Drug Interaction Report

MONITOR: Toxic serum concentrations of phenytoin and involuntary movements have been reported during coadministration with chlorpheniramine. Symptoms resolved after chlorpheniramine was discontinued. The mechanism of this interaction is not known.

MANAGEMENT: Clinical monitoring of patient response, tolerance, and serum phenytoin concentrations is recommended. Patients should be advised to notify their physician if they experience symptoms of phenytoin toxicity (drowsiness, visual disturbances, change in mental status, nausea, or ataxia) or involuntary movements.

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

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and 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 these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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.