Increased Resilience to the Development of Drug Resistance with Modern Boosted Protease Inhibitor. Part 2
HIV/AIDS drug distribution program.The British Columbia Centre for Excellence in HIV/AIDS (BC‐CfE) distributes antiretroviral agents at no cost to all eligible HIV‐infected individuals through its drug distribution program, the HIV/AIDS Drug Treatment Program (BC‐CfE DTP). This program has been described in detail elsewhere. ART is distributed according to the specific guidelines generated by the Therapeutic Guidelines Committee. The BC‐CfE’s guidelines have been regularly updated and remain consistent with those of the International AIDS Society–USA. The BC‐CfE DTP has received ethical approval from the University of British Columbia Ethics Review Committee at its St. Paul’s Hospital site.
Study participants. Eligible study participants were 18 years old and were naive to ART when they started HAART (consisting of 2 nucleosides/nucleotides plus either a nonboosted PI, an NNRTI, or a PI plus <800 mg of ritonavir [boosted PI]). Participants started treatment between 1 August 1996 and 30 November 2004 and were followed up until 30 November 2005 ( , with median follow‐up of 4.8 years and a total of 6066 tests). Participants must have had a CD4 cell count and pVL measurement within 6 months of the first antiretroviral start date. Study data from eligible participants were extracted from the BC‐CfE’s monitoring and evaluation system to form the HOMER (HAART Observational Medical Evaluation and Research) cohort. The characteristics of this study population have been extensively described elsewhere. Data collection.HIV‐positive individuals receiving ART in British Columbia are entered into an Oracle‐based monitoring and evaluation system that uses standardized indicators to prospectively track antiretroviral use and the clinical health status of these individuals. Physicians enrolling an HIV‐infected individual into the system must complete a drug request enrollment prescription form, which compiles information on the participant’s address, past HIV‐specific drug history, CD4 cell counts, pVL, current drug requests, and the enrolling physician. A qualified practitioner reviews all requests to verify that they follow the therapeutic guidelines outlined by the BC‐CfE. Approved prescriptions are renewed every 1 to 3 months. The BC‐CfE recommends that pVLs and CD4 cell counts be monitored at baseline, at 4 weeks after the start of ART, and every 3 months thereafter. pVLs are determined using the Roche Amplicor Monitor assay (Roche Diagnostics) by either the standard method or the ultrasensitive adaptation (since 1999). CD4 cell counts are measured by flow cytometry, followed by fluorescent monoclonal antibody analysis (Beckman Coulter).
Resistance testing was performed on stored pVL samples extracted manually or automatically using guanidinium‐based buffer, followed by ethanol washes. Protease (PR) and reverse‐transcriptase (RT) genes were amplified from plasma HIV‐1 RNA by nested RT polymerase chain reaction (PCR), as described elsewhere. PCR products were sequenced in both the 5′ and 3′ directions using an ABI automated sequencer, and a consensus sequence was generated. Results of the genotyping analysis are reported here as amino acid changes in the HIV PR and RT genes with respect to a wild‐type reference sequence (HIV HXB2; GenBank accession number K03455). Samples were assigned to 1 of 4 resistance categories on the basis of a modification of the International AIDS Society–USA table. Samples were considered to be resistant if they displayed 1 or more major resistance mutations in any of the following 4 categories: lamivudine (184I/V); any other nucleoside reverse‐transcriptase inhibitors (NRTIs; 41L, 62V, 65R, 67N, 69D or insertion, 70R, 74V, 75I, 151M, 210W, 215F/Y, or 219E/Q); any NNRTIs (100I, 103N, 106A/M, 108I, 181C/I, 188C/H/L, 190A/S, P225H, M230L, or 236L); and any PIs (30N, 46I/L, 48V, 50L/V, 54V/L/M, 82A/F/S/T, 84V, or 90M). Lamivudine resistance was analyzed as a separate category because of the very common appearance of this mutation and the lack of cross‐resistance conferred to other NRTIs. The percentage of samples that were obtained while individuals were being actively prescribed any ART were as follows: 82% for first lamivudine resistance, 78% for other NRTIs, 84% for NNRTIs, and 81% for PIs. Because genotyping does not yield consistently successful results for samples with low pVL, samples with a pVL <1000 copies/mL were not systematically genotyped and were assumed to have no drug‐resistance mutations. We conducted a sensitivity analysis to assess the impact of our assumption that samples with a pVL <1000 copies/mL harbored no drug‐resistance mutations. For the sensitivity analysis, we repeated the original analysis only for those individuals with at least 1 sample that had a pVL 1000 copies/mL. Resistance data from those who started therapy between August 1996 and September 1999 have been reported elsewhere.