Highly active antiretroviral therapy (HAART) has helped prolong survival in people with HIV/AIDS (PHAs). HAART regimens, particularly those containing protease inhibitors, can have a range of side effects, including nausea, vomiting and diarrhea, as well as food and water restrictions. In an effort to avoid these difficulties, some PHAs may replace or switch their protease inhibitor(s) with a non-nucleoside analogue (non-nuke), such as one of the following:

• delavirdine (rescriptor)
• efavirenz (Sustiva, Stocrin)
• nevirapine (Viramune)

Questions remain about what happens after PHAs make their switch, specifically:

• Will viral load continue to remain suppressed?
• Will PHAs be able to tolerate efavirenz-containing regimens?

To answer these questions, researchers in Switzerland conducted a study.

Study details

The researchers sorted and analysed medical records in their database, called the Swiss HIV Cohort. They collected data on the following groups of PHAs who had similar profiles:

• 184 switchers — these were PHAs who switched from protease-inhibitor-based regimens to efavirenz-based regimens
• 368 non-switchers — these were PHAs who continued to use protease inhibitors (PIs)

The profile of the switchers was as follows:

• they had previously used the PIs indinavir (Crixivan) or nelfinavir (Viracept) or ritonavir (Norvir)
• they switched because of intolerance or toxicity caused by the PI
• they stopped using the PI once they switched to efavirenz
• 75% of subjects had been previously exposed to anti-HIV drugs for about 2.5 years before switching to efavirenz
• 30% female, 70% male
• an average of 503 CD4+ cells
• an average viral load of fewer than 400 copies

Results – viral load

After switching, those PHAs who had their viral load rise above the 1,000 copy mark were considered by their doctors to have had "virological failure." The risk of PHAs developing virological failure after one year in each of the two study groups was as follows:

• switched to efavirenz – 9%
• remained on PIs – 27%

This difference was statistically significant; that is, not likely due to chance alone.

Results – CD4+ cell counts

There were no significant differences in CD4+ cell counts between switchers and non-switchers "at any time" during the study.

Efavirenz problems

Subjects who were injection-drug users (IDUs) were more likely than non-IDUs to stop using efavirenz, particularly during the first month after switching. For 73% of IDUs who did stop during this time, the reasons for doing so were "intolerance or side effects."

When researchers analysed the rate at which subjects stopped using PIs, IDUs were no more likely to stop using PIs than other groups of PHAs.

The study authors concluded that data from this study suggests that replacing a PI with efavirenz can benefit treatment-experienced PHAs, particularly those who are not IDUs.

REFERENCE

Hirschel B, Flepp M, Bucher HC, et al. Switching from protease inhibitors to efavirenz: differences in efficacy and tolerance among risk groups: a case-control study from the Swiss HIV cohort. AIDS 2002;16(3):381-385.

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