Two formulations of saquinavir are currently manufactured — Invirase, the original hard-gel form, and Fortovase, the newer soft-gel form. A capsule of each product contains 200 mg of saquinavir. Results from a very small study suggest that saquinavir (either Invirase or Fortovase) 1,000 mg, in combination with ritonavir 100 mg, both taken twice daily, leads to roughly equivalent levels of saquinavir in the blood. So researchers in Berlin decided to conduct a larger study.

Study details

Twenty-four healthy, HIV negative subjects were divided into two groups and given one of the following combinations taken twice daily for one week:

• Invirase 1,000 mg and ritonavir 100 mg
• Fortovase 1,000 mg and ritonavir 100 mg

At the end of that time, subjects were switched to the combination they had not yet received.

Results

• In analysing blood samples, technicians found that subjects who received Invirase had significantly higher levels (about 35% to 40%) of saquinavir in their blood than those who received Fortovase.
• The combination of Invirase/ritonavir was better tolerated than Fortovase/ritonavir, with fewer reports of diarrhea and bloating.

The research team suggests that people with HIV/AIDS who are receiving Fortovase/ritonavir and who have diarrhea, bloating and other gastrointestinal (GI) side effects may benefit from a switch to Invirase/ritonavir.

Why was Invirase better tolerated?

Fortovase contains an ingredient called capmul which is supposed to help dissolve and disperse saquinavir rapidly once it is in the digestive tract. Some researchers suspect that it is the presence of capmul which makes Fortovase users more prone to GI side effects. This is not the first time that researchers have noted that high doses of Invirase/ritonavir are better tolerated than Fortovase/ritonavir. We wonder if some doctors may begin switching their patients who are experiencing GI toxicity on Fortovase to Invirase.

REFERENCES

1. Kurowski M, Sternfeld T, Hill A, et al. Comparative pharmacokinetics and short-term safety of Fortovase/ritonavir and Invirase/ritonavir 1000 mg/100 mg BID. 3rd International Workshop on Clinical Pharmacology of HIV Therapy, 11-13 April, 2002, Washington D.C. Abstract 7.17.

2. Montaner JSG, Saag M, Barylski C, et al. FOCUS study: saquinavir QD regimen versus efavirenz QD regimen: 24-week analysis in HIV-infected patients. 41st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), 16-19 December, 2001, Chicago. Abstract I-669.

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