Effect of phenytoin on the pharmacokinetics of doxorubicin and doxorubicinol in the rabbit

Summary Doxorubicin is metabolized extensively to doxorubicinol by the ubiquitous aldoketoreductase enzymes. The extent of conversion to this alcohol metabolite is important since doxorubicinol may be the major contributor to cardiotoxicity. Aldoketoreductases are inhibited in vitro by phenytoin. The present study was conducted to examine the effect of phenytoin on doxorubicin pharmacokinetics. Doxorubicin single-dose pharmacokinetic studies were performed in 10 New Zealand White rabbits after pretreatment with phenytoin or phenytoin vehicle (control) infusions in crossover fashion with 4–6 weeks between studies. Infusions were commenced 16 h before and during the course of the doxorubicin pharmacokinetic studies. Phenytoin infusion was guided by plasma phenytoin estimation to maintain total plasma concentrations between 20 and 30 g/ml. Following doxorubicin 5 mg/kg by i.v. bolus, blood samples were obtained at intervals over 32 h. Plasma doxorubicin and doxorubicinol concentrations were measured by HPLC. The mean plasma phenytoin concentrations ranged from 17.4 to 33.9 g/ml. Phenytoin infusion did not alter doxorubicin pharmacokinetics. The elimination half-life and volume of distribution were almost identical to control. Clearance of doxorubicin during phenytoin administration (60.9±5.8 ml/min per kg, mean±SE) was similar to that during vehicle infusion (67.5±5.4 ml/min per kg). Phenytoin administration was associated with a significant decrease in doxorubicinol elimination half-life from 41.0±4.8 to 25.6±2.8 h. The area under the plasma concentration/time curve (AUC) for doxorubicinol decreased significantly from 666.8±100.4 to 491.5±65.7 n.h.ml^-1. These data suggest that phenytoin at clinically relevant concentrations does not alter the conversion of doxorubicin to doxorubicinol in the rabbit. The reduction in the AUC for doxorubicinol caused by phenytoin appears to be due to an increased rate of doxorubicinol elimination. Phenytoin or similar agents may have the effect of modifying doxorubicinol plasma concentrations by induction of doxorubicinol metabolism rather than by inhibition of aldoketoreductase enzymes.     

Doxorubicin and doxorubicinol pharmacokinetics and tissue concentrations following bolus injection and continuous infusion of doxorubicin in the rabbit

Cumulative dose-related, chronic cardiotoxicity is a serious clinical complication of anthracycline therapy. Clinical and animal studies have demonstrated that continuous infusion, compared to bolus injection of doxorubicin, decreases the risk of cardiotoxicity. Continuous infusion of doxorubicin may result in decreased cardiac tissue concentrations of anthracyclines, including the primary metabolite doxorubicinol, which may also be an important contributor to cardiotoxicity. In this study, doxorubicin and doxorubicinol plasma pharmacokinetics and tissue concentrations were compared in New Zealand white rabbits following intravenous administration of doxorubicin (5 mg·kg^–1) by bolus and continuous infusion. Blood samples were obtained over a 72-h period after doxorubicin administration to determine plasma doxorubicin and doxorubicinol concentrations. Rabbits were killed 7 days after the completion of doxorubicin administration and tissue concentrations of doxorubicin and doxorubicinol in heart, kidney, liver, and skeletal muscle were measured. In further experiments, rabbits were killed 1 h after bolus injection of doxorubicin and at the completion of a 24-h doxorubicin infusion (anticipated times of maximum heart anthracycline concentrations) to compare cardiac concentrations of doxorubicin and doxorubicinol following both methods of administration. Peak plasma concentrations of doxorubicin (1739±265 vs 100±10 ng·ml^–1) and doxorubicinol (78±3 vs 16±3 ng·ml^–1) were significantly higher following bolus than infusion dosing. In addition, elimination half-life of doxorubicinol was increased following infusion. However, other plasma pharmacokinetic parameters for doxorubicin and doxorubicinol, including AUC, were similar following both methods of doxorubicin administration. Peak left ventricular tissue concentrations of doxorubicin (16.92±0.9 vs 3.59±0.72 g·g^–1 tissue;P<0.001) and doxorubicinol (0.24±0.02 vs 0.09±0.01 g·g^–1 tissue;P<0.01) following bolus injection of doxorubicin were significantly higher than those following infusion administration. Tissue concentrations of parent drug and metabolite in bolus and infusion groups were similar 7 days after dosing. The results suggest that cardioprotection following doxorubicin infusion may be related to attenuation of the peak plasma or cardiac concentrations of doxorubicin and/or doxorubicinol.     

