Pharmacokinetics of dexrazoxane in subjects with impaired kidney function.

Dexrazoxane is approved as a cardioprotective agent for use in female patients with breast cancer who are receiving doxorubicin. The effect of renal insufficiency on elimination is not known. The pharmacokinetics of dexrazoxane 150 mg/m(2), given as a 15-minute constant-rate intravenous infusion, were assessed in 24 men and women with varying degrees of renal function in a single-dose, open-label, parallel-group study. Blood and urine samples were measured by a validated liquid chromatography/mass spectrometry assay. Dexrazoxane pharmacokinetic parameters were derived by standard noncompartmental methods. The effect of kidney function and effect of body surface area on the pharmacokinetics of dexrazoxane were analyzed using linear and nonlinear regression in the SPSS statistical program. Dexrazoxane clearance is decreased in subjects with kidney dysfunction. Compared with normal subjects (creatinine clearance [CL(CR)] >80 mL/min), mean area under the concentration curve from time 0 to infinity (AUC(0-inf)) was 2-fold greater in subjects with moderate (CL(CR) 30-50 mL/min) to severe (CL(CR) <30 mL/min) renal dysfunction. Modeling demonstrated that equivalent exposure (AUC(0-inf)) could be achieved if dosing were reduced by 50% in subjects with CL(CR) less than 40 mL/min compared with control subjects (CL(CR) >80 mL/min). Modeling study results suggested that equivalent exposure could be achieved if dosing was halved in subjects with CL(CR) less than 40 mL/min compared with controls.

Metabolism of the one-ring open metabolites of the cardioprotective drug dexrazoxane to its active metal-chelating form in the rat.

Dexrazoxane (ICRF-187) is clinically used as a doxorubicin cardioprotective agent and may act by preventing iron-based oxygen free radical damage through the iron-chelating ability of its fully hydrolyzed metabolite ADR-925 (N,N'-[(1S)-1-methyl-1,2-ethanediyl]-bis[(N-(2-amino-2-oxoethyl)]glycine). Dexrazoxane undergoes initial metabolism to its two one-ring open intermediates and is then further metabolized to its active metal ion-binding form ADR-925. The metabolism of these intermediates to the ring-opened metal-chelating product ADR-925 has been determined in a rat model to identify the mechanism by which dexrazoxane is activated. The plasma concentrations of both intermediates rapidly decreased after their i.v. administration to rats. A maximum concentration of ADR-925 was detected 2 min after i.v. bolus administration, indicating that these intermediates were both rapidly metabolized in vivo to ADR-925. The kinetics of the initial appearance of ADR-925 was consistent with formation rate-limited metabolism of the intermediates. After administration of dexrazoxane or its two intermediates, ADR-925 was detected in significant levels in both heart and liver tissue but was undetectable in brain tissue. The rapid rate of metabolism of the intermediates was consistent with their hydrolysis by tissue dihydroorotase. The rapid appearance of ADR-925 in plasma may make ADR-925 available to be taken up by heart tissue and bind free iron. These studies showed that the two one-ring open metabolites of dexrazoxane were rapidly metabolized in the rat to ADR-925, and thus, these results provide a mechanism by which dexrazoxane is activated to its active metal-binding form.

Metabolism of the cardioprotective drug dexrazoxane and one of its metabolites by isolated rat myocytes, hepatocytes, and blood.

The metabolism of the antioxidant cardioprotective agent dexrazoxane (ICRF-187) and one of its one-ring open metabolites to its active metal ion binding form N,N'-[(1S)-1-methyl-1,2-ethanediyl-]bis[(N-(2-amino-2-oxoethyl)]glycine (ADR-925) has been investigated in neonatal rat myocyte and adult rat hepatocyte suspensions, and in human and rat blood and plasma with a view to characterizing their hydrolysis-activation. Dexrazoxane is clinically used to reduce the iron-based oxygen free radical-mediated cardiotoxicity of the anticancer drug doxorubicin. Dexrazoxane may act through its hydrolysis product ADR-925 by removing iron from the iron-doxorubicin complex, or binding free iron, thus preventing oxygen radical formation. Our results indicate that dexrazoxane underwent partial uptake and/or hydrolysis by myocytes. A one-ring open metabolite of dexrazoxane underwent nearly complete dihydroorotase-catalyzed metabolism in a myocyte suspension. Hepatocytes that contain both dihydropyrimidinase and dihydroorotase completely hydrolyzed dexrazoxane to ADR-925 and released it into the extracellular medium. Thus, in hepatocytes, the two liver enzymes acted in concert, and sequentially, on dexrazoxane, first to produce the two ring-opened metabolites, and then to produce the metabolite ADR-925. We also showed that the hydrolysis of one of these metabolites was promoted by Ca2+ and Mg2+ in plasma, and thus, further metabolism of these intermediates likely occurs in the plasma after they are released from the liver and kidney. In conclusion, these studies provide a nearly complete description of the metabolism of dexrazoxane by myocytes and hepatocytes to its presumably active form, ADR-925.

