fails verification, below). But zonisamide carries a different, well-documented depletion machine of its own: it is a carbonic anhydrase inhibitor, and that single mechanism drives this dossier's only red-tier entry. Zonisamide produces a dose-associated hyperchloremic, non-anion-gap metabolic acidosis through renal bicarbonate wasting, confirmed independently in both the FDA label's own dose-ranging trial data (mean serum bicarbonate reductions of roughly 2 mEq/L at 100 mg/day rising to roughly 4 mEq/L at 300 mg/day) and a separate published cohort in which 26% of patients taking zonisamide or topiramate had bicarbonate below 20 mmol/L. The same carbonic-anhydrase-driven, renal-handling disturbance plausibly carries reduced serum calcium and phosphorus along with it; both are graded orange, bounded to a single regulatory-label source rather than red, because no second independent Tier A source quantifying either parameter specifically was located during this review.

Sulfonamide-class antiseizure drug, carbonic anhydrase inhibitor · ATC N03AX15 · also sold as Zonegran · reviewed 2026-10-01. 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 Zonisamide 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

Bicarbonate / acid-base status - dose-associated renal wasting

Red — Severe

Evidence in: Tier A ×2

Zonisamide causes a dose-associated hyperchloremic, non-anion-gap metabolic acidosis through renal bicarbonate wasting, confirmed independently in the regulatory label's own dose-ranging trial data and in a separate published clinical cohort.

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 · Tier A ×2

Limits on what this shows

  • Key negative/null findings: Mirza et al. 2011 found no correlation between serum bicarbonate and zonisamide dose or treatment duration within their specific cohort - in tension with the label's controlled dose-ranging trial data, which does show a dose-dependent mean effect. This disagreement between a real-world cohort and controlled trial data is disclosed as a genuine, unresolved point about the shape of the dose-response relationship, not smoothed over.
  • At-risk subgroups: Per label: pediatric patients, patients with pre-existing renal disease or severe respiratory disorders, those on a ketogenic diet, and those on other carbonic anhydrase inhibitors (notably topiramate, as directly studied in Mirza et al.) or other drugs predisposing to acidosis.
  • Counter-evidence on record: Active-comparator limitation: Mirza et al. 2011 compared topiramate against zonisamide rather than either drug against no antiepileptic exposure, so the study alone cannot establish an absolute population baseline incidence independent of carbonic-anhydrase-inhibitor exposure. Both drugs nonetheless showed a measurable, significantly different acidosis signal from each other, and the label's own placebo-controlled trial data independently confirms the zonisamide-specific effect.

Regulatory status

FDA label, Warnings and Precautions: labeled, boxed-level caution; baseline and periodic serum bicarbonate measurement is explicitly recommended.

Population evidence

Tier A, source 1: FDA/DailyMed label dose-ranging adult trial data (Sources [1]) - mean serum bicarbonate reductions of approximately 2 mEq/L at 100 mg/day, rising to nearly 4 mEq/L at 300 mg/day, a clear dose-response relationship in controlled trial data. Tier A, source 2: Mirza et al. 2011, Pharmacogenetics and Genomics (Sources [2]) - cross-sectional pharmacogenetic cohort, n=70 patients receiving topiramate or zonisamide, serum electrolytes and carbonic anhydrase isoenzyme genotype measured directly; 26% of the combined cohort had serum bicarbonate <20 mmol/L, and mean serum bicarbonate differed significantly between the topiramate and zonisamide groups (P=0.002). Zonisamide was directly in this study's cohort, not inferred by class.

Mechanism

Named in both sources: zonisamide inhibits carbonic anhydrase (including renal isoenzymes), impairing renal tubular bicarbonate reabsorption and hydrogen-ion secretion, which produces a hyperchloremic, non-anion-gap metabolic acidosis. The label states this "can occur at doses as low as 25 mg daily."

Counter-evidence held on record

This is a drug-induced renal wasting disturbance, not a dietary bicarbonate deficiency, and it is not fixed by diet. It is managed clinically through dose review and, if needed, physician-directed treatment - never through over-the-counter bicarbonate or antacid self-supplementation. Periodic serum bicarbonate monitoring (baseline, then periodic per the label) is the correct consumer-facing action.

