Zonisamide Disease Interactions

The use of carbonic anhydrase inhibitors may rarely cause bone marrow suppression and blood dyscrasias at recommended dosages. Aplastic anemia, thrombocytopenia or thrombocytopenia purpura, leukopenia, agranulocytosis, and hemolytic anemia have been reported. Extreme caution should be exercised if carbonic anhydrase inhibitors are administered to patients with these preexisting conditions. A baseline CBC and platelet count is recommended, as well as monitoring at regular intervals during therapy.

Oligohidrosis (decreased sweating) and hyperthermia have been reported in association with the use of some carbonic anhydrase inhibitor anticonvulsants such as topiramate and zonisamide. Most of the reports have been in children. Caution and close monitoring of body temperature is advised when prescribing these drugs, especially in patients with a fever, in hot weather, or if combined with other drugs that predispose to heat related disorders. Zonisamide is not approved for use in pediatric patients in the U.S.

The use of carbonic anhydrase inhibitors is contraindicated in patients with marked liver disease or cirrhosis. Carbonic anhydrase inhibitors increase the risk of developing hepatic encephalopathy in these patients. Extreme caution should be exercised if carbonic anhydrase inhibitors are administered in patients with mild to moderate liver disease as the clearance of the drug can be decreased. A dose reduction might be needed and monitoring of the liver function is recommended.

The use of sulfonamides has been associated with hematologic toxicity, including methemoglobinemia, sulfhemoglobinemia, leukopenia, granulocytopenia, eosinophilia, hemolytic anemia, aplastic anemia, purpura, clotting disorder, thrombocytopenia, hypofibrinogenemia, and hypoprothrombinemia. Acute dose-related hemolytic anemia may occur during the first week of therapy due to sensitization, while chronic hemolytic anemia may occur with prolonged use. Patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency should be observed closely for signs of hemolytic anemia. Therapy with sulfonamides should be administered cautiously in patients with preexisting blood dyscrasias or bone marrow suppression. Complete blood counts should be obtained regularly, especially during prolonged therapy (>2 weeks), and patients should be instructed to immediately report any signs or symptoms suggestive of blood dyscrasia such as fever, sore throat, local infection, bleeding, pallor, dizziness, or jaundice.

The use of sulfonamides is associated with large increases in the risk of Stevens-Johnson syndrome, toxic epidermal necrolysis and other serious dermatologic reactions, although these phenomena are rare as a whole. Hepatitis, pneumonitis, and interstitial nephritis have also occurred in association with sulfonamide hypersensitivity. Therapy with sulfonamides should be administered cautiously in patients with severe allergies, bronchial asthma or AIDS, since these patients may be at increased risk for potentially severe hypersensitivity reactions. Patients should be instructed to promptly report signs and symptoms that may precede the onset of cutaneous manifestations of the Stevens-Johnson syndrome, such as high fever, severe headache, stomatitis, conjunctivitis, rhinitis, urethritis, and balanitis. Sulfonamide therapy should be stopped at once if a rash develops.

Antiepileptic drugs including zonisamide can increase depression and suicidal thoughts or behaviors in patients receiving these drugs for any indication. Patients should be monitored for the emergence or worsening of depression, suicidal thoughts and unusual changes in mood or behavior. Caregivers and family should be alert for the emergence or worsening of symptoms. Behaviors of concern should be reported immediately to the healthcare providers.

Antiepileptic drugs (AEDs) have been associated with an increased risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Pooled analyses of 199 placebo-controlled clinical studies involving the use of 11 different AEDs showed that patients receiving AEDs had approximately twice the risk of suicidal thinking or behavior compared to patients receiving placebo. AEDs should be administered cautiously in patients with depression or other psychiatric disorders; phentermine-topiramate should be avoided in patients with history of suicidal attempts or active suicidal ideation. The risk of suicidal thoughts and behavior should be carefully assessed against the risk of untreated illness, bearing in mind that epilepsy and many other conditions for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Patients, caregivers, and families should be alert to the emergence or worsening of signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts or behavior. If patients have symptoms of suicidal ideation or behavior, a dosage reduction or treatment discontinuation should be considered.

The major route of elimination of carbonic anhydrase inhibitors is through the kidney. These drugs should be administered cautiously in patients with reduced renal function and a dose adjustment might be required depending on the level of impairment.

Reduced plasma bicarbonate levels and, in some instances, elevated plasma chloride levels may result in metabolic acidosis during long-term therapy with carbonic anhydrase inhibitors. Therapy with carbonic anhydrase inhibitors should be administered cautiously in patients with metabolic or hyperchloremic acidosis or with conditions that predispose to acidosis (renal disease, severe respiratory disorders, diarrhea). The measurement of baseline and periodic serum bicarbonate is recommended. If metabolic acidosis develops (it may be corrected by administration of sodium bicarbonate), and persists, a dose reduction or treatment discontinuation should be considered.

The use of zonisamide may infrequently be associated with the development of nephrolithiasis. The reported incidence for clinically possible or confirmed kidney stones was 4.0% (40 of 991 patients) during premarketing use, representing a rate of 34 per 1000 patient-years of exposure (40 patients with 1168 years of exposure). Therapy with zonisamide should be administered cautiously with adequate hydration in patients with a history of nephrolithiasis. Patients who are dehydrated may be at increased risk for the development of nephrolithiasis and should be encouraged to consume additional amounts of liquid during zonisamide therapy.

The abrupt withdrawal of zonisamide capsules in patients with epilepsy may precipitate the increase of seizure frequency or status epilepticus. Caution is advised when using this drug in patients with seizures. Dose reduction or discontinuation should be done gradually.