Drug Interaction Report

GENERALLY AVOID: Zalcitabine can cause peripheral neuropathy in up to one-third of patients with advanced HIV disease, and concurrent use of other agents that are also associated with this adverse effect can potentiate the risk and/or severity of nerve damage. Zalcitabine-related peripheral neuropathy is a sensorimotor neuropathy characterized initially by numbness and burning dysesthesia involving the distal extremities. These symptoms may be followed by sharp shooting pains or severe continuous burning pain if the drug is not withdrawn, and progress to severe pain requiring narcotic analgesics. The neuropathy is potentially irreversible. However, with prompt discontinuation of zalcitabine, it is usually slowly reversible, although symptoms may initially progress following discontinuation.

MANAGEMENT: Use of zalcitabine with other drugs that have the potential to cause peripheral neuropathy should be avoided whenever possible. Otherwise, careful monitoring is recommended for symptoms of neuropathy such as burning, tingling, pain, numbness, or weakness in the extremities, particularly in patients with a low CD4 cell count or diabetes. Since the development of peripheral neuropathy appears to be dose-related, the recommended dosage of zalcitabine should not be exceeded. Patients should be advised to promptly discontinue zalcitabine therapy and contact their physician if neuropathy develops. Therapy may be reinstituted following resolution of neuropathy symptoms, but dosage should be reduced to one-half the initially recommended dosage. Zalcitabine should be permanently discontinued in patients who develop severe peripheral neuropathy during treatment.

GENERALLY AVOID: Use of alcohol or products containing alcohol during nitroimidazole therapy may result in a disulfiram-like reaction in some patients. There have been a few case reports involving metronidazole, although data overall are not convincing. The presumed mechanism is inhibition of aldehyde dehydrogenase (ALDH) by metronidazole in a manner similar to disulfiram. Following ingestion of alcohol, inhibition of ALDH results in increased concentrations of acetaldehyde, the accumulation of which can produce an unpleasant physiologic response referred to as the 'disulfiram reaction'. Symptoms include flushing, throbbing in head and neck, throbbing headache, respiratory difficulty, nausea, vomiting, sweating, thirst, chest pain, palpitation, dyspnea, hyperventilation, tachycardia, hypotension, syncope, weakness, vertigo, blurred vision, and confusion. Severe reactions may result in respiratory depression, cardiovascular collapse, arrhythmia, myocardial infarction, acute congestive heart failure, unconsciousness, convulsions, and death. However, some investigators have questioned the disulfiram-like properties of metronidazole. One study found neither elevations in blood acetaldehyde nor objective or subjective signs of a disulfiram-like reaction to ethanol in six subjects treated with metronidazole (200 mg three times a day for 5 days) compared to six subjects who received placebo.

MANAGEMENT: Because clear evidence is lacking concerning the safety of ethanol use during nitroimidazole therapy, patients should be apprised of the potential for interaction and instructed to avoid alcoholic beverages and products containing alcohol or propylene glycol while using oral, intravenous, or vaginal preparations of a nitroimidazole. Alcoholic beverages should not be consumed for up to 3 days after completion of systemic nitroimidazole therapy.

Zalcitabine bioavailability may be decreased by 14% if taken with meals. The mechanism and clinical significance are unknown.