Adherence to protease inhibitors, HIV-1 viral load, and development of drug resistance in an indigent population

Objective: To examine the relationship between adherence, viral suppression and antiretroviral resistance in HIV-infected homeless and marginally hous ed people on protease inhibitor (PI) therapy. Design and setting: A cross-sectional analysis of subjects in an observatio nal prospective cohort systematically sampled from free meal lines, homeles s shelters and low-income, single-room occupancy (SRO) hotels. Participants: Thirty-four HIV-infected people with a median of 12 months of PI therapy. Main outcomes: Adherence measured by periodic unannounced pill counts, elec tronic medication monitoring, and self-report; HIV RNA viral load; and HIV- 1 genotypic changes associated with drug resistance. Results: Median adherence was 89, 73, and 67% by self-report, pill count, a nd electronic medication monitor, respectively. Thirty-eight per cent of th e population had over 90% adherence by pill count. Depending on the measure , adherence explained 36-65% of the variation in concurrent HIV RNA levels. The three adherence measures were closely related. Of 20 genotyped patient s who received a new reverse transcriptase inhibitor (RTI) when starting a Pi, three had primary protease gene substitutions. Of 12 genotyped patients who received a PI without a new RTI, six had primary protease gene substit utions (P < 0.03). Conclusion: A substantial proportion of homeless and marginally housed indi viduals had good adherence to PI therapy. A strong relationship was found b etween independent methods of measuring adherence and concurrent viral supp ression. PI resistance was more closely related to the failure to change RT I when starting a PI than to the level of adherence. (C) 2000 Lippincott Wi lliams & Wilkins.