New antiretrovirals and new combinations.

The appearance in the clinic of two to three new antiretroviral agents yearly since 1995 has permitted unprecedented advances in HIV treatment. This remarkable pace of drug development is a testimony to an extraordinary international effort involving scientists, clinicians, governments, community activists and industry dedicated to the rapid and safe development of novel therapies. New drugs present the opportunity to improve HIV therapy. They also create an enormous challenge to the clinician, who must constantly assimilate data on new drugs and incorporate this information into practical management strategies. Combination therapy has proven the most effective approach to treat HIV disease. The profound and sustained viral suppression achievable with combinations such as indinavir (IDV), lamivudine (3TC) and zidovudine (ZDV) have resulted in a dramatic shift in HIV treatment paradigms over the last year. The full potential of combination therapy with available drugs has yet to be realized as only a limited number of the possible combinations incorporating new drugs have been fully tested. Even drugs available for many years may have untapped potential. Didanosine (ddI) and stavudine (d4T), once thought to be contraindicated in combination because of their overlapping peripheral neuropathy toxicity, have proven well tolerated and effective. Combination therapy can increase antiviral suppression, prevent drug resistance, optimize drug exposure and simplify dosing, but it can also result in pharmacologic antagonism, subtherapeutic drug concentrations and unexpected toxicities. Clinical studies have confirmed in vitro studies showing pharmacologic antagonism for the combination of ZDV and d4T. Combining protease inhibitors with each other or with non-nucleoside reverse transcriptase inhibitors is complicated by effects both classes of drugs have on drug metabolism and clearance. These observations underline the importance of carefully conducted clinical studies to characterize safety, pharmacokinetics and efficacy of combination therapies. In this review, we will first summarize the clinical profile of new drugs which either became commercially available last year [nelfinavir, nevirapine, delavirdine (DLV)] or are in the late stages of clinical development (DMP-266, abacavir and 141W94). Later we will summarize new data on nucleoside, protease inhibitor and non-nucleoside reverse transcriptase combination regimens. Finally, we will briefly mention new drugs in early stages of development.