Drug Interaction Report

MONITOR: Phenytoin has been reported to increase the clearance of theophylline by 40% to 50%, presumably by enhancing the hepatic CYP450 metabolism of theophylline. Also, coadministration of theophylline has been reported to lower serum phenytoin concentrations. Other hydantoins and hepatically metabolized methylxanthines may also interact.

MANAGEMENT: Management consists of monitoring clinical response and serum concentrations of both drugs and adjusting dosages as necessary. Patients should be advised to report loss of seizure control or worsening of respiratory symptoms to their physician.

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.