Invirase

Saquinavir, with trade name Fortovase® is a protease inhibitor used as a component of highly active antiretroviral therapy (HAART). more...

Saquinavir mesylate is a different formulation, designed to be combined with another protease inhibitor that increases the bioavailability of the saquinavir.

History

Saquinavir was the first protease inhibitor (and sixth antiretroviral) approved by the Food and Drug Administration (FDA). It was approved on December 6, 1995, as Invirase®, a poorly-absorbed hard gel capsule which quickly led to viral resistance in many of the pioneer patients.

It was approved again on Nov 7, 1997 as Fortovase®, a soft gel capsule reformulated for improved bioavailability. The manufacturer, Roche, is alleged to have rushed Invirase® to market, but the conditions that prevailed at the time were very bad and there was a lot of pressure to produce products quickly.

Method of activity

When given alone, the HIV Protease Inhibitor (HPI) saquinavir has a very low oral bioavailability. In the clinic, it was found that the oral bioavailability of saquinavir significantly increases when patients also receive the HPI ritonavir. For patients, this has the major benefit that they can take less saquinavir, while maintaining sufficient saquinavir blood plasma levels to efficiently suppress the replication of HIV.

The mechanism behind this welcome observation was not directly known, but later it was determined that ritonavir inhibits the enzyme Cytochrome P450 3A4. Normally, this enzyme metabolizes saquinavir to an inactive form, but with the ritonavir inhibiting this enzyme, the saquinavir blood plasma levels increased considerably. Additionally, ritonavir also inhibits multidrug transporters, although to a much lower extent.

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