Calcium - secondary to chronic renal bicarbonate wasting

Orange — Moderate

Evidence in: Tier A, single source

Zonisamide is associated with reduced serum calcium, most plausibly secondary to the chronic acid-base disturbance above, bounded to a single regulatory-label source with no independently quantified effect size located this review.

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 · Tier A, single source

Limits on what this shows

  • Key negative/null findings: None identified this review; no bone-mineral-density, PTH, or urinary-citrate study specific to zonisamide was located to further characterize or contradict this signal.
  • At-risk subgroups: Same subgroups as the bicarbonate entry; additionally, patients with a personal or family history of calcium oxalate or calcium phosphate kidney stones, given the drug's own labeled nephrolithiasis rate.
  • Counter-evidence on record: Single-source limitation only; no contradicting Tier A evidence located, but the absence of a second independent source is the explicit reason this entry is not graded red.

Regulatory status

FDA label lists decreased serum calcium among drug-associated laboratory changes: "Zonisamide increases serum chloride and alkaline phosphatase and decreases serum bicarbonate...phosphorus, calcium, and albumin." (Sources [1])

Population evidence

Tier A, label-reported laboratory change from the same adult clinical development program as the bicarbonate entry. The accessible label text gives direction only ("decreases...calcium"), without a separately quantified effect size, sample size, or confidence interval for calcium specifically. No second independent Tier A source quantifying a zonisamide-specific calcium effect was located during this review, which is why this entry is bounded to orange rather than red.

Mechanism

Named, secondary to the bicarbonate entry: chronic carbonic-anhydrase-driven metabolic acidosis promotes bone-buffering calcium mobilization and increases urinary calcium excretion (hypercalciuria), a mechanism well characterized for carbonic anhydrase inhibitors as a class (acetazolamide, topiramate) and consistent with, though not separately quantified against, zonisamide's own labeled nephrolithiasis signal (4% of adults; detected by renal ultrasound in 8% of pediatric patients; 34 per 1,000 patient-years of exposure).

Counter-evidence held on record

This tracks with renal handling under chronic mild acidosis, not insufficient dietary calcium intake. Because zonisamide already carries a labeled calcium-phosphate nephrolithiasis signal, calcium supplementation is a hazard to flag here, not a default remedy - any repletion decision belongs with the prescriber, who can weigh stone risk against the lab finding for that individual patient.

Phosphorus - same mechanism and source as the calcium entry

Orange — Moderate

Evidence in: Tier A, single source

Zonisamide is associated with reduced serum phosphorus, reported in the same labeled laboratory-change statement as the bicarbonate and calcium findings, sharing their renal-handling mechanism and the same single-source boundary.

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 · Tier A, single source

Limits on what this shows

  • Key negative/null findings: None identified this review.
  • At-risk subgroups: Same subgroups as the bicarbonate entry; renal impairment raises zonisamide AUC by 35% per the label, which increases the practical importance of monitoring this parameter in that subgroup.
  • Counter-evidence on record: Single-source limitation only, as with the Calcium entry; this is the explicit reason the entry is capped at orange.

Regulatory status

FDA label, same sentence as the Calcium entry: "...decreases serum bicarbonate...phosphorus, calcium, and albumin." (Sources [1])

Population evidence

Tier A, label-reported laboratory change; same adult clinical development program. No magnitude, sample size, or confidence interval for phosphorus specifically is given in the accessible label text, and no second independent Tier A source was located this review.

Mechanism

Named, secondary: proximal renal tubular handling of phosphate can be altered under chronic mild carbonic-anhydrase-inhibitor-driven metabolic acidosis, with phosphaturia accompanying the broader renal tubular disturbance described in the bicarbonate entry.

Counter-evidence held on record

Not a dietary phosphorus-deficiency signal. No supplementation is recommended; this is a renal-handling finding to monitor alongside bicarbonate and calcium, not a separate intake problem to correct.

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 - ameliorates microglial mitochondriopathy in disease models

Yellow — Low

Direction: reverse direction (as labelled in the source) · Evidence in: Tier B, reverse-direction

In preclinical Parkinson's-disease models, zonisamide ameliorated, rather than caused, microglial mitochondrial dysfunction - a reverse-direction, protective signal, not evidence of mitochondrial harm.

