Intensification of a failing regimen with zidovudine may cause sustained virologic suppression in the presence of resensitising mutations including K65R

Summary Objectives The reverse transcriptase (RT)-mutation K65R limits further therapeutic options and has been selected by unfavorable RT-combinations, e.g. tenofovir in combination with abacavir and/or didanosine. Methods We identified HIV-1 infected patients from a large treatment cohort who experienced virological failure (HIV-1 RNA >1000 copies/mL) with evidence of resistance mutations including the K65R, but without thymidine analogue mutations (TAMs) in genotypic resistance assay. Phenotype was performed from previously collected frozen plasma. The patients were followed for clinical and resistance outcome after treatment intensification with only zidovudine. Results Five patients had experienced antiretroviral treatment failure on various nucleoside analogue combinations, containing abacavir, didanosine, lamivudine, nevirapine, reverset and/or tenofovir. RT-sequence revealed mutations at position K65R in combination with other non-TAMs. The patients' median viral load prior to zidovudine intensification was 3.551 Log10 (range 3.053–4.681) and despite evidence for resistance to the failing drug regimen, all responded within 4 weeks to undetectable levels ( Conclusions In virologically failing patients due to K65R- and other non-thymidine-mutations, simple regimen intensification with zidovudine resulted in sustained HIV-1 suppression. The finding of re-sensitized HIV-1 in patients may be clinically relevant.