Pharmacokinetics of etoposide in cancer patients treated with high-dose etoposide and with dexrazoxane (ICRF-187) as a rescue agent.

PURPOSE: The pharmacokinetics of etoposide were studied in cancer patients with brain metastases treated with high-dose etoposide in order to determine if the pharmacokinetics were altered by the use of dexrazoxane as a rescue agent to reduce the extracerebral toxicity of etoposide. METHODS: Etoposide plasma levels were determined by HPLC. RESULTS: The etoposide pharmacokinetics described by a monophasic first-order elimination model were found to be similar to other reported data in other settings and at similar doses. CONCLUSIONS: The pharmacokinetics of etoposide were unaffected by dexrazoxane rescue.

Metabolism of dexrazoxane (ICRF-187) used as a rescue agent in cancer patients treated with high-dose etoposide.

PURPOSE: The study was undertaken to determine the metabolism of dexrazoxane (ICRF-187) to its one-ring open hydrolysis products and its two-rings opened metal-chelating product ADR-925 in cancer patients with brain metastases treated with high-dose etoposide. In this phase I/II trial dexrazoxane was used as a rescue agent to reduce the extracerebral toxicity of etoposide. METHODS: Dexrazoxane and its one-ring open hydrolysis products were determined by HPLC and ADR-925 was determined by a fluorescence flow injection assay. RESULTS: The two one-ring open hydrolysis intermediates of dexrazoxane appeared in the plasma at low levels upon completion of dexrazoxane infusion and then rapidly decreased with half-lives of 0.6 and 2.5 h. A plasma concentration of 10 micro M ADR-925 was also detected at the completion of the dexrazoxane i.v. infusion period, indicating that dexrazoxane was rapidly metabolized in vivo. A plateau level of 30 micro M ADR-925 was maintained for 4 h and then slowly decreased. The pharmacokinetics of dexrazoxane were found to be similar to other reported data in other settings and at lower doses. CONCLUSIONS: The rapid appearance of ADR-925 in plasma may make ADR-925 available to be taken up by heart tissue and bind free iron. These results suggest that the dexrazoxane intermediates are enzymatically metabolized to ADR-925 and provide a pharmacodynamic basis for the antioxidant cardioprotective activity of dexrazoxane.

Comparative open, randomized, cross-over bioequivalence study of two intravenous dexrazoxane formulations (Cardioxane and ICRF-187) in patients with advanced breast cancer, treated with 5-fluorouracil-doxorubicin-cyclophosphamide (FDC).

The purpose of this study was to compare the pharmacokinetic disposition of two intravenous dexrazoxane formulations, and their effects on doxorubicin's kinetics and metabolism. Plasma concentration versus time curves and pharmacokinetic parameters of dexrazoxane given as Cardioxane (dexrazoxane hydrochloride salt) and ICRF-187 reference formulation (dexrazoxane base) were determined and compared. Both formulations were administered as a single intravenous infusion prior to 5-fluorouracil-doxorubicin-cyclophosphamide administration. In addition, the pharmacokinetics of doxorubicin and its metabolites were studied after dexrazoxane administration. A total of 15 patients with advanced breast cancer participated in this open, randomized, cross-over study and 12 patients were evaluable. Plasma concentrations of dexrazoxane, doxorubicin and doxorubicin metabolites were determined by high-performance liquid chromatography in samples obtained in the 72 h after drug administration. No statistically significant differences were found in the tested kinetic parameters when the two products were compared by analysis of variance (ANOVA) on log-transformed data. Cardioxane fulfilled the bioequivalence criteria when compared with ICRF-187 reference formulation for all of the investigated parameters (AUC, t1/2beta, Vdss, Cl(tot), Cl(ren)). The parametric 90% confidence intervals were contained within the bioequivalence interval (0.8-1.25). Pharmacokinetic parameters and metabolism of doxorubicin were not different after the administration of either Cardioxane or ICRF-187 formulation. From the results of this study it can be concluded that the two formulations can be considered bioequivalent with regard to extent of absorption (AUC and Vdss) and elimination (t1/2beta, Cl(tot) and Cl(ren)).

