Drug Interactions between flecainide and Zoloft

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of sertraline. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills. In addition, limited clinical data suggest that consumption of grapefruit juice during treatment with sertraline may result in increased plasma concentrations of sertraline. The proposed mechanism is inhibition of CYP450 3A4-mediated metabolism by certain compounds present in grapefruit. An in-vitro study demonstrated that grapefruit juice dose-dependently inhibits the conversion of sertraline to its metabolite, desmethylsertraline. In a study with eight Japanese subjects, mean plasma levels of sertraline increased by approximately 100% and maximum plasma concentrations increased by 66% after the ingestion of three 250 mL glasses of grapefruit juice per day for 5 days and administration of a single dose of sertraline 75 mg on the sixth day. In another small study with 5 patients, mean sertraline trough levels increased by 47% after taking sertraline for at least 6 weeks, then taking sertraline with 240 mL grapefruit juice daily for 1 week. The clinical significance is unknown; however, pharmacokinetic alterations associated with interactions involving grapefruit juice are often subject to a high degree of interpatient variability. The possibility of significant interaction in some patients should be considered.

MANAGEMENT: Patients receiving sertraline should be advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how sertraline affects them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities. Some authorities recommend that consumption of grapefruit juice should be avoided during sertraline therapy.

MONITOR: Smoking cessation may lead to elevated plasma concentrations and enhanced pharmacologic effects of drugs that are substrates of CYP450 1A2 (and possibly CYP450 1A1) and/or certain drugs with a narrow therapeutic index (e.g., flecainide, pentazocine). One proposed mechanism is related to the loss of CYP450 1A2 and 1A1 induction by polycyclic aromatic hydrocarbons in tobacco smoke; when smoking cessation agents are initiated and smoking stops, the metabolism of certain drugs may decrease leading to increased plasma concentrations. The mechanism by which smoking cessation affects narrow therapeutic index drugs that are not known substrates of CYP450 1A2 or 1A1 is unknown. The clinical significance of this interaction is unknown as clinical data are lacking.

MANAGEMENT: Until more information is available, caution is advisable if smoking cessation agents are used concomitantly with drugs that are substrates of CYP450 1A2 or 1A1 and/or those with a narrow therapeutic range. Patients receiving smoking cessation agents may require periodic dose adjustments and closer clinical and laboratory monitoring of medications that are substrates of CYP450 1A2 or 1A1.