From Dr N. Warwick, MB, BS
SIR,—Regarding the news item on liver toxicity of AIDS drugs (PJ, January 8, p48), Abbott Laboratories is now in a position to make the following company comment.
Abbott has been monitoring and reporting the results of abnormalities in liver function tests associated with the use of Norvir (ritonavir) to regulatory authorities throughout the product's history.
The summary of product characteristics for ritonavir warns of the possibility of an increased risk for transaminase elevations in patients with underlying hepatitis B or C and advises caution when administering ritonavir alone or in combination with other antiretrovirals to patients with pre-existing liver disease, liver enzyme abnormalities, or hepatitis. Ritonavir is contraindicated in patients with severe hepatic insufficiency. Ritonavir is used in combination with other antiretroviral agents, which also may contribute to abnormal liver function test results.
In the three controlled clinical studies of more than 900 patients reported in ritonavir's "label", the incidence of abnormalities in liver function was less than 10 per cent. This number is less than the 30 per cent reported in JAMA. Additionally, the study published in JAMA was a prospective chart review, not a controlled clinical trial. Many of the patients treated with protease inhibitors had advanced HIV disease (as reflected by low T-cell counts) and almost half were co-infected with hepatitis C. Among the 298 patients reported, only 50 patients were treated with ritonavir.
Nick Warwick
Medical Affairs Manager, Abbott Laboratories, Maidenhead, Berkshire