Roche has issued a letter warning that its anti-HIV medications, Invirase (saquinavir hard gel capsules) and Fortovase (saquinavir soft gel), when “boosted” by Abbott’s Norvir (ritonavir), should not be taken with the anti-tuberculosis drug rifampin, because of the risk of drug-induced hepatitis.

The Swiss company issued the warning after it conducted a Phase I study involving 28 healthy volunteers who were given 1,000mg of saquinavir boosted by 100mg of ritonavir twice daily with a 600mg daily dose of rifampin.

Just over 39% of the volunteers in the study developed significant drug-induced hepatitis, and one individual was admitted to hospital with marked transaminase elevations – such as mild liver failure.

The study was immediately discontinued, and liver function returned to normal in all the affected individuals. No deaths from the study have been reported and Roche noted that unboosted saquinavir and rifampin are also contraindicated.

Roche concluded by saying that it is collaborating closely with the US Food and Drug Administration on this issue, “and appropriate changes to the package insert will be made as soon as possible.”