ANTIRETROVIRAL PRESCRIBING PATTERNS AFTER GENOTYPIC RESISTANCE TESTING IN THE HIV ONTARIO OBSERVATIONAL DATABASE

Ahmed M Bayoumi^1,2, Carol Major³, Tonia Forte^1,2, Peggy Millson^1,2, Gregory Robinson, Robert S Remis², Anita Rachlis^2,4
1Ontario HIV Treatment Network; ²University of Toronto; ³Ontario Public Health Laboratory; ⁴Sunnybrook and Women’s College Health Sciences Centre

Objective: To investigate antiretroviral prescribing patterns after genotypic resistance testing in a longitudinal observational cohort.
Methods: We studied individuals enrolled in the HIV Ontario Observational Database (HOOD) with complete antiretroviral medication histories and at least one genotypic resistance test. Resistance and viral load results were obtained from Ontario’s Public Health Laboratory.
Results: For 169 individuals who met our criteria, the median follow-up from the first use of antiretroviral therapy was 6.1 years (inter-quartile range ([IQR] 4.6 to 8.7 years). The median number of drugs and regimens ever used during this interval was 11 (IQR 8 to 15) and 9 (IQR 6 to 13), respectively; 151 (9.6%) regimens were initiated after genotypic test results were available. The number of successfully sequenced genotypic tests ranged from one for 145 (86%) participants to three for 2 (1%) participants. At the time of GRT, 164 individuals were using antiretrovirals. Samples from 19 of these patients (12%) had no discernible resistance to drugs in the current regimen while 89 (54%) demonstrated resistance to all drugs in the current regimen. The median number of current drugs to which resistance was demonstrated was 3 (IQR 1 to 4). We recorded changes to a new antiretroviral regimen for 73 participants after genotypic testing. For 48 (66%) participants, the new regimens contained at least one drug to which the patient’s virus was resistant. Compared to individuals who changed to fully sensitive regimens, individuals using drugs to which their virus has demonstrated resistance had similar past antiretroviral use (median 8 vs. 10 drugs, p=0.23) and were equally likely to achieve viral load drops of 1.0 log10 or greater 3 to 9 months after resistance testing (35% vs. 40%, p=0.79).
Conclusions: Prescribing antiretroviral drugs to which resistance has been documented is frequent in clinical practice, possibly due to constrained antiretroviral options.