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Heat-Stable Formulation of Norvir Appears Likely

By Paul Dalton

September 2008

In a late-breaker session at the International AIDS Conference, Abbott announced progress on their long-delayed heat stable form of their booster, Norvir (ritonavir). Now several years after their successful development of a heat stable form of Kaletra (lopinavir + ritonavir), this news is welcomed.

Norvir was originally developed as a protease inhibitor, but it fell out of use due to its high side effect rates and manufacturing problems. It continued to be used in low doses to boost the levels of other protease inhibitors. Its current formulation requires refrigeration. While this is an inconvenience for some, more importantly it is a major barrier to delivering boosted protease inhibitors to resource-poor areas of the world, where maintaining the necessary "cold chain" isn't possible.

In 2005, Abbott gained approval for a heat stable formulation of Kaletra. They used a technology called Meltrex (melt extrusion) to reformulate Kaletra. Ever since people have been wondering when, and even if, Abbott would do the same for Norvir.

Earlier this year Project Inform learned Abbott had made significant strides in developing their Meltrex formulation of Norvir. The study presented in Mexico City showed that the Meltrex Norvir is bioequivalent to the older soft gel formulation. This means that the two formulations achieve nearly the same levels in the body. They also showed similar rates and severity of side effects. Because the soft gel formulation of Norvir is already FDA approved, Abbott only needs to prove bioequivalence and safety to gain FDA approval to market the new formulation.

Abbott announced plans to file with the FDA by the end of 2008. The FDA then has 6 months to issue a ruling, meaning this formulation is likely to be on pharmacy shelves towards mid-2009.

This is welcome albeit long overdue news. Many have openly questioned the reasons for the long delay between the Meltrex formulations of Kaletra and Norvir. Was Abbott trying to protect the market position of Kaletra, by keeping it as the only boosted PI that didn't require refrigeration? Abbott took pains to detail the missteps and formulation failures it encountered along the way, showing pictures of grossly swollen tablets for illustration.

It's noteworthy that other companies, including Pfizer and Gilead, are now developing their own boosters. Is the specter of impending competition the real motive? Maybe, but it will be some years before any new booster makes it to market. Whatever the back-story, a heat stable form of Norvir is indeed welcome news, particularly for expanding treatment into resource-poor areas.

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