Protease Inhibitors Less Effective on HIV Types A,C, Study Shows

Protease inhibitors, a class of HIV drugs used in combination therapy, are not as effective against the A and C subtypes of HIV, the two strains most commonly found in Africa as they are against Subtype B, Reuters Health reports. The drugs fight HIV by "blocking the action" of protease, an enzyme needed by the virus to replicate itself. A study published in the May 22 issue of the Proceedings of the National Academy of Sciences measured the "activities" of protease enzymes against four different protease inhibiting drugs -- indinavir, saquinavir, nelfinavir and ritonavir -- and found that protease taken from the A and C strains of HIV were "better able to perform their normal functions in the presence" of the drugs. However, "[w]e are not saying that the therapies do not work" against these subtypes, Dr. Ernesto Freire of Johns Hopkins University said. The drugs, which were designed to work against HIV-B, the most common HIV subtype found in the United States, just do not work as well against the African strains, he said, adding that "other factors" play into the drugs' effectiveness. This finding "highlight[s] the importance" of testing drugs on patients with various strains of HIV, the study reports, especially because patients with non-B subtypes have already begun reporting drug failures. Freire hopes to develop a "second-generation" of protease inhibitors to battle subtypes A and C and strains of subtype B that have grown resistant to the current drugs (McKinney, Reuters Health, 5/17).