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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One! Two pharmaceutical giants team up to find a simpler, better way to fight HIV
From Advocate, The, 6/21/05 by Bob Adams

Treating HIV disease could become a lot easier for many people who are on a medication regimen. Two of the world's pharmaceutical giants--Bristol-Myers Squibb and Gilead Sciences--have teamed up to create the so-called holy grail of treatment: a single pill containing an entire day's worth of antiretroviral medications.

If approved by the U.S. Food and Drug Administration, the proposed once-a-day pill containing Sustiva, Viread, and Emtriva would be the simplest anti-HIV regimen available.

AIDS treatment advocates have longed for easier-to-take courses of anti-HIV drugs since the early days of combination therapy--when 25 to 30 pills a day could be typical. Even today's simplest regimens require two to four pills daily, which some experts say still makes it burdensome to achieve near-perfect adherence. And recent studies have shown that these medications can lose their effectiveness if taken less than 95% of the time.

"I personally see a lot of patients with new infections and treatment-naive patients, and people want to start with the easiest possible dosing regimen," says Tony Mills, MD, an HIV specialist in Los Angeles who is gay and HIV-positive himself. "The easier the dosing regimen, the more likely you are to be adherent. The better you adhere, the more likely it is that your viral load will remain undetectable in the long term."

BMS spokesman Eric Miller calls the first-of-its-kind collaboration between pharmaceutical rivals an "important milestone" in HIV treatment. "It grew entirely from the companies responding to meet the growing need for increased treatment options," he says.

Because each of the component drugs in the new pill have already been approved individually by the FDA, the new combination treatment could zip through the government approval process, according to the manufacturers, and hit the market as soon as the second half of 2006.

MILESTONES

1984 Researchers discover HIV; it is three years since the first U.S. AIDS cases were reported

1987 AZT is the first medication approved to treatment HIV

1995 invirase is the first protease inhibitor approved for treatment; the era of combination therapy begins

1996 Viramune, the first drug in the third class of antiretrovirals, is approved

1997 Combivir, the first pill to combine two anti-HIV medications, is approved

2000 New medication Trizivir combines three nucleoside analogs into one pill

2002 The first one-pill-a-day formulation of one antiretroviral, Sustiva, is approved

2003 Fuzeon is the first approved medication in the fusion inhibitor class

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