Drug Interaction Report

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of telithromycin, which is primarily metabolized by the isoenzyme. When telithromycin was given with the potent CYP450 3A4 inducer rifampin in repeated doses, telithromycin peak plasma concentration (Cmax) and systemic exposure (AUC) decreased on average by 79% and 86%, respectively. No data are available for use with other, less potent inducers. Subtherapeutic levels of telithromycin and loss of effect may occur. Enzyme activities usually return to normal 14 days after discontinuation of the inducing agent.

MANAGEMENT: The potential for diminished therapeutic effects of telithromycin should be considered when prescribed with CYP450 3A4 inducers. Pharmacologic response to telithromycin should be monitored closely during coadministration, and alternative treatment given if an interaction is suspected. Whenever possible, telithromycin should preferably not be used during or within 2 weeks after discontinuation of treatment with a CYP450 3A4 inducer.

MONITOR: Coadministration of two or more sympathomimetic agents may increase the risk of adverse effects such as nervousness, irritability, and increased heart rate. Central nervous system (CNS) stimulants, particularly amphetamines, can potentiate the adrenergic response to vasopressors and other sympathomimetic agents. Additive increases in blood pressure and heart rate may occur due to enhanced peripheral sympathetic activity.

MANAGEMENT: Caution is advised if two or more sympathomimetic agents are coadministered. Pulse and blood pressure should be closely monitored.