Current HIV clinical trial design issues.

Abstract

Aids-free time and survival time of people with HIV infection has gradually increased since the first clinical trial of zidovudine(AZT) in 1987. This change in pattern of disease course has, however, made it difficult for current clinical trials to rely on "hard" clinical end points, such as progression to AIDS or death, to demonstrate antiretroviral efficacy. These trials must continue for a number of years and enroll large numbers of patients; as a result, maintaining patients on protocolled therapy is difficult to achieve. Furthermore, patients can be prevented from reaching clinical end points by prophylaxis of opportunistic infections. Combined with the move toward treating individuals earlier in the course of infection, current clinical trials using "hard" clinical end points are unlikely to demonstrate drug efficacy. The concept of using "soft" clinical end points and laboratory end points such as decline in CD4 cell count to a threshold value, was first introduced in study EACG 020 of patients with early stage infection, and made it possible for this study to demonstrate the efficacy of AZT in this patient population. Further accurate markers of disease progression are required for current clinical trials. There is growing consensus that the primary end point of any antiviral drug study should be the effect of the drug on the virus itself. It is now possible to quantify viral burden and to assess the amount of virus present in different tissues. To validate viral load as a marker of disease progression, it is necessary to achieve a profound and long-term reduction in viral load. It is very likely that this will be achieved only in studies of multiple combination therapy at early stages of infection. Moreover, clinical trials are required to validate the use of viral load. In the meantime, regulatory authorities should be encouraged to license drugs on the basis of viral load data with the provision of intense post-licensing follow-up.