Serum thymidine kinase--a marker of bone marrow toxicity during treatment with zidovudine.

Serum thymidine kinase (S-TK) was measured weekly in 16 randomly selected patients with AIDS or AIDS-related complex (ARC; Centers for Disease Control group IV A or group IV C-2) who participated in a controlled study of the efficacy of zidovudine therapy. S-TK increased significantly (P less than 0.01) in the zidovudine group, whereas it remained stable in the placebo (control) group. On the basis of this observation, the value of S-TK measurements as a predictor of bone marrow toxicity during zidovudine therapy was investigated in 42 patients with AIDS or ARC who received zidovudine as part of their usual treatment. There was a significant association between S-TK, haemoglobin and neutrophil counts measured after the first 4 weeks of therapy and the risk of developing bone marrow toxicity during the following 6 months. Combined, measurements of S-TK and neutrophil counts seem to be well suited for the identification of patients who have a high probability for developing bone marrow toxicity during zidovudine treatment.