Drug Interaction Report

MONITOR: Acyclovir may significantly increase the serum levels of lithium. A case of lithium toxicity was reported in a patient stabilized on lithium for several years who was treated with intravenous acyclovir 10 mg/kg for 6 days for herpes zoster. Serum lithium levels increased fourfold. Acyclovir may competitively inhibit the glomerular filtration of lithium, and this interaction may be dependent on the dose of acyclovir.

MANAGEMENT: Frequent monitoring of lithium levels and close observation for signs of lithium toxicity are recommended during acyclovir therapy. Patients should be advised to notify their physician if they experience symptoms of possible lithium toxicity such as drowsiness, dizziness, weakness, ataxia, vomiting, diarrhea, thirst, blurry vision, tinnitus, tremor, or increased urination.

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: One study has suggested that caffeine withdrawal may significantly increase blood lithium levels. The mechanism may be involve reversal of a caffeine-induced increase in renal lithium excretion.

MANAGEMENT: When caffeine is eliminated from the diet of lithium-treated patients, caution should be exercised. When caffeine consumption is decreased, close observation for evidence of lithium toxicity and worsening of the psychiatric disorder is recommended. Patients should be advised to notify their physician if they experience symptoms of possible lithium toxicity such as drowsiness, dizziness, weakness, ataxia, tremor, vomiting, diarrhea, thirst, blurry vision, tinnitus, or increased urination.