Combinations against combinations: Associations of anti-HIV 1 reverse transcriptase drugs challenged by constellations of drug resistance mutations

The reverse transcriptase inhibitors still represent the majority of the clinically used anti-HIV drugs and constitute the main backbone of currently employed combinatorial regimens. A major obstacle to successfull chemotherapic eradication of HIV is the emergence of viral strains resistant to the drugs in use. Counteracting the emergence of resistance necessitates alternating the panel of agents employed. In order to rationally design alternative drug combinations, physicians not only must know the genotype of the emerging viral strains, but should also be able to correlate it with its resistant phenotype. However, resistant viral strains usually carry multiple mutations, whose reciprocal influences on the overall level of resistance are largely unknown. Moreover, the choice of agents to be combined must take in account drug-drug interactions and adverse metabolic effects. This review will outline the main pharmacological and clinical features of the currently utilised anti-reverse transcriptase drugs, as well as the correspondent resistance profiles selected during therapy. A major focus will be on the reciprocal influence of drug associations on their own metabolism as well as on the interacting effects of the selected combinations of drug resistance mutations.