New London, CT -- Pfizer Inc. said today that it has discontinued clinical development on capravirine, a phase 2 HIV/AIDS drug in a class known as non-nucleoside reverse transcriptase inhibitors (NNRTIs). Pfizer has been developing capravirine for patients with HIV/AIDS who have failed on currently available antiretroviral therapies.
Pfizer based the decision on results of two phase 2b studies, several drug interaction studies, and consultations with key HIV stakeholders. Neither of the phase 2b studies showed a statistically-significant difference between standard triple-drug HIV therapies and the same therapy with capravirine. The first of these studies was published recently at the 12th Annual Conference on Retroviruses and Opportunistic Infections in February 2005 and the second will be submitted for publication at an upcoming HIV/AIDS conference in the near future. Furthermore, several pharmacology studies showed that capravirine could have complex drug-drug interactions with other HIV therapies. These complex interactions make capravirine difficult to use in treatment-experienced patients whose regimen can include five or more different HIV drugs.
"This decision is disappointing for all concerned with the treatment of HIV," said John LaMattina, president, Pfizer Global Research and Development. "There is a great unmet medical need for this patient population. Data from these phase 2b studies show that capravirine does not offer substantial enough benefit over already available therapies. For that reason we can't justify continued development of this compound. We will redirect resources to progress our other HIV/AIDS therapies."
Discovered in the mid-1990s by Shionogi & Co Ltd., capravirine targets HIV that is resistant to currently available antiretrovirals and other NNRTIs. Earlier research had shown the drug to be potent against both "wild-type" and drug-resistant HIV in the laboratory. Pfizer licensed capravirine from Shionogi in 1998, began its development and has been evaluating its use in combination with other therapies against drug-resistant HIV.
"The effort to develop this drug addressed an unmet medical need so it is disappointing that the study results failed to show sufficient efficacy to continue," said Doug Richman, M.D., Professor of Pathology and Medicine, University of California, San Diego.
The discontinuation process will begin immediately. Pfizer said it will ensure that capravirine study patients have continued access to appropriate therapy while their managing physicians make alternative provisions.
Pfizer remains committed to bringing meaningful improvement to the lives of people living with HIV/AIDS and those at risk around the world. Pfizer HIV/AIDS research teams in La Jolla, California and Sandwich, England are discovering and developing novel HIV/AIDS medicines. Maraviroc, a CCR5 co-receptor antagonist, is in advanced stages of global clinical development.