Head-to-Head Study of Two Protease Inhibitors

Results from a study comparing the recently approved protease inhibitor lopinavir (Kaletra) to nelfinavir (Viracept) as first-line therapy were reported at a major International AIDS conference in Glasgow, Scotland. Lopinavir includes a new protease inhibitor along with a small dose of ritonavir in a single capsule. Seven hundred and fifty-three people with average viral loads of about 80,000 copies HIV RNA and CD4+ cell counts averaging 260 received either lopinavir or nelfinavir in combination with d4T (stavudine, Zerit) and 3TC (lamivudine, Epivir). After forty-eight weeks the results were as follows, using a strict "intent to treat" analysis:

Significantly more people receiving lopinavir achieved viral suppression below 400 copies and 50 copies, though there were no differences between the two groups in the magnitude of CD4+ cell increases. There were no significant differences in side effects, including changes in triglyceride levels, between the two groups although fewer people receiving lopinavir discontinued drug primarily due to rebound in viral load (virological failure).

These results are not completely unexpected. Previous studies have shown lopinavir to have very potent activity against HIV, even among people who have previously received protease inhibitors. Additionally there have been concerns about the long-term potency of nelfinavir.

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