This antiviral offers new option to HIV patients

August 7, 2006

Despite the accelerating rate of HIV and AIDS on every continent, "only 12% of people in need of antiretroviral therapies in low- and middle-income countries are receiving them," said United Nations Secretary-General Kofi Annan in an opening address at a high-level conference on AIDS, held recently in New York. Thus, with treatment and prevention efforts being dubbed by Annan as "insufficient," Prezista (darunavir, Tibotec Therapeutics), the new protease inhibitor (PI), is being launched into an HIV market fraught with problems such as drug accessibility shortfalls and drug-resistant HIV.

Darunavir, indicated for the treatment of HIV in antiretroviral treatment-experienced adult patients, appears to have been designed specifically to tackle viral strains that are resistant to one or more PIs. Chemically similar to amprenavir, darunavir has been shown to be "extremely" potent against both wild-type (wt) and multidrug-resistant (MDR) viruses in vitro as well as in vivo. Ron Falcon, M.D., senior medical director at Tibotec Therapeutics, attributes this characteristic to the agent's ability to "be flexible enough to fit into a mutated protease binding site, and then to bind very tightly once it's in there."

Darunavir is intended to be given with ritonavir, which slows clearance of darunavir, "increasing its exposure 14-fold," noted Falcon. The new PI also appears to work best when given in combination with the fusion inhibitor Fuzeon (enfuvirtide, Roche). In pivotal clinical studies, up to two-thirds of patients with extensive prior exposure to anti-HIV drugs who were given darunavir/ritonavir in combination with enfuvirtide achieved undetectable levels of HIV.

In regard to its safety profile, darunavir, when used in combination with ritonavir, is most commonly associated with diarrhea, nausea, and headache. Approximately 7% of patients on this combination experienced skin rashes, which were generally mild to moderate, self-limiting, and maculopapular; rarely, there were cases of severe skin rashes, including erythema multiforme and Stevens-Johnson syndrome. Some patients experienced fever and elevations of transaminases.

Darunavir certainly appears to address the resistance issue that is so inherent to HIV management in this day and age. But how financially accessible is this newest PI? Not very, according to the AIDS Healthcare Foundation (AHF), the largest AIDS organization in the United States. AHF recently criticized Tibotec in anticipation of its steep pricing for darunavir, which will reportedly be $25 a day at wholesale cost.

THE AUTHOR is a clinical writer and hospital pharmacist in New Jersey.