zonisamide

Action

Raises seizure threshold and reduces seizure duration, probably by stabilizing neuronal membranes through action on sodium and calcium channels

Availability

Capsules: 25 mg, 50 mg, 100 mg

Indications and dosages

➣ Adjunctive treatment of partial seizures

Adults and children older than age 16: Initially, 100 mg P.O. daily for 2 weeks, then, if required, increased to 200 mg P.O. daily for at least 2 weeks. May increase in 100-mg increments at 2-week intervals to 300 to 400 mg daily as required. Daily dosage ranges from 100 to 600 mg.

Dosage adjustment

• Hepatic or renal impairment

• Elderly patients

Off-label uses

• Infantile spasms

• Progressive myoclonic epilepsy

• Weight loss

Contraindications

• Hypersensitivity to drug or other sulfonamides

Precautions

Use cautiously in:

• hepatic or renal disease

• pregnant or breastfeeding patients

• children younger than age 16 (safety not established).

Administration

• Give with or without food.

Adverse reactions

CNS: drowsiness, fatigue, agitation, irritability, depression, dizziness, psychomotor slowing, psychosis, asthenia, abnormal gait, incoordination, tremor, ataxia, headache, confusion, impaired memory, hyperesthesia, paresthesia, seizures

EENT: diplopia, amblyopia, nystagmus, tinnitus, rhinitis, pharyngitis

GI: nausea, vomiting, diarrhea, dyspepsia, dry mouth, anorexia, pancreatitis

GU: renal calculi

Hematologic: anemia, leukopenia

Respiratory: cough

Skin: rash, pruritus, bruising, Stevens-Johnson syndrome

Other: abnormal taste, weight loss, allergic reactions, oligohidrosis and hyperthermia (in children), flulike symptoms, accidental injury

Interactions

Drug-drug. Carbamazepine, phenobarbital, phenytoin, valproic acid: decreased zonisamide blood level and effects

CYP450-3A4 inducers: decreased zonisamide half-life

CYP450-3A4 inhibitors: increased zonisamide blood level

Drug-diagnostic tests. Blood urea nitrogen, creatine kinase, creatinine: increased levels

Platelets, white blood cells: decreased counts

Patient monitoring

• Monitor CBC with white cell differential.

• Assess neurologic status; report significant adverse reactions.

• Monitor renal function tests. Watch for signs and symptoms of renal calculi.

See Monitor for rash, which may be first sign of Stevens-Johnson syndrome. If rash occurs, discontinue drug and notify prescriber immediately.

Patient teaching

• Explain therapy to patient. Instruct him to keep seizure diary and show it to prescriber.

• Instruct patient to swallow capsules whole. Advise him to drink 6 to 8 glasses of water daily to help prevent kidney stones.

See Warn patient that stopping drug abruptly may cause status epilepticus.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects him and until seizures are well controlled.

See Tell patient to immediately report rash, fever, sore throat, sudden back pain, depression, speech or language problems, or painful urination.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.