No pharmacokinetic interactions occur between foscarnet and didanosine,zalcitabine or zidovudine. The UK manufacturer does not recommend concurrent use of lamivudine and foscarnet.
Clinical evidence,mechanism, importance and management
In a three-phase study,12 HIV-positive patients were given 4 doses of intravenous foscarnet 90 mg/kg, 4 doses of oral didanosine 200 mg, and 4 doses of both drugs together. Based on data obtained from these patients (drug clearance, volume of distribution, half-life, mean residence time), no pharmacokinetic interactions were said to occur between these two drugs. This suggests that no dosage adjustments will be needed during concurrent use (See reference number 1). The antiretroviral effects of foscarnet and didanosine were synergistic (See reference number 2).
Note that US manufacturer does not make any recommendation (See reference number 4)
Intravenous foscarnet 90 mg/kg every 12 hrs and oral zalcitabine 750 micrograms every 8 hrs were given to 12 HIV-positive subjects for 2 days. There were no clinically significant alterations in pharmacokinetics of either drug (See reference number 7). However, manufacturers of zalcitabine(See reference number 8,9) suggested that concurrent use of zalcitabine and foscarnet should be well monitored, because foscarnet may possibly decrease renal clearance of zalcitabine, thereby increasing its serum levels and its toxicity, particularly peripheral neuropathy. The antiretroviral effects of foscarnet and zalcitabine were synergistic (See reference number 2).
No significant alteration in pharmacokinetics of either drug was seen in a 14-day study in 5 AIDS patients given both drugs (See reference number 10). Foscarnet does not appear to affect zidovudine intracellular activation,(See reference number 11) and manufacturer notes that there was no evidence of increased myelotoxicity when foscarnet was used with zidovudine (See reference number 12)
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