Stereoselective metabolism of dexrazoxane (ICRF-187) and levrazoxane (ICRF-186).

A chiral HPLC method has been developed to separate razoxane (ICRF-159) in blood plasma into its enantiomers dexrazoxane (ICRF-187) and levrazoxane (ICRF-186). Dexrazoxane is clinically used as a doxorubicin cardioprotective agent and little is known of its in vivo metabolism. After intravenous administration of 20 mg/kg of razoxane to rats, the razoxane was eliminated from the plasma with a half-time of approximately 20 min. The levrazoxane:dexrazoxane ratio continuously increased with time to a value of 1.5 at 150 min, indicating that dexrazoxane is metabolized faster than levrazoxane. These results, confirmed with studies on liver supernatants, are consistent with the hypothesis that dihydropyrimidine amidohydrolase in the liver and kidney is responsible for the preferential metabolism of dexrazoxane in the rat compared to levrazoxane. It is possible that on a dose-per-dose basis marginally higher therapeutic levels of levrazoxane might be achieved in the heart tissue for a longer time compared to dexrazoxane due to dihydropyrimidine amidohydrolase-based metabolism in the liver and kidney. However, given the relatively small difference in elimination of the two enantiomers, it would be difficult to predict from this study whether or not dexrazoxane or levrazoxane might be more efficacious in reducing cardiotoxicity.

Relative plasma levels of the cardioprotective drug dexrazoxane and its two active ring-opened metabolites in the rat.

A postcolumn derivatization reversed-phase high-pressure liquid chromatography method has been developed to detect and separate the one-ring open intermediates of dexrazoxane (ICRF-187) in blood plasma. Dexrazoxane is clinically used as a doxorubicin cardioprotective agent and may act by preventing iron-based oxygen-free radical damage through the iron-chelating ability of its one-ring open intermediates and its fully rings opened hydrolysis product ADR-925. Little is known of the in vivo metabolism of dexrazoxane to its one-ring open intermediates, which may be two of the active forms of dexrazoxane. The one-ring open intermediates were detected within 5 min of i.v. administration of dexrazoxane to rats, suggesting that dexrazoxane is rapidly metabolized in vivo. The plasma concentrations of the one-ring open intermediates varied from 4 to 9% and 6 to 24% of the dexrazoxane concentrations at 5 and 120 min, respectively. The relatively small changes in the levels of the one-ring open intermediates with time suggest that a dynamic steady state is occurring. The ratio of the concentrations of the two one-ring open intermediates was similar to that previously seen for the in vitro dihydropyrimidine amidohydrolase-catalyzed hydrolysis of dexrazoxane. These results are consistent with the hypothesis that dihydropyrimidine amidohydrolase in the liver and kidney is responsible for the metabolism of dexrazoxane in the rat.

Plasmodium falciparum and Plasmodium yoelii: effect of the iron chelation prodrug dexrazoxane on in vitro cultures.

