Project Inform - September, 1998

A small study of 20 people who were virologically failing a regimen containing indinavir showed that the addition of a NNRTI (non-nucleoside reverse transcriptase inhibitor) to a three-drug regimen results in renewed potent antiviral activity. People with an average CD4+ count of 290 cells and HIV RNA levels of about 20,000 copies received one of two regimens:

• nelfinavir (Viracept^®) + soft gel saquinavir (Fortovase^®) + abacavir + another nucleoside analogue drug, or
• nelfinavir + soft gel saquinavir + abacavir + nevirapine (Viramune^®)

The doses used in this study were 1,250mg twice a day (2,500mg total daily dose) of nelfinavir, 1,200mg twice a day (2,400mg total daily dose) of saquinavir, 300mg twice a day (600mg total daily dose) of abacavir and 200mg twice a day (400mg total daily dose) of nevirapine. None of the participants had previously been on any of the four drugs in either regimen. The results after 20 weeks are shown in Table 1 below.

Table 1 : Salvage Study Results

NFV=nelfinavir SQV=saquinavir ABA=abacavir NVP=nevirapine
NARTI=nucleoside analogue reverse transcriptase inhibitor

This study shows that simply switching to a dual protease inhibitor regimen may not be adequate to regain control of viral replication, probably due to the presence of cross-resistance between protease inhibitors. The study confirms that the best results are achieved when at least two new potent drugs are started simultaneously. In this instance, it seems clear that the addition of the NNRTI provided substantially more benefit than simply switching to two protease inhibitors. Phenotypic resistance testing was done prior to study entry and was found to be highly predictive of an antiviral response. In other words, those with demonstrated phenotypic resistance to the drugs used were least likely to see decreases in HIV levels, where as those without resistance were more likely to see decreases in HIV levels. People sensitive to two or three of the drugs at study entry experienced sustained HIV suppression whereas people who were sensitive to 0 or 1 drug experienced either no or only a transient reduction in HIV suppression.

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The original of this article can be found at http://www.projinf.org/pub/25/antiviral.html