Objective: Although regimens containing two protease inhibitor (PI) together with ritonavir boosting are used with the aim of improving virologic response to salvage therapy, there is little evidence to support or reject this approach. We compared the probability of attaining an undetectable HIV RNA level after using either boosted double or boosted single PI regimens.
Design: Retrospective clinical cohort.
Methods: PI-experienced subjects in a Northern California-based database who initiated either a boosted single or boosted double PI salvage therapy regimen were analysed. Traditional multivariable regression and marginal structural model analyses were used to compare the effects of the two regimens on virologic suppression 12–36 weeks after initiation of salvage therapy, controlling for confounding by baseline HIV RNA level, CD4 lymphocyte count, treatment history, drug resistance, and multiple characteristics of the salvage regimen.
Results: Fifty-one percent of boosted single PI regimens (n=805) and 51.6% of boosted double PI regimens (n=183) achieved a plasma HIV RNA level of <75 copies/ml at week 12–36. In models including multiple potentially confounding variables, estimates of the relative odds of suppression on boosted double versus boosted single PI regimens ranged from 1.17 (95% CI, 0.54–2.55) to 1.33 (95% CI, 0.82–2.14).
Conclusions: We were not able to reject the null hypothesis that boosted double versus boosted single PI regimens, resulted in equivalent probabilities of virologic success.
From the aDivision of Biostatistics, School of Public Health, University of California, Berkeley, California, USA
bDivision of Infectious Disease, Center for AIDS Research, Stanford University, Palo Alto, California, USA
cClinical Trials Unit, Kaiser Permanente, San Francisco, California, USA.
Received 25 November, 2007
Revised 25 April, 2007
Accepted 27 April, 2007
Correspondence and reprint requests to Maya L. Petersen, Univ. of California, Berkeley, Earl Warren Hall #7360, Berkeley, CA 94720, USA. Tel: +1 510 642 3241; fax: +1 510 643 5163; e-mail: firstname.lastname@example.org