Drug Interaction Report

MONITOR: Coadministration with cycloserine or its prodrug, terizidone, may increase the serum levels of phenytoin. The precise mechanism of interaction has not been established, but may involve inhibition of phenytoin metabolism via CYP450 2C9 and/or 2C19.

MANAGEMENT: Caution is advised when phenytoin is coadministered with cycloserine or terizidone. Phenytoin serum levels and pharmacologic effects should be closely monitored and the dosage adjusted accordingly, particularly following initiation, discontinuation or change of dosage of the antituberculosis agent. Patients should be advised to contact their physician if they experience signs and symptoms of phenytoin toxicity such as nausea, vomiting, tremors, ataxia, lethargy, slurred speech, visual disturbances, and changes in mental status.

GENERALLY AVOID: Coadministration with alcohol may potentiate some of the central nervous system adverse effects of cycloserine and its prodrug, terizidone. These effects may include dizziness, drowsiness, depression, anxiety, psychoses, memory impairment, confusion, and convulsions.

MANAGEMENT: Patients should be advised to avoid the consumption of alcohol during treatment with cycloserine or terizidone. The use of these medications is contraindicated in patients with chronic alcohol consumption or alcoholism.

MONITOR CLOSELY: Coadministration with caffeine may potentiate some of the central nervous system adverse effects of cycloserine and its prodrug, terizidone. These effects may include insomnia, excitability, irritability, anxiety, tremor, psychoses, and convulsions.

MANAGEMENT: Caution is advised when cycloserine or terizidone is used with caffeine. Consumption of certain beverages or stimulants with very high caffeine levels should be avoided as a precautionary measure.