Pharmacokinetics of cisplatin given at a daily low dose as a radiosensitiser

A total of 25 patients with inoperable cervical cancer were treated by daily radiotherapy (2 Gy); sensitisation was obtained by administration of 5 mg cisplatin 30 min before each irradiation session. The total cumulative dose of cisplatin varied between 50 and 150 mg. A complete kinetic profile (0-24 h) of platinum (Pt) was established after the first dose and at the end of treatment for 22 patients. Pt was quantified by atomic absorption spectrophotometry using Zeeman-effect background correction for trace analysis. The total Pt AUC0-24h increased from 1.53 +/- 0.77 to 7 +/- 3.55 micrograms.h.ml-1 between the start and the end of treatment (P less than 0.001). Ultrafilterable Pt (Pt UF) rose from 0.079 +/- 0.038 to 0.138 +/- 0.095 microgram.h.ml-1 (P less than 0.01). Elimination half-lives were unchanged for total Pt but rose for Pt UF; these kinetic modifications in Pt UF did not correlate with any significant change in individual serum creatinine levels. No clear correlation was found between the cumulative cisplatin dose and tumor levels measured in 13 patients, and the tumor cisplatin dose did not correlate with response to treatment. Patients with hematological toxicity were characterised by an increase in their residual Pt UF level during treatment. Overall, our findings strengthen the notion of Pt UF kinetic variability during repeated treatment.