To identify viral genetic determinants associated with the virological efficacy of foscarnet salvage therapy.
Thirteen patients received foscarnet at a fixed dose of 80 mg/kg twice daily for 14 days, in combination with zidovudine or stavudine.
The baseline median HIV viral load and CD4 cell count were 5.10 log10 copies/ml and 23 cells/mm3, respectively. Following foscarnet therapy, viral load fell by a median of 1.84 log10 copies/ml (range: −0.29 to −2.82), and by at least 1 log10 copies/ml in 11 patients, all of whom harboured viruses with at least three thymidine-associated mutations (TAMs). The two patients with smaller declines in viral load (<0.50 log10 copies/ml) harboured viruses with only one or zero TAMs.
These findings corroborate, in vivo, the impact of TAMs on HIV susceptibility to foscarnet. The virological response to foscarnet salvage therapy in multiclass-experienced patients may thus differ according to the number of TAMs.