Objective: To characterize the antiviral effect and predictors of response to ritonavir and saquinavir-based antiretroviral combination therapy.
Design: Intent-to-treat analysis with suppression of plasma viral load to levels below 2.7 log10 copies/ml as the main outcome measure.
Patients: All adult HIV-positive individuals in the province of British Columbia who started taking ritonavir and saquinavir (each at 600 mg twice daily) in combination from 1 September 1996 to 28 February 1997, with a minimum of two plasma viral load measurements, one at baseline and one after the initiation of therapy.
Results: A total of 58 participants were prescribed ritonavir and saquinavir. The median plasma viral load at entry was 4.80 log10 copies/ml (interquartile range, 4.51-5.15 log10 copies/ml). A total of 29 (50%) subjects demonstrated a decrease in plasma viral load to levels below 2.7 log10 copies/ml. This level of suppression was associated with higher baseline CD4 cell counts (P=0.022) and no prior exposure to protease inhibitors (P=0.001). After controlling for baseline CD4 cell count and plasma viral load, participants naive to protease inhibitors were almost seven times (odds ratio, 6.99; 95% confidence interval, 1.85-26.39; P=0.004) more likely to suppress their plasma viral load to below 2.7 log10 copies/ml than those who had previously used protease inhibitors.
Conclusion: Our analysis demonstrates that a ritonavir and saquinavir-based combination can produce a substantial decrease in plasma viral load with half of the participants decreasing their plasma viral load to below the limit of quantification of the assay. This response, however, is seriously compromised by prior exposure to protease inhibitors.