Approaches to interferon combination therapy in the treatment of AIDS.

High-dose interferon alfa (IFN alfa) therapy induces an overall response rate of 25% to 30% in unselected patients with acquired immunodeficiency syndrome (AIDS)-related Kaposi's sarcoma. Up to 50% of patients with relatively preserved immune reactivity respond to treatment. However, when dosages of 20 x 10(6) units or more per day are used to induce responses, constitutional and hematologic side effects may be significant. Therefore, efforts are being made to lower the effective dose of IFN alfa. One effort involves combining IFN alfa with zidovudine (AZT; Retrovir; Burroughs Wellcome, Research Triangle Park, NC). These agents act synergistically to block the multiplication of human immunodeficiency virus (HIV) in vitro. The drugs act at different points in the HIV multiplication cycle, which may explain their synergistic interaction. In addition, AZT enhances certain immune functions that have been correlated with a positive IFN alfa response. Preliminary clinical trials indicate that antitumor responses in Kaposi's sarcoma are seen with dosages of IFN alfa as low as 4.5 x 10(6) units per day when combined with AZT. However, the combination of IFN alfa and AZT may also produce dose-limiting hematologic side effects; these effects may limit the usefulness of the drug combination. Strategies for ameliorating these toxicities through the use of additional agents are discussed.