Total body clearance and platinum accumulation in patients treated with cis-dichlorodiammine platinum (II)

Clinical pharmacokinetics of carboplatin

The pharmacokinetics of carboplatin were investigated in cancer patients after single, IV infusion doses of 75, 150, 247.5, 300, 375, and 450 mg/m2. Total plasma and urine platinum and plasma ultrafilterable platinum concentrations were determined by atomic absorption spectrometry. Carboplatin was analyzed in plasma by a specific high-performance liquid chromatography (HPLC) procedure. Total plasma platinum, which represented free carboplatin, protein-bound platinum and metabolites, declined triexponentially; plasma half-lives (t1/2 lambda 1, 0.2 to 0.4 hr; t1/2 lambda 2, 1.3 to 1.7 hr; t1/2 lambda 3, 22 to 40 hr) and total body clearance (CLTB 2.8 +/- 0.5 L/m2/hr) were dose independent. Maximum plasma concentrations (Cmax) and area under the plasma concentration time curve (AUC) increased proportionally with dose. Plasma ultrafilterable platinum and carboplatin concentrations at doses of 375 and 450 mg/m2 declined in a biphasic manner. Plasma carboplatin elimination (t1/2 lambda 1, 0.50 hr; t1/2 lambda 2, 2.2 hr) and CLTB (4.4 to 5.6 L/m2/hr) were also independent of dose; AUC and Cmax increased proportionally to dose. Plasma free platinum was essentially all carboplatin for 8 or 12 hours after administration. Carboplatin did not bind to plasma protein in vitro but did degrade (t1/2-26 hours) to yield a reactive intermediate that bound rapidly and irreversibly to protein. The long terminal elimination half-life of plasma platinum was associated with irreversible binding of a platinum metabonate to plasma protein. The urinary excretion of platinum (0 to 24 hours) accounted for 58 to 72% of doses in 12 to 24 hours. The remainder of the dose is slowly excreted. The pharmacokinetics, in vivo stability, protein binding, and elimination of carboplatin are distinct from the first-generation analog cisplatin.

A modified pharmacokinetic model for platinum disposition in ovarian cancer patients receiving cisplatin

We have fitted a first-order multicompartment pharmacokinetic model to plasma platinum concentrations measured in nine ovarian cancer patients who received intravenous infusions of cisplatin for 6 h. The time-course of ultrafilterable plasma platinum was similar in all patients studied, and was fitted by a single compartment within the limits of experimental detection. However, the time-course of protein-bound platinum showed marked differences between patients, the differences being explained by distribution to two peripheral compartments. The wide inter-patient variation observed in protein-bound plasma platinum concentrations supports the view that pharmacokinetic modelling should be carried out separately for each patient, since averaging plasma concentrations would have obscured some individual pharmacokinetic characteristics.

Biliary excretion of platinum in a patient treated with cis-dichlorodiammineplatinum (II)

Biliary excretion of platinum was measured in a patient receiving an intravenous infusion of cis-dichlorodiammineplatinum (II). Over a 3-day period, less than 1% of the administered platinum was detected in the bile, and 47% appeared in the urine, indicating that biliary excretion is a minor route of elimination.