Zonisamide

Indications
 Oral
Partial seizures
Adult: Initially, 50 mg daily in 2 divided doses, may increase to 100 mg daily after 1 wk. Thereafter, may further increase dose at wkly intervals in steps of up to 100 mg. Usual dose: 300-500 mg daily, although some patients may respond to lower doses.
Renal impairment: Dose reduction and slower titration may be needed.
Hepatic impairment: Mild to moderate: Slower titration may be needed. Severe: Not recommended.
Contraindications
 Known hypersensitivity to sulfonamide. Lactation.
Warnings / Precautions
 Pregnancy. Child. Renal or hepatic impairment. Patient at risk of nephrolithiasis; ensure adequate hydration to prevent renal stones. Discontinue use if unexplained rash develops; otherwise, frequent observation is necessary. Withdraw gradually and reduce dosage slowly. Avoid driving and operating machinery. Monitor serum creatine phosphokinase and aldolase levels if patient develops severe muscle pain or weakness; withdraw if levels are raised. Monitor pancreatic lipase and amylase levels in patients who develop pancreatitis and withdraw zonisamide if needed. Consider drug withdrawl in patients with severe weight loss. Monitor renal function periodically.
Adverse Reactions
 Abdominal pain, anorexia, diarhoea, nausea, headache, dizziness, ataxia, nystagmus, paraesthesia, confusion, difficulty in concentration, impaired memory, mental slowing, speech abnormalities, difficulty in verbal expression, agitation &/or irritability, depression, insomnia, schizophrenic behaviour, somnolence, fatigue, ecchymosis, weight loss, rash, diplopia, decreased sweating, renal stones, pancreatitis, rhabdomyolysis.
Potentially Fatal: Stevens-Johnson syndrome, toxic epidermal necrolysis, blood dyscrasias.
Overdose Reactions
 Symptoms: Bradycardia, hypotension, and respiratory depression. Management: Treatment is symptomatic and supportive. Induce emesis or perform gastric lavage to reduce drug absorption. Haemodialysis unlikely to be useful.
Drug Interactions
 Small decrease in zonisamide levels with phenytoin, phenobarbital, carbamazepine. Zonisamide has variable effects on carbamazepine levels. Increased zonisamide levels with lamotrigine.
See Below for More zonisamide Drug Interactions
Mechanism of Actions
 Zonisamide is a benzisoxazole derivative anticonvulsant containing sulfonamide. It may act on voltage sensitive sodium and calcium channels, thereby affecting neuronal firing and therefore reducing the spread of seizure discharges. It may modulate GABA mediated neuronal inhibition.
Absorption: Absorbed from GI tract; peak plasma concentration: 2-6 hr. Bioavailability: High. Food delays time to peak concentration.
Distribution: Widely distributed. Crosses placenta and distributed into breast milk. Protein binding: 40-50%; extensively bound to erythrocytes.
Metabolism: Undergoes hepatic metabolism via cytochrome P450 isoenzyme CYP3A4 to metabolites.
Excretion: Excreted mainly via urine as metabolites and unchanged drug (15-30%). Plasma elimination half life: 63 hr.
Administration
 May be taken with or without food.
Storage Conditions
 Oral: Store below 30°C.
ATC Classification
 N03AX15 - zonisamide ; Belongs to the class of other antiepileptics.
Storage
 Oral: Store below 30°C.
Available As
  • Zonisamide 100 mg
  • Zonisamide 25 mg
  • Zonisamide 50 mg

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