Drug Interaction Report

MONITOR: Concomitant use of CYP450 3A4 inducers with ondansetron may result in a reduced antiemetic effect, particularly after the oral administration of ondansetron. The proposed mechanism is induction of the CYP450 3A4 mediated metabolism of ondansetron. The clinical significance is unknown.

MANAGEMENT: Patients should be monitored for reduced antiemetic effects and the ondansetron dose adjusted as necessary.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of carbamazepine. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

In a small, randomized, crossover study, the administration of carbamazepine with grapefruit juice (compared to water) increased plasma drug concentrations by approximately 40%. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits.

MANAGEMENT: Patients receiving carbamazepine should be advised to avoid or limit consumption of alcohol. Given the drug's narrow therapeutic index, patients receiving carbamazepine therapy should preferably avoid the regular consumption of grapefruits and grapefruit juice to prevent any undue fluctuations in plasma drug levels. Patients should be advised to report signs of carbamazepine toxicity (nausea, visual disturbances, dizziness, or ataxia) to their physicians.