Pharmacokinetic-pharmacodynamic relationships between pirarubicin exposure and hematotoxicity: clinical application using only one blood sample.

The objective of the present study was to evaluate the relationship between the pharmacokinetic parameters of pirarubicin and of its metabolite doxorubicin measured in plasma and whole blood, and the hematologic toxicity of this drug, in order to evaluate the predictability of changes in white blood cells (WBC) by single measurement of drug concentrations. This pharmacokinetic-pharmacodynamic relationship was studied in a total of 45 patients with different tumor types treated by combined chemotherapy containing pirarubicin, administered as short infusion (10+/-2 min) at doses ranging from 50 to 90 mg. In 45 courses performed in 24 patients, we established the relationship between the half-product of pirarubicin level in whole blood at the end of the infusion and the duration of this infusion, which represents an estimate of the area under the time x concentration curve (AUC(PIRA,wb,ei) = C(PIRA,wb,ei) x duration of infusion/2), the age of the patients and the relative fall in WBC counts. These results allowed us to establish a predictive formula in order to anticipate the number of WBC that the patient will obtain about 12 days after treatment, at the nadir of the counting. WBCnadir = 0.032404 x Age + 2.005 + WBCinitial x e(-0.009316 x AUC(PIRA,wb,ei) + 4.202265), WBC being expressed as x 10(3) cells/microl and AUC(PIRA,wb,ei) in ng/ml x h. In a second step, the validation of the prediction was carried out in 43 courses from 21 patients treated in the same conditions, for which WBC(predicted nadir) was compared by linear regression to WBCcounted. We obtained a highly significant correlation: r = 0.656; p<0.0001). Therefore, we show in this paper that the hematological toxicity, especially the WBC nadir count, can be predicted from single-sample blood HPLC analysis. This rapid and easy prediction of leukopenia can help the clinician in anticipating important hematological toxicities and in deciding to start early prophylactic treatment with hematopoietic growth factors.