Saquinavir

Saquinavir is an antiretroviral drug used in HIV therapy. It falls in the protease inhibitor class. Two formulations have been marketed:

• a hard-gel capsule formulation of the mesylate, with trade name Invirase®, which requires combination with ritonavir to increase the saquinavir bioavailability;

• a soft-gel capsule formulation of saquinavir, with trade name Fortovase®.

Both formulations are generally used as a component of highly active antiretroviral therapy (HAART).

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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. 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.

It was approved again on Nov 7, 1997 as Fortovase®, a soft gel capsule reformulated for improved bioavailability. Roche announced in May 2005 that, owing to reduction in demand, Fortovase® would cease being marketed early in 2006 in favour of Invirase® boosted with ritonavir. ^[1]

Mode of action

Saquinavir is a protease inhibitor. Proteases are enzymes that cleave protein molecules into smaller fragments. HIV protease is vital for both viral replication within the cell and release of mature viral particles from an infected cell. Saquinavir inhibits both HIV-1 and HIV-2 proteases.

Toxicity

The most frequent adverse events with saquinavir in either formulation are mild gastrointestinal symptoms, including diarrhoea, nausea, loose stools & abdominal discomfort. Invirase is better tolerated than Fortovase.

Bioavailability and drug interactions

Saquinavir, in the Invirase® formulation, has a low and variable oral bioavailability, when given alone. The Fortovase® formulation at the standard dosage delivers approximately eightfold more active drug than Invirase®, also at the standard dosage.^[2]

In the clinic, it was found that the oral bioavailability of saquinavir in both formulations significantly increases when patients also receive the PI 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 cytochrome P450 3A4 isozyme. 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.

Unlike other protease inhibitors, the absorption of saquinavir seems to be improved by omeprazole.^[3]

References

1. ^ Withdrawal of Fortovase (PDF)
2. ^ Fortovase^TM (saquinavir) soft gelatin capsules. Product information (November 1997)
3. ^ Winston A, Back D, Fletcher C, et al. (2006). "Effect of omeprazole on the pharmacokinetics of saquinavir-500 mg formulation with ritonavir in healthy male and female volunteers". AIDS 20 (10): 1401–6.

Further reading

• Cohen Stuart JW, Schuurman R, Burger DM, et al. (1999) Randomized trial comparing saquinavir soft gelatin capsules versus indinavir as part of triple therapy (CHEESE study). AIDS 13:F53-58

• Dragsted UB, Gerstoft J, Pedersen C, et al. (2003) Randomized trial to evaluate indinavir/ritonavir versus saquinavir/ritonavir in human immunodeficiency virus type 1-infected patients: the MaxCmin 1 Trial. J Infect Dis 188:635-642