The myelotoxicity of carboplatin is influenced by the time of its administration

Previous studies have demonstrated that there are circadian rhythms in susceptibility to a range of commonly used cytotoxic drugs. In this study we have compared the pharmacokinetics and myelotoxicity of carboplatin administered at 18.00 and 06.00 in random order in patients with advanced ovarian carcinoma. Carboplatin treatment at 06.00 is associated with significantly greater thrombocytopenia than at 18.00 (platelet nadir 95,000 versus 180,000, p less than 0.05). There was no pharmacokinetic difference in the patients' handling of ultrafilterable platinum therefore it is possible that there is an intrinsic rhythm of susceptibility of bone marrow to carboplatin.