HIV This Week

Paltiel AD, Freedberg KA, Scott CA, Schackman BR, Losina E, Wang B, Seage Iii GR, Sloan CE, Sax PE, Walensky RP. HIV Preexposure Prophylaxis in the United States: Impact on Lifetime Infection Risk, Clinical Outcomes, and Cost-Effectiveness. Clin Infect Dis. 2009;48(6):806-815.

The combination of tenofovir and emtricitabine shows promise as HIV preexposure prophylaxis (PrEP). Paltiel and colleagues sought to forecast clinical, epidemiologic, and economic outcomes of PrEP, taking into account uncertainties regarding efficacy, the risks of developing drug resistance and toxicity, behavioural disinhibition, and drug costs. They adapted a computer simulation of HIV acquisition, detection, and care to model PrEP among men who have sex with men and are at high risk of HIV infection (i.e., 1.6% mean annual incidence of HIV infection) in the United States. Base-case assumptions included 50% PrEP efficacy and monthly tenofovir-emtricitabine costs of $753. They used sensitivity analyses to examine the stability of results and to identify critical input parameters. In a cohort with a mean age of 34 years, PrEP reduced lifetime HIV infection risk from 44% to 25% and increased mean life expectancy from 39.9 to 40.7 years (21.7 to 22.2 discounted quality-adjusted life-years). Discounted mean lifetime treatment costs increased from $81,100 to $232,700 per person, indicating an incremental cost-effectiveness ratio of $298,000 per quality-adjusted life-year gained. Markedly larger reductions in lifetime infection risk (from 44% to 6%) were observed with the assumption of greater (90%) PrEP efficacy. More-favourable incremental cost-effectiveness ratios were obtained by targeting younger populations with a higher incidence of infection and by improvements in the efficacy and cost of PrEP. PrEP could substantially reduce the incidence of HIV transmission in populations at high risk of HIV infection in the United States. Although it is unlikely to confer sufficient benefits to justify the current costs of tenofovir-emtricitabine, price reductions and/or increases in efficacy could make PrEP a cost-effective option in younger populations or populations at higher risk of infection. Given recent disappointments in HIV infection prevention and vaccine development, additional study of PrEP-based HIV prevention is warranted.

Editors’ note: To date, evidence from animal studies indicates promise for pre-exposure prophylaxis (PrEP) but none of the eight oral and/or topical PrEP trials planned or currently underway in a variety of populations have reported results. Based on current treatment costs for tenofovir-emtricitabine and conservative estimates of efficacy, PrEP is an unattractive option from a US-based cost-effectiveness perspective but reduced costs and increased efficacy would improve the incremental cost-effectiveness ratio (dollars per quality adjusted life years [QALYs] gained). Now let’s get some real data to inform such modelling!