Long-term treatment with zidovudine in patients with human immunodeficiency virus (HIV)-associated thrombocytopenia: modes of response and correlation with markers of HIV replication.

The effects of zidovudine on the platelet count were studied in 152 patients with HIV-related thrombocytopenia of severe grade (platelet count < 50 x 10(9)/l) and moderate grade (platelet count < 100 and > 50 x 10(9)/l). In both groups of patients there was a significant increase in the mean platelet count from the baseline value, after 2 weeks (from 21 x 10(9)/l to 48 x 10(9)/l and from 75 x 10(9)/l to 97 x 10(9)/l) and 3 months of therapy (to 59 x 10(9)/l and to 144 x 10(9)/l). Sixty-five and 39 patients were followed up for 12 and 18 months, respectively, and the mean platelet values after 12 and 18 months of therapy were still significantly increased, compared to the respective mean baseline values, in both groups of patients. Clinical progression of the disease was observed in 23 treated patients, none of them showing concomitant reductions of the platelet number. An increase in the mean CD4+ cell count after 3 months of therapy was followed by a progressive decline in the 65 patients with a 12-month follow-up, while no significant changes of the p24 antigenemia rates were observed after 1 year of therapy in 53 patients evaluated. The long-term effects of zidovudine on the platelet count, but not on other parameters of clinical outcome, might be explained by the involvement of specific mechanisms in the pathogenesis of this kind of thrombocytopenia and of its response to zidovudine.