To determine if an iron-chelating prodrug that must undergo intracellular hydrolysis to bind iron has antimalarial activity, we examined the action of dexrazoxane on Plasmodium falciparum cultured in human erythrocytes and P. yoelii cultured in mouse hepatocytes. Dexrazoxane was recently approved to protect humans from doxorubucin-induced cardiotoxicity. Using the fluorescent marker calcein, we confirmed that the iron-chelating properties of dexrazoxane are directly related to its ability to undergo hydrolysis. As a single agent, dexrazoxane inhibited synchronized cultures of P. falciparum in human erythrocytes only at suprapharmacologic concentrations (> 200 microM). In combination with desferrioxamine B, dexrazoxane in pharmacologic concentrations (100-200 microM) moderately potentiated inhibition by approximately 20%. In contrast, pharmacologic concentrations of dexrazoxane (50-200 microM) as a single agent inhibited the progression of P. yoelli from sporozoites to schizonts in cultured mouse hepatocytes by 45 to 69% (P < 0.001). These results are consistent with the presence of a dexrazoxane-hydrolyzing enzyme in hepatocytes but not in erythrocytes or malaria parasites. Furthermore, these findings suggest that dexrazoxane must be hydrolyzed to an iron-chelating intermediate before it can inhibit the malaria parasite, and they raise the possibility that the iron chelator prodrug concept might be exploited to synthesize new antimalarial agents.

Dose-independent pharmacokinetics of the cardioprotective agent dexrazoxane in dogs.

A randomized, four-way cross-over design was used to assess the disposition of the cardioprotective agent, dexrazoxane, in four male beagle dogs following single I.V. administration of 10, 25, 50, and 100 mg kg-1 doses. Parent drug was quantified in plasma and urine with a validated high-pressure liquid chromatographic-electrochemical assay. A two-compartment open model adequately described the dexrazoxane plasma concentration versus time data. The terminal half-life ranged between 1.1 and 1.3 h and the apparent steady-state distribution volume was 0.67 L kg-1. The systemic clearance (CL) ranged from 10.3 to 11.5 mL min-1 kg-1, while estimates of renal clearance approximated the glomerular filtration rate (GFR approximately 3.2-4.9 mL min-1 kg-1). Over the dose range evaluated, CL was dose independent (ANOVA, p = 0.33), while concentration at the end of infusion (Cend) and the area under the concentration versus time curve (AUC) were directly proportional to the dose (r > 0.999). The blood cell to plasma partitioning ratio was approximately 0.517 and drug was essentially unbound to plasma proteins (fu approximately 0.95). Dexrazoxane appeared to be subject to low organ extraction, since the hepatic and renal drug extraction ratios were on the order of 0.228 +/- 0.054 and 0.184 +/- 0.024, respectively. These results suggest a relatively small drug distribution space (approximately equal to total-body water) and low tissue and plasma protein binding. In light of the low plasma protein binding and extraction ratio exhibited by dexrazoxane, metabolic capacity and renal function would appear to be the predominant variables affecting the CL of this drug. The constancy of the half-life, CL, and VSS with increasing dose indicates dose-independent disposition for dexrazoxane. Thus a linear increase in the systemic exposure can be predicted over this dose range.

A sensitive and specific procedure for quantitation of ADR-529 in biological fluids by high-performance liquid chromatography (HPLC) with column switching and amperometric detection.

An HPLC method using electrochemical detection (ED) has been validated for the determination of ADR-529 in plasma and urine using ICRF-192 as an internal standard (IS). Prior to storage and quantitation, both plasma and urine samples require acid stabilization. Acidified plasma samples were prepared for HPLC using a two column solid-phase extraction (SPE). An aliquot of buffered plasma (i.e., pH 6-7) was first deproteinated and desalted on a C-18 SPE column. The analytes were then eluted onto a C-8 SPE column where retention and selective cleanup were achieved in the cation-exchange mode via silanol interactions. Acidified urine samples were diluted in acetonitrile prior to injection. The HPLC system for plasma and urine samples employed two narrow-bore silica columns used in the weak cation-exchange mode and separated by a switching valve. To prohibit late-eluting peaks from passivating the glassy carbon working electrode, a heart-cut containing ADR-529 and the IS was vented from the first silica column to the second using an automated switching valve. Amperometric detection at an oxidation potential of +1050 mV vs a Ag/AgNO3 reference electrode was used. Linearity was validated between 5 and 500 ng/ml in plasma and between 2 and 100 micrograms/ml in urine. Imprecision and percentage bias were typically less than 10% for both plasma and urine controls throughout their respective dynamic ranges. The absolute recoveries for ADR-529 and the IS from plasma were greater than 95%. This method is being successfully applied to the pharmacokinetic/dynamic evaluation of ADR-529 in animals and humans.