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ART/PrEP combo lowered HIV incidence, increased drug resistance

Issue: March 2011

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BOSTON – Antiretroviral therapy in combination with pre-exposure prophylaxis may likely have a significant impact on the prevention of HIV when compared with either strategy alone. However, overlapping agents may increase drug resistance from antiretrovirals, according to Ume Abbas, MD.

Abbas, of the department of infectious disease at the Cleveland Clinic, and colleagues developed and assessed a detailed mathematical model that imitated the HIV epidemic in South Africa to predict the combined impact of ART and PrEP rollout on the spread of HIV and drug resistance between 2012 and 2022.

The model incorporated heterogeneity in sexual behavior, HIV transmission, disease progression, and emergence of drug resistance. Three different scenarios were simulated in the study: ART alone, PrEP alone, and ART and PreP rollout combined. The key model outputs included incidence and prevalence of HIV, cumulative new infections prevented, prevelance of HIV drug -resistance and the ratio of infections prevented to resistant cases.

According to Abbas, ART alone initiated at CD4 counts less than 200 cells/mL with 80% coverage maintained for 10 years will prevent about 700,000 new infections, but for every five infections prevented, one case of resistance will be found.

When assuming 70% PrEP efficacy, 80% adherence and 50% coverage, results from the model's optimistic PrEP scenario indicated a decrease of almost 800,000 new infections with only one case of resistance per 15 infections prevented. When ART was combined with PrEP, 1.2 million infections were prevented with about 50,000 more cases of drug-resistance compared with ART alone.

Data from the model's pessimistic scenario (50% PrEP efficacy, adherence and coverage with PrEP dropout rate of 20% per year), indicated only a modest increase in the prevalence for drug-resistance and infections prevented with ART and PrEP vs. ART alone. However, when inadvertent PrEP use (in both optimistic and pessimistic PrEP plus ART scenarios) was assumed among previously infected persons, there was a significant increase in drug-resistance.

“The model predicts that ART will contribute more to drug resistance than PrEP,”Abbas said. “However, in persons who are already infected, but unaware of their status and inadvertently start using PrEP, than drug resistance from PrEP could rise significantly. Non-overlapping antiretrovirals for ART and PrEP are necessary as the use of the same therapies for both purposes will increase the prevalence of drug resistance.” – by Ashley DeNyse

For more information:

• Abbas U. #98LB. Presented at: 18th Conference on Retroviruses and Opportunistic Infections; Feb. 27-March 3, 2011; Boston.

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