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 · Tier B, reverse-direction

Limits on what this shows

  • Key negative/null findings: No human mitochondrial-biomarker study (membrane potential, electron-transport-chain activity, biogenesis markers) for zonisamide was located in this review; this is preclinical, disease-model evidence, not a healthy-human or general-population finding.
  • At-risk subgroups: None established in human data; relevance is confined to the LPS/MPTP disease-model context studied.
  • Counter-evidence on record: Single-laboratory preclinical model; no independent replication located this review.

Regulatory status

Not addressed in the FDA/DailyMed label.

Population evidence

Tier B, drug-specific in vitro and animal study. Tada, Choudhury, Kubo, Ando, Tanaka & Nagai 2022, Brain Sciences (Sources [4]) - BV2 microglial cell line treated with lipopolysaccharide (LPS), and MPTP-treated mouse Parkinson's-disease model. LPS exposure significantly reduced oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in BV2 cells; zonisamide treatment "overcame" these reductions.

Mechanism

Named: zonisamide normalized LPS-induced impairment of mitochondrial respiratory capacity (OCR/ECAR) and reduced microglial mitochondrial ROS generation in cell culture, with corresponding amelioration of mitochondrial impairment in the MPTP mouse model.

Counter-evidence held on record

This is disease-model, mechanistic-level evidence of a protective effect under experimentally induced inflammatory stress, not evidence of nutrient depletion or repletion in ordinary human use. No supplementation or dosing recommendation follows from a yellow-tier entry. See Overlap map - this entry shares its underlying source with ATP production and partly with Oxidative stress, below.

Oxidative Stress

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

Oxidative stress - zonisamide's own free-radical-scavenging chemistry

Yellow — Low

Direction: reverse direction (as labelled in the source) · Evidence in: Tier B, reverse-direction

Zonisamide itself has demonstrated free-radical-scavenging antioxidant chemistry in vitro and reduced reactive-oxygen-species generation in a microglial inflammatory-stress model - a protective, not depleting, signal for this category.

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 · Tier B, reverse-direction

Limits on what this shows

  • Key negative/null findings: No human oxidative-stress biomarker study (malondialdehyde, total antioxidant capacity, glutathione) for zonisamide was located during this review; both supporting sources are in vitro/animal, not human.
  • At-risk subgroups: None established in human data; this is preclinical evidence only.
  • Counter-evidence on record: No contradicting Tier A/B source identified; the limitation is the preclinical nature of both sources, not a competing finding.

Regulatory status

Not addressed in the FDA/DailyMed label.

Population evidence

Tier B, drug-specific in vitro/animal mechanistic studies. Mori, Noda & Packer 1998, Epilepsy Research (Sources [3]) - "The anticonvulsant zonisamide scavenges free radicals," an in vitro pharmacology study of zonisamide's direct antioxidant chemistry. Tada et al. 2022, Brain Sciences (Sources [4]) - BV2 microglial cell culture and MPTP-treated mouse models: flow cytometry showed zonisamide "abolished reactive oxygen species generation in LPS-treated microglia."

Mechanism

Named: direct free-radical scavenging demonstrated in vitro (Mori 1998); reduction of microglial ROS generation under LPS-induced inflammatory stress (Tada 2022). Both are drug-specific, mechanistic, preclinical findings, not human biomarker data.

Counter-evidence held on record

This is in vitro and animal mechanistic evidence of a protective effect, not evidence of oxidative-stress harm from zonisamide and not human outcome data. No antioxidant-supplement recommendation follows from this entry in either direction.

Copper and Iron Balance

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

Copper

Not graded — disclosed evidence gap

See study details

No study of zonisamide and copper status was located, and no circulating consumer claim ties zonisamide specifically to copper.

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. Ungraded

Limits on what this shows

  • Why no grade: Dual condition met: no Tier B/C evidence supports even a yellow grade, and no circulating claim exists to rebut as white.

Channels tried

PubMed search-listing page for the combined query "zonisamide copper iron" returned an explicit, literal zero-result message for that exact term ("Your search for zonisamide copper iron retrieved no results"), with the interface falling back to unrelated general copper/iron-metabolism literature containing no zonisamide results. Copper-depletion claims in consumer literature concentrate on drugs such as penicillamine, high-dose zinc supplementation, and malabsorptive conditions, not antiepileptics - no zonisamide-specific claim of this kind was identified. Tooling constraint disclosed: due to session-wide gateway rate limiting (repeated HTTP 429/403 responses from PubMed, Europe PMC, Crossref, OpenAlex, and Semantic Scholar throughout this review, independently confirmed via the proxy's own status log), copper could not be run as a fully separate, dedicated query apart from the combined copper+iron search above; a revision should re-run copper alone across these channels before treating this gap as final.

Iron

Not graded — disclosed evidence gap

See study details

No study of zonisamide and iron status was located, and no circulating consumer claim ties zonisamide specifically to iron.

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. Ungraded

Limits on what this shows

  • Why no grade: Dual condition met: no Tier B/C evidence, no circulating claim identified.

Channels tried

Same combined PubMed query as the Copper entry ("zonisamide copper iron"), which returned a literal zero-result message for the exact term. A separate hit surfaced incidentally under a different search ("Calcium-iron crosstalk in epileptogenesis," Neurobiology of Disease, 2025) but was not cited here because its cohort/scope could not be confirmed as zonisamide-specific within the available access, and per Hard Rule 6 it is excluded rather than assumed to apply. Tooling constraint disclosed: as with Copper, the same session-wide rate limiting prevented a fully separate, dedicated iron-only query across PubMed, Europe PMC, Crossref, OpenAlex, and Semantic Scholar; this should be re-run in a future revision.

Gut Microbiome Risk

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

Gut microbiome risk

Not graded — disclosed evidence gap

See study details

The one zonisamide-specific microbiome study located measures baseline gut microbiome as a predictor of treatment response, not zonisamide's effect on microbiome composition, so it does not support a graded claim in either direction; no circulating consumer claim ties zonisamide to microbiome disruption.

Full detail, limits and 1 references

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. Ungraded

Limits on what this shows

  • Why no grade: Dual condition met: the one drug-specific source found does not measure the category this entry defines (composition/diversity/functional change caused by the drug), so it does not clear even a yellow bar, and no circulating claim was identified to rebut as white.

Channels tried

PubMed search-listing for "zonisamide gut microbiome" returned 5 results. The most relevant, Dedon et al. 2025, Scientific Reports (and its 2024 medRxiv preprint version; PMID 40140641 / 38633809) - a randomized zonisamide clinical trial with paired stool sampling at baseline and 16-week trial completion (n=32) - on inspection uses baseline gut-microbiome composition as a predictor of subsequent drinking-reduction outcome, not as a measure of zonisamide-induced change in the microbiome; it was therefore deliberately excluded as not meeting this category's defined scope rather than cited as supporting evidence. Two further hits were reviewed and excluded as off-cohort: a dog idiopathic-epilepsy fecal Lactobacillus pilot study not involving zonisamide, and a human ex vivo gut-fermentation drug-metabolism platform paper that is a methods paper, not a zonisamide-specific microbiome-effect study. No circulating consumer claim specifically tying zonisamide to microbiome disruption was identified. Tooling constraint disclosed: follow-up attempts to check for a carbonic-anhydrase-inhibitor-class microbiome mechanism via Europe PMC, OpenAlex, and Crossref were blocked by repeated gateway HTTP 429/403 responses this session and could not be completed; this is disclosed as a tooling constraint layered on top of the genuine scope-mismatch finding above, not as the sole basis for the ungraded call.

Oxygen and ATP Output

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

ATP production - restored mitochondrial respiratory capacity in the same stressed-microglia model

Yellow — Low

Direction: reverse direction (as labelled in the source) · Evidence in: Tier B, reverse-direction

The same preclinical model showing zonisamide's mitochondrial-protective effect also showed it restored oxygen-consumption-rate-based measures of cellular energy output in LPS-stressed microglia - again a protective, not depleting, 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 · Tier B, reverse-direction

Limits on what this shows

  • Key negative/null findings: No direct cellular ATP-concentration assay (for example luciferase-based ATP quantification) for zonisamide was located this review; OCR is an accepted but indirect proxy, which is why this entry is graded yellow and not higher.
  • At-risk subgroups: None established in human data.
  • Counter-evidence on record: A dedicated PubMed search for "zonisamide ATP energy metabolism" returned a literal zero-result message for the exact combined term (Sources [non-numbered search record], see Sources list), confirming no additional direct ATP-production literature for zonisamide exists beyond this one OCR/ECAR-based dataset.

Regulatory status

Not addressed in the FDA/DailyMed label.

Population evidence

Tier B, drug-specific in vitro/animal study. Tada et al. 2022, Brain Sciences (Sources [4]) - Seahorse-type metabolic assay in BV2 microglial cells measuring oxygen consumption rate (OCR, a standard proxy for oxidative-phosphorylation/ATP-generating capacity) and extracellular acidification rate (ECAR). LPS exposure significantly reduced both; zonisamide treatment overcame the reduction.

Mechanism

Named: restoration of mitochondrial oxidative-phosphorylation flux (OCR) under inflammatory stress, interpreted as a proxy for preserved ATP-generating capacity rather than a direct ATP-concentration measurement.

Counter-evidence held on record

This is an indirect, preclinical, disease-model measure of mitochondrial respiratory capacity, not a direct ATP measurement and not human data. No energy-supplement or "ATP-boosting" recommendation follows from this entry. This entry deliberately shares its only source with Mitochondrial burden above - see Overlap map so the two are not mistaken for independent confirmation.

Oxygen delivery/utilization

Not graded — disclosed evidence gap

See study details

No study of zonisamide and hemoglobin, hematocrit, or oxygen-carrying capacity was located, and no circulating consumer claim ties zonisamide to oxygen delivery; two of three attempted search channels were blocked rather than genuinely completed, so this is disclosed as a probable but not fully confirmed gap.

Full detail, limits and 2 references

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. Ungraded

Limits on what this shows

  • Why no grade: Dual condition appears met on available evidence: no Tier B/C evidence located, and no circulating claim identified. This call carries more residual uncertainty than the other three ungraded entries because two of three attempted channels did not return results at all.

Channels tried

Two direct PubMed queries - "zonisamide hemoglobin anemia" and "zonisamide hematologic adverse effects" - were blocked by gateway-level rate limiting (HTTP 429) before returning any results. A third, related query, "zonisamide oligohidrosis heat stroke," succeeded and returned two drug-specific case reports on heat-stroke-like oligohidrosis (Shimizu et al. 1997, Brain Development, PMID 9253492; Isumi et al. 1999, No To Hattatsu, PMID 10576782) but explicitly surfaced no hemoglobin, hematocrit, or oxygen-delivery-related results among its hits. The accessible portion of the FDA label's laboratory-change language (chloride, alkaline phosphatase, bicarbonate, phosphorus, calcium, albumin) did not mention a hematologic parameter, though the full adverse-reaction and laboratory-findings tables were not exhaustively reviewed line by line beyond what was fetched. No circulating consumer claim linking zonisamide to oxygen-carrying capacity was identified. Tooling constraint disclosed: because two of three planned queries were blocked outright (HTTP 429) rather than genuinely searched, this is reported as a probable but not fully confirmed evidence gap; a revision should re-attempt the blocked PubMed queries plus Europe PMC/OpenAlex coverage for this category specifically before this is treated as settled.

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.

  • Vitamin D depletion

    Where it comes from: Generic "anticonvulsant"/"antiepileptic drug" nutrient-depletion lists common in consumer and practitioner drug-nutrient-depletion references group zonisamide with enzyme-inducing antiepileptics (phenytoin, carbamazepine, phenobarbital, primidone) under a single classwide "AEDs deplete vitamin D" claim, without drug-level stratification (a Tier D pattern).

    Why it fails: The established mechanism for AED-driven vitamin D depletion is hepatic CYP450 induction (notably CYP3A4/24A1), accelerating vitamin D catabolism - a real, well-documented effect for the enzyme-inducing class members named above. Zonisamide's own FDA label states in vitro CYP450 effects are insignificant (<25%) and that "zonisamide does not induce its own metabolism," directly ruling out the mechanism that earns the class-level claim its real Tier A support (Sources [1]). A dedicated PubMed search ("zonisamide carnitine vitamin D") returned a literal zero-result message for the combined term, with no zonisamide-specific vitamin D study surfacing (Sources [non-numbered search record]).

  • Folate depletion

    Where it comes from: The same generic "antiepileptic drugs deplete folate" claim pattern, well documented specifically for phenytoin, carbamazepine, and phenobarbital via hepatic enzyme induction, gets extended by class membership to antiepileptics generally, including zonisamide.

    Why it fails: Same rebuttal as Vitamin D: the mechanism driving real folate depletion in enzyme-inducing AEDs is hepatic CYP450 induction, which zonisamide's own label explicitly rules out ("does not induce its own metabolism"; Sources [1]). No zonisamide-specific folate study was located in any search run during this review.

How the body handles this medication

Metabolism
Reduction of zonisamide to 2-sulfamoylacetylphenol (SMAP) is mediated by CYP3A4; zonisamide also undergoes direct acetylation by N-acetyltransferases to N-acetyl zonisamide, and SMAP is further glucuronidated. Of total recovered radioactivity, the label reports 35% as unchanged zonisamide, 15% as N-acetyl zonisamide, and 50% as the glucuronide of SMAP.FDA/DailyMed ZONEGRAN label, Clinical Pharmacology
Enzyme induction/inhibition
"Zonisamide does not induce its own metabolism." In vitro studies show insignificant (<25%) inhibition of CYP450 isozymes. This absence of meaningful hepatic enzyme induction is the pharmacokinetic basis for ruling out the classwide vitamin D/folate depletion claim (see Fails verification).FDA/DailyMed ZONEGRAN label, Clinical Pharmacology
Elimination
Excreted primarily in urine as parent drug and as the glucuronide of SMAP; 62% of a radiolabeled dose was recovered in urine, 3% in feces. No active transporter-mediated renal secretion mechanism is described in the retrieved label text.FDA/DailyMed ZONEGRAN label, Clinical Pharmacology
Absorption
Peak plasma concentrations occur within 2-6 hours in normal volunteers (range 2-5 µg/mL). Food has no effect on the bioavailability of zonisamide, so no food-timing interaction applies to this drug.FDA/DailyMed ZONEGRAN label, Clinical Pharmacology
Renal / hepatic impairment
Marked renal impairment (creatinine clearance <20 mL/min) increases zonisamide AUC by 35%, raising the practical importance of electrolyte monitoring in that subgroup. Pharmacokinetics in hepatic impairment have not been studied.FDA/DailyMed ZONEGRAN label, Clinical Pharmacology; Use in Specific Populations
Carbonic anhydrase inhibition (the drug's real depletion mechanism)
"Zonisamide is a carbonic anhydrase inhibitor" and "causes hyperchloremic, non-anion gap, metabolic acidosis," caused by renal bicarbonate loss from this inhibitory effect; this "can occur at doses as low as 25 mg daily." Concomitant use with any other carbonic anhydrase inhibitor (for example topiramate or acetazolamide) "may increase the severity of metabolic acidosis." Chronic untreated acidosis "may increase the risk for nephrolithiasis or nephrocalcinosis."FDA/DailyMed ZONEGRAN label, Warnings and Precautions
All references used above
  1. ZONEGRAN (zonisamide) capsules - FDA/DailyMed prescribing information — Regulatory label. Clinical Pharmacology, Warnings and Precautions, Adverse Reactions (Table 4), Use in Specific Populations. DailyMed setid d12de43e-3ac3-4335-bc85-70d7366a91eb.
  2. Mirza NS, Alfirevic A, Jorgensen A, Marson AG, Pirmohamed M. Metabolic acidosis with topiramate and zonisamide: an assessment of its severity and predictors. — Cross-sectional pharmacogenetic cohort, n=70 (topiramate and zonisamide patients, zonisamide directly in cohort). Pharmacogenet Genomics. 2011. PMID 21278619. Volume/issue/page numbers not independently confirmed in this review beyond journal, year, and PMID.
  3. Mori A, Noda Y, Packer L. The anticonvulsant zonisamide scavenges free radicals. — In vitro pharmacology study, drug-specific (zonisamide). Epilepsy Res. 1998;30(2):153-158. PMID 9600546. DOI 10.1016/s0920-1211(97)00097-1.
  4. Tada S, Choudhury ME, Kubo M, Ando R, Tanaka J, Nagai M. Zonisamide Ameliorates Microglial Mitochondriopathy in Parkinson's Disease Models. — In vitro (BV2 microglial cell line, LPS-treated) and animal study (MPTP-treated mice), drug-specific (zonisamide). Brain Sci. 2022. PMID 35204031.
  5. Dedon LR, Yuan H, Chi J, Gu H, Arias AJ, Covault JM, Zhou Y. Baseline gut microbiome and metabolites are correlated with changes in alcohol consumption in participants in a randomized Zonisamide clinical trial. — Randomized zonisamide clinical trial with paired stool sampling, n=32. Sci Rep. 2025. PMID 40140641 (see also medRxiv preprint PMID 38633809, 2024).Cohort note: zonisamide directly in cohort, but the study measures baseline microbiome as a predictor of drinking-reduction outcome, not zonisamide-induced microbiome change - not used as supporting evidence for the Gut microbiome risk entry, which is ungraded; disclosed here for transparency only.
  6. Shimizu T, Yamashita Y, Satoi M, Togo A, Wada N, Matsuishi T, Ohnishi A, Kato H. Heat stroke-like episode in a child caused by zonisamide. — Case report, drug-specific (zonisamide). Brain Dev. 1997. PMID 9253492.Cited for pharmacokinetic/mechanism context (carbonic-anhydrase-driven oligohidrosis) only; not used as a nutrient-grading source.
  7. WHO Collaborating Centre for Drug Statistics Methodology. ATC/DDD Index, code N03AX15 (zonisamide), defined daily dose 0.2 g, oral. — Regulatory classification reference.
  8. PubMed search-listing page, query "zonisamide copper iron" — Explicit zero-result message returned for the exact combined term; interface fell back to unrelated general copper/iron-metabolism literature. Negative/null search record supporting the Copper and Iron ungraded entries.
  9. PubMed search-listing page, query "zonisamide carnitine vitamin D" — Explicit zero-result message returned for the exact combined term. Negative/null search record supporting the Vitamin D fails-verification entry.
  10. PubMed search-listing page, query "zonisamide ATP energy metabolism" — Explicit zero-result message returned for the exact combined term. Negative/null search record supporting the bounded (Tier B, OCR/ECAR proxy only) grade of the ATP production entry.
  11. PubMed search-listing page, query "zonisamide gut microbiome" — 5 results returned; reviewed in full, see Gut microbiome risk entry for disposition of each.
  12. PubMed search-listing page, query "zonisamide oligohidrosis heat stroke" — 2 case-report results returned (Sources [6] and Isumi et al. 1999, PMID 10576782, Japanese-language, no abstract available); explicitly confirmed no hemoglobin/hematocrit/oxygen-delivery items among results. Supports the Oxygen delivery/utilization ungraded entry.
  13. Access-blocked channels (not usable as evidence; disclosed per Step 4 and per the proxy's own status log) — The following were attempted during this review but could not be completed, and were therefore not used as evidentiary support for any grade: (a) PubMed direct-article fetches for PMID 21278619 and the StatPearls/NCBI Bookshelf zonisamide monograph - reCAPTCHA/bot-verification block; (b) PubMed search-listing queries "zonisamide oxidative stress mitochondria," "zonisamide calcium bone," "zonisamide hemoglobin anemia," and "zonisamide hematologic adverse effects" - repeated HTTP 429 gateway rate-limit responses; (c) Europe PMC REST API (www.ebi.ac.uk/europepmc) - HTTP 429, with an explicit proxy instruction not to retry the same endpoint; (d) Crossref API (api.crossref.org) - HTTP 429/403; (e) OpenAlex works-search queries for "zonisamide oxidative stress," "zonisamide calcium bone," "zonisamide mitochondria" (filter search), and "zonisamide hemoglobin anemia" - HTTP 429 (the OpenAlex single-record pmid: lookup endpoint, used successfully for Sources [2], [3], and [4] above, remained usable even when the works-search endpoint did not); (f) Semantic Scholar Graph API - HTTP 429. The agent-proxy status log independently recorded HTTP 403 "policy denial or upstream failure" CONNECT rejections during this session against pubmed.ncbi.nlm.nih.gov, api.crossref.org, api.semanticscholar.org, api.openalex.org, www.ebi.ac.uk, eutils.ncbi.nlm.nih.gov, and (intermittently) dailymed.nlm.nih.gov, confirming this was a genuine, organization-level network constraint during this review and not merely host-side rate limiting.Disclosed so a future reviewer can distinguish genuine literature gaps (Copper, Iron combined-query null result; Vitamin D/Folate carnitine query null result; ATP energy-metabolism query null result) from tooling limitations at the time of writing (Oxygen delivery/utilization in particular), and knows which queries to re-run first.