Once daily fos-amprenavir equal to nelfinavir

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Once daily dosing of fos-amprenavir, boosted with ritonavir, shows equivalent antiviral effect to nelfinavir when either drug is combined with abacavir and 3TC, according to 48 week results of the SOLO study presented yesterday at the Sixth International Congress on Drug Therapy in HIV Infection, Glasgow.

The SOLO study recruited 660 individuals in Europe and North America, and participants were randomised to receive either 1400mg of fos-amprenavir (the pro-drug of amprenavir, also known as GW433908), boosted with 200mg of ritonavir, dosed once daily, or 1250mg of nelfinavir, dosed twice daily. All participants received abacavir and 3TC twice daily.

At baseline, the median viral load was 4.78 log copies/ml in the fos-amprenavir group and 4.83 log copies/ml in the nelfinavir group, with 42% and 44% respectively having viral load above 100,000 copies/ml. 19% of the fos-amprenavir group and 21% of the nelfinavir group had baseline CD4 cell counts below 50 cells/mm3.

Glossary

cholesterol

A waxy substance, mostly made by the body and used to produce steroid hormones. High levels can be associated with atherosclerosis. There are two main types of cholesterol: low-density lipoprotein (LDL) or ‘bad’ cholesterol (which may put people at risk for heart disease and other serious conditions), and high-density lipoprotein (HDL) or ‘good’ cholesterol (which helps get rid of LDL).

log

Short for logarithm, a scale of measurement often used when describing viral load. A one log change is a ten-fold change, such as from 100 to 10. A two-log change is a one hundred-fold change, such as from 1,000 to 10.

boosting agent

Booster drugs are used to ‘boost’ the effects of protease inhibitors and some other antiretrovirals. Adding a small dose of a booster drug to an antiretroviral makes the liver break down the primary drug more slowly, which means that it stays in the body for longer times or at higher levels. Without the boosting agent, the prescribed dose of the primary drug would be ineffective.

equivalence trial

A clinical trial which aims to demonstrate that a new treatment is no better or worse than an existing treatment. While the two drugs may have similar results in terms of virological response, the new drug may have fewer side-effects, be cheaper or have other advantages. 

antiviral

A drug that acts against a virus or viruses.

463 patients who had completed 48 weeks of treatment were reported in this analysis, which showed that 68% of the fos-amprenavir group and 65% of the nelfinavir group had viral load below 400 copies/ml at week 48 by intent to treat, missing equals failure analysis. A subgroup analysis by baseline viral load showed that amongst people with baseline viremia above 500,000 copies/ml (51 patients in the fos-amprenavir group and 47 patients in the nelfinavir group) 71% of the fos-amprenavir group and 53% of the nelfinavir group had viral load below 400 copies/ml at week 48. This result was not subjected to significance testing so it does not necessarily show that fos-amprenavir was superior to nelfinavir in patients with high baseline viral load. However, a similar trend was apparent in patients with baseline CD4 cell counts below 50 cells/mm3 (69% vs 54%).

Data on resistance were the subject of controversy in the question and answer session following the presentation. Thirty two virological failures were detected in the fos-amprenavir group and 54 in the nelfinavir group, and whilst 30 of the nelfinavir had primary protease mutations, none of the fos-amprenavir group had such mutations. Similarly, whilst 31 of the nelfinavir group had nucleoside analogue associated mutations, only three of the fos-amprenavir group had such mutations.

Prof. Joep Lange found these results hard to believe. “This suggests either that people were not taking the drugs properly in the fos-amprenavir group or else the samples weren’t taken properly. Normally you would expect to see the 184 mutation [associated with 3TC resistance]” he told the session.

Grade 3 and 4 triglyceride elevations were more significantly common in the fos-amprenavir group than in the nelfinavir group (6% vs 2%), but grade 3 and 4 cholesterol and glucose elevations were very infrequent, occurring in less than 1% of patients. However, modest increases in total cholesterol and LDL cholesterol were seen in both groups by week 12, with the mean level remaining below 160mg/dl at week 48. The proportion of patients in each arm who experienced elevations above 160mg/dL was not reported.

Diarrhoea was more common in the nelfinavir group (16% vs 9%, p=0.008), but nausea and vomiting were reported at similar levels in the two groups (around 5 –7 %).

References

Shurmann D et al. Efficacy and safety of GW433908/ritonavir once daily in therapy-naive subjects, 48 weeks results: The SOLO study. Sixth International Congress on Drug Therapy in HIV Infection, Glasgow, abstract PL14.4, 2002.