How to predict carboplatin clearance from standard morphological and biological characteristics in obese patients

Background. We previously proposed a formula to predict carboplatin clearance (CL) from four patient characteristics: plasma creatinine level, body weight: age, and sex (J Natl Cancer Inst 1995; 87: 573). Its accuracy was studied in a subpopulation of obese patients. Patients and methods. Twenty-five patients (16 male and 9 female, 23 to 82 years old) were studied. They were 20% to 67% (median 36%) over the ideal weight which was calculated according to the Lorentz equation. Their actual CL was obtained individually by the Siphar program. The pharmacokinetic population program NONMEM was used to determine the best value of substitution for weight in the formula. Results. By using the actual weight, CL was significantly overpredicted (by more than 20% for 7 of 25 patients). By using the mean value between the ideal and the actual weight, a good prediction of CL was obtained: the percentage of error ranged from -21% to +22%. Conclusion: The formula is applicable to obese patients if both ideal and actual weights are taken into account.