Drug Interaction Report

Administration of abacavir with other agents known to use the glucuronyl transferase or alcohol dehydrogenase metabolic pathways may increase the area under the time concentration curve for both drugs. The clinical significance is unknown.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents such as chlorzoxazone. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills. In addition, in one small study, watercress was reported to increase chlorzoxazone peak concentrations, AUC, and half-life. The proposed mechanism is inhibition of CYP450 2E1 metabolism. The clinical significance is unknown.

MANAGEMENT: Patients receiving chlorzoxazone 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 chlorzoxazone affects them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities. Watercress should be avoided if an interaction is suspected; e.g., excess sedation, nausea, or headache occurs.