Interaction of dexrazoxane with red blood cells and hemoglobin alters pharmacokinetics of doxorubicin

Purpose: The mechanism of the cardioprotective action of dexrazoxane against doxorubicin cardiotoxicity is not fully understood. It has been suggested that its hydrolysis product, ICRF-198, chelates and removes free iron and iron associated with doxorubicin-iron complex and, therefore, prevents the formation of free radical, lipid peroxidation and cardiotoxicity. Dexrazoxane is also known to inhibit topoisomerase II, to prevent the inactivation of cytochrome c oxidase by Fe³⁺-doxorubicin and to increase the levels of transferrin receptor (trf-rec) mRNA and cellular iron uptake. This sequestration of iron and its effect on cellular iron homeostasis may also contribute to its protective effect against doxorubicin cardiotoxicity. The present project was designed to investigate the interaction of dexrazoxane with hemoglobin and red blood cells and the subsequent effect on the pharmacokinetics and toxicodynamics of doxorubicin. Methods: In an in vitro investigation the binding of doxorubicin (0.5–25 μg/ml) to red blood cells, erythrocyte ghosts and hemoglobin in the presence of dexrazoxane was evaluated. In an in vivo study female Sprague Dawley rats were pretreated with 100 mg/kg of dexrazoxane by intravenous injection 1 h before the injection of ¹⁴C-doxorubicin (specific activity 0.4 μCi/mg, 10 mg/kg). The time-course of doxorubicin associated with blood cells and plasma was evaluated with simultaneous characterization of doxorubicin and its metabolites in the bile and urine. The serum concentration of endothelin was measured as a biomarker of cardiotoxicity in separate groups of animals. Results: The in vitro data indicated that dexrazoxane inhibited the binding of DOX to red blood cells in a concentration-dependent manner. At 1 μg/ml it reduced the binding of doxorubicin to red blood cells by about 30% and at 100 μg/ml by about 60%. It had no effect on the association of doxorubicin with erythrocyte ghosts. The investigation of binding of doxorubicin to hemoglobin revealed the existence of two distinct binding sites and dexrazoxane reduced the association constant of doxorubicin with the low-affinity and high-capacity class of binding sites significantly. The pharmacokinetic analysis showed that pretreatment with dexrazoxane (100 mg/kg) reduced the area under plasma concentration-time curve of doxorubicin, its mean residence time and plasma clearance significantly. Similar reductions were also shown with the pharmacokinetic analysis of doxorubicin associated with blood cells. The biliary and urinary elimination of unchanged doxorubicin increased significantly. The pretreatment reduced the serum concentration of endothelin from about 20 ng/ml to about 12 ng/ml. The per cent of this reduction was proportional to the reduction in the AUC of blood cells. Conclusion: The cardioprotective effect of dexrazoxane is due, in part, to its interaction with hemoglobin and red blood cells and this interaction modifies the pharmacokinetics of DOX. Received: 29 July 1999 / Accepted: 11 February 2000     

Effect of the paclitaxel vehicle, Cremophor EL, on the pharmacokinetics of doxorubicin and doxorubicinol in mice.

The effect of the paclitaxel vehicle Cremophor on the pharmacokinetics of doxorubicin and doxorubicinol was studied in two groups of mice given intravenously either 2.5 ml kg-1 Cremophor or saline followed 5 min later by 10 mg kg-1 doxorubicin. In each group three mice were sacrificed at ten time points and doxorubicin and doxorubicinol were measured in plasma by high-performance liquid chromatography (HPLC). With Cremophor present, doxorubicin AUC increased from 1420+/-440 to 2770+/-660 ng h ml(-1) (P<0.05) and doxorubicinol AUC increased from 130+/-76 to 320+/-88 ng h ml(-1) (p<0.05). Neither the terminal elimination half-lives nor the doxorubicinol-doxorubicin AUC ratio changed in the presence of Cremophor, suggesting a lack of a direct effect on drug metabolism. The possibility exists the Cremophor may change the pharmacokinetics of both paclitaxel and other drugs given concurrently.     

Effect of a low-protein diet on doxorubicin pharmacokinetics in the rabbit

Summary Malnutrition involving protein deficiency, which commonly occurs in cancer patients receiving anthracycline treatment, is considered to be a risk factor for the development of cardiotoxicity. Protein deficiency has been shown to impair the metabolism of drugs such as theophylline and acetaminophen. If protein deficiency also impairs anthracycline metabolism, it could explain at least in part the enchanced anthracycline toxicity associated with malnutrition. We tested this idea by determining the effect of a low- protein, isocaloric diet on doxorubicin pharmacokinