ZONISADE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ZONISADE (ZONISADE).
Zonisamide is a sulfonamide anticonvulsant. Its precise mechanism of action is unknown, but it is believed to inhibit voltage-sensitive sodium channels and reduce T-type calcium currents, thereby stabilizing neuronal membranes and suppressing neuronal hypersynchronization. It may also modulate GABA and glutamate neurotransmission.
| Metabolism | Primarily metabolized by CYP3A4 via reductive cleavage, with secondary pathways involving acetylation and glucuronidation. Less than 30% is excreted unchanged in urine. |
| Excretion | Renal: approximately 62% (35% unchanged, 27% as glucuronide conjugate); fecal: 3%; biliary: negligible |
| Half-life | Terminal elimination half-life: 63-69 hours in adults; allows once-daily dosing; steady-state achieved in 14-21 days |
| Protein binding | 40-50% bound to plasma proteins (primarily albumin) |
| Volume of Distribution | Vd: 0.8 L/kg; indicates extensive tissue distribution including brain |
| Bioavailability | Oral: approximately 97% (almost complete absorption) |
| Onset of Action | Oral: onset of seizure protection occurs within 1-2 weeks; peak plasma concentration reached in 2-5 hours |
| Duration of Action | Duration of anticonvulsant effect: approximately 24 hours with once-daily dosing due to long half-life |
| Molecular Weight | 212.23 |
100-200 mg orally every 8 hours; maximum 600 mg/day.
| Dosage form | SUSPENSION |
| Renal impairment | CrCl 30-50 mL/min: 100 mg every 12 hours; CrCl 15-29 mL/min: 100 mg every 24 hours; CrCl <15 mL/min or hemodialysis: not recommended. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: not recommended. |
| Pediatric use | Body weight <45 kg: 1-2 mg/kg/dose every 8 hours; maximum 4 mg/kg/day. |
| Geriatric use | Start at lower end of dosing range (100 mg every 12 hours) due to age-related renal function decline; monitor renal function. |
| 1st trimester | Associated with increased risk of neural tube defects and other malformations; use only if benefit outweighs risk. |
| 2nd trimester | May cause fetal growth restriction and other adverse effects; monitor fetal growth. |
| 3rd trimester | Risk of neonatal hemorrhage and metabolic acidosis; consider alternative therapy. |
Clinical note
Comprehensive clinical and safety monograph for ZONISADE (ZONISADE).
| Placental transfer | Crosses the placenta extensively; fetal serum concentrations can reach maternal levels. |
| Breastfeeding | Excreted into breast milk; monitor infant for drowsiness, poor feeding, and potential hepatic effects. Use with caution. |
| Lactation Rating |
■ FDA Black Box Warning
Zonisamide can cause serious or fatal reactions in patients with a history of sulfonamide allergy. Cross-sensitivity may occur. Discontinue if signs of hypersensitivity develop.
| Serious Effects |
Hypersensitivity to zonisamide or sulfonamidesMetabolic acidosisSevere hepatic impairment
| Precautions | Sulfonamide hypersensitivity reactions (including Stevens-Johnson syndrome), oligohidrosis and hyperthermia (especially in children), metabolic acidosis, somnolence and fatigue, serious skin reactions, blood dyscrasias, increased seizure frequency with abrupt withdrawal, kidney stones, teratogenicity (pregnancy category D). |
| Food/Dietary | No specific food interactions. Maintain adequate hydration to reduce risk of kidney stones. Avoid alcohol as it may worsen CNS depression. |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | Zonisamide (ZONISADE) is classified as FDA Pregnancy Category C. In animal studies, it caused developmental toxicity (increased malformations, embryolethality, reduced fetal weight) at clinically relevant doses. Human data are limited; however, sulfonamide derivatives have been associated with an increased risk of congenital malformations (e.g., neural tube defects, cardiovascular anomalies) when used in the first trimester. During the second and third trimesters, exposure may lead to neonatal hemorrhage, metabolic acidosis, or withdrawal symptoms. The drug crosses the placenta. Use only if potential benefit justifies risk. |
| Fetal Monitoring | Monitor serum zonisamide levels to maintain therapeutic range (typically 10-40 mcg/mL) due to pregnancy-induced pharmacokinetic changes. Perform periodic complete blood count (CBC), liver function tests, renal function tests, and serum bicarbonate (risk of metabolic acidosis). Fetal monitoring includes ultrasound for structural anomalies (e.g., neural tube defects, cardiac malformations) in the first trimester and growth scans in the second and third trimesters. Neonates should be observed for signs of withdrawal, metabolic acidosis, and hemorrhage. |
| Fertility Effects | Zonisamide may impair male and female fertility. In animal studies, it caused decreased spermatogenesis, reduced fertility indices, and increased preimplantation loss. In humans, menstrual irregularities and anovulatory cycles have been reported. The drug may also interfere with hormonal contraception via enzyme induction, reducing contraceptive efficacy. |
| Clinical Pearls | Zonisamide is a sulfonamide anticonvulsant; check for sulfa allergy. It can cause metabolic acidosis; monitor serum bicarbonate at baseline and periodically. Contraindicated in patients with significant liver disease or creatinine clearance < 50 mL/min. Titrate slowly to reduce risk of CNS depression and nephrolithiasis. Use with caution in patients with history of kidney stones; ensure adequate hydration. |
| Patient Advice | Take the medication exactly as prescribed. Do not stop suddenly without consulting your doctor as this may increase seizure frequency. · Oral capsules can be swallowed whole or opened and sprinkled on soft food. · If you miss a dose, take it as soon as you remember unless it is close to the next dose; do not double the dose. · Avoid driving or operating heavy machinery until you know how zonisamide affects you as it may cause drowsiness, dizziness, or coordination problems. · Seek medical attention if you develop signs of a serious allergic reaction: rash, hives, difficulty breathing, swelling of the face, lips, tongue, or throat. · Contact your doctor immediately if you experience symptoms of metabolic acidosis: rapid breathing, tiredness, confusion, or irregular heartbeat. · Report symptoms of kidney stones: severe back or abdominal pain, pain during urination, or blood in urine. · Do not drink alcohol or use other central nervous system depressants as they may increase side effects. · Zonisamide may cause increased sweating and overheating leading to dehydration; avoid strenuous exercise in hot weather and maintain fluid intake. · Women of childbearing age should use effective contraception as zonisamide may reduce the efficacy of hormonal contraceptives. |