Important note: Information in this article was accurate in May 2002. The state of the art may have changed since the publication date. 
A team of Australian, Dutch and Thai researchers has been testing a combination of the soft-gel formulation of saquinavir (Fortovase) 1,600 mg in combination with ritonavir 100 mg, both protease inhibitors taken once daily. Taken in this way, ritonavir greatly increases saquinavir levels in the blood and prolongs the time that saquinavir remains in circulation. According to their results, after six months of observating 69 HIV positive subjects who were taking this combination of protease inhibitors together with two nukes (nucleoside reverse transcriptase inhibitors, or NRTIs), this regimen was able to suppress levels of HIV to fewer than 50 copies in the blood of 93% of subjects. In the remaining subjects, viral load remained below the 300 copy mark. This boosted regimen of saquinavir was associated with a significant increase in CD4+ cells.
As mentioned in recent CATIE News stories, the hard-gel form of saquinavir, sold under the brand name Invirase, appears to cause fewer side effects — diarrhea, nausea, bloating — than the soft-gel fomulation, sold under the brand name Fortovase. Invirase may also have other advantages, including the following:
To find out if once-daily saquinavir levels are any different when taken as Invirase or Fortovase, both formulations were tested in HIV positive Thai subjects.
Researchers randomly assigned 13 subjects (6 female, 7 male), who were already receiving Fortovase/ritonavir (1,600 mg/100 mg) once daily along with two nukes, to the following:
Before entering the study, subjects had at least 351 CD4+ cells and their viral load was below the 50 copy mark.
Overall, subjects who received Invirase had slightly higher levels of saquinavir in their blood than when they received Fortovase. Two subjects who received Invirase and four who received Fortovase developed less-than-adequate levels of saquinavir in their blood toward the end of a 24-hour period. There was no difference in ritonavir levels when subjects were taking Invirase or Fortovase.
The researchers suspect that higher levels of saquinavir that occur when Invirase is taken happen because the absorption of Invirase (hard-gel capsules) is slower, increasing the time that Invirase can be boosted by ritonavir.
The researchers also noted that saquinavir levels seen in this study were similar to those seen in other studies where saquinavir/ritonavir was taken in a dose of 1,000 mg/100 mg twice daily.
REFERENCES
1. Cardiello PG, van Heeswijk RP, Hassink EA, et al. Simplifying protease inhibitor therapy with once-daily dosing of saquinavir soft-gelatin capsules/ritonavir (1600/100 mg): HIVNAT 001.3 study. Journal of Acquired Immune Deficiency Syndromes 2002;29(5):464-470.
2. Cardiello P, Monhaphol T, Mahanontharit A, van Heeswijk RP, et al. Pharmacokinetics (PK) of once-daily saquinavir-hard gel caps and saquinavir-soft gel caps boosted with ritonavir in HIV-1+ Thai patients: HIV NAT001.4 substudy. 3rd International Workshop on Clinical Pharmacology of HIV Therapy, 11-13 April, 2002, Washington D.C. Abstract 1.2.
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