Zalcitabine Antacids

Aluminium/magnesium hydroxide caused a 25% reduction in the bioavailability of zalcitabine. Antacids would not be expected to have any additional pharmacokinetic effect on buffered didanos-ine preparations. 

Drugs that may interact with zalcitabine include antacids, chloramphenicol, cisplatin, dapsone, didanosine, disulfiram, ethionamide, glutethimide, gold, hydralazine, iodoquinol, isoniazid, metronidazole, nitrofurantoin, phenytoin, ribavirin, vincristine, cimetidine, metoclopramide, amphotericin, aminoglycosides, foscarnet, antiretroviral nucleoside analogs, pentamidine, and probenecid. 

Zalcitabine NRTI1 0.75 mg tid3 Administer 1 h before or 2 h after an antacid Peripheral neuropathy oral ulcerations, pancreatitis, headache, nausea, rash, arthralgias Avoid concurrent cimetidine avoid concurrent neuropathic drugs (eg, ddl, zalcitabine, isoniazid). Do not administer with lamivudine... 

Zalcitabine (ddC) is a cytosine analog with high oral bioavailability (87%) and a serum half-life of 1-2 hours. Intracellular half-life of 2.6 hours necessitates thrice-daily dosing, which limits its usefulness (Figure 49-2). Plasma levels decrease by 25-39% when the drug is administered with food or antacids. The drug is excreted renally. Cerebrospinal fluid concentrations are approximately 20% of those in the plasma. 

Didanosine3 NRTI 150-200 mg bid, depending on weight. Enteric-coated 250-400 mg qd, depending on weight 30 minutes before or 2 hours after meals Peripheral neuropathy, pancreatitis, diarrhea, hyperuricemia Contains antacid avoid alcohol avoid concurrent neuropathic drugs (eg, didanosine, zalcitabine, isoniazid)... 

Potential drug interactions include an increased AUC of zalcitabine when administered in combination with probenecid or cimetidine and decreased bioavailability when zalcitabine is coadministered with antacids or metoclopramide. Lamivudine inhibits the phosphorylation of zalcitabine in vitro, potentially interfering with its efficacy. 

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