The pharmacokinetics of dexrazoxane have been studied in advanced cancer patients with normal renal and hepatic function. The pharmacokinetics of dexrazoxane can be adequately described by a two-compartment open model with first-order elimination. Dexrazoxane has been administered as a 15 minute infusion over a dose range of 60 to 900 mg/m2 with 60 mg/m2 of doxorubicin, and at a fixed dose of 500 mg/m2 with 50 mg/m2 doxorubicin. The disposition kinetics of dexrazoxane are dose-independent, as shown by linear relationship between the area under plasma concentration-time curves and administered doses ranging from 60 to 900 mg/m2. The mean peak plasma concentration of dexrazoxane was 36.5 mcg/mL at 15 minute after intravenous administration of 500 mg/m2 dose of dexrazoxane for injection over 15 to 30 minutes prior to the 50 mg/m2 doxorubicin dose.
The important pharmacokinetic parameters of dexrazoxane are summarized in Table 2:
Table 2: Summary of Mean (%CVa) Dexrazoxane Pharmacokinetic Parameters at a Dosage Ratio of 10:1 of Dexrazoxane: Doxorubicina Coefficient of variation b Steady-state volume of distribution
|
Dose Doxorubicin (mg/m2)
| Dose Dexrazoxane (mg/m2)
| Number of Subjects
| Elimination Half-Life (h)
| Plasma Clearance (L/h/m2)
| Renal Clearance (L/h/m2)
| bVolume of Distribution (L/m2)
|
50
| 500
| 10
| 2.5 (16)
| 7.88 (18)
| 3.35 (36)
| 22.4 (22)
|
60
| 600
| 5
| 2.1 (29)
| 6.25 (31)
| ---
| 22.0 (55)
|
Distribution: Following a rapid distributive phase (0.2 to 0.3 hours), dexrazoxane reaches post-distributive equilibrium within 2 to 4 hours. The estimated mean steady-state volume of distribution of dexrazoxane is 22.4 L/m2 after 500 mg/m2 of dexrazoxane dose followed by 50 mg/m2 of doxorubicin, suggesting distribution throughout total body water (25 L/m2).
In vitro studies have shown that dexrazoxane is not bound to plasma proteins.
Metabolism: Qualitative metabolism studies with dexrazoxane have confirmed the presence of unchanged drug, a diacid-diamide cleavage product, and two monoacid-monoamide ring products in the urine of animals and man. The metabolite levels were not measured in the pharmacokinetic studies.
Excretion: Urinary excretion plays an important role in the elimination of dexrazoxane. Forty-two percent of a 500 mg/m2 dose of dexrazoxane was excreted in the urine. Renal clearance averages 3.35 L/h/m2 after the 500 mg/m2 dexrazoxane for injection dose followed by 50 mg/m2 of doxorubicin.
Specific Populations:
Pediatric: Pharmacokinetics following dexrazoxane administration have not been evaluated in pediatric patients.
Effect of Renal Impairment: The pharmacokinetics of dexrazoxane were assessed following a single 15 minute IV infusion of 150 mg/m2 of dexrazoxane. Dexrazoxane clearance was reduced in subjects with renal dysfunction. Compared with controls, the mean AUC0-inf value was 2-fold greater in subjects with moderate (CLCR 30 to 50 mL/min) to severe (CLCR < 30 mL/min) renal dysfunction. Modeling demonstrated that equivalent exposure (AUC-inf) could be achieved if dosing were reduced by 50% in subjects with creatinine clearance values < 40 mL/min compared with control subjects (CLCR > 80 mL/min) [see Use in Specific Populations (8.7) and Dosage and Administration (2.2)].
Effect of Hepatic Impairment: The following dexrazoxane administration have not been evaluated in patients with hepatic impairment. The dexrazoxane dose is dependent upon the dose of doxorubicin [see Dosage and Administration (2.2)].
Drug Interactions: There was no significant change in the pharmacokinetics of doxorubicin (50 mg/m2) and its predominant metabolite, doxorubicinol, in the presence of dexrazoxane (500 mg/m2) in a crossover study in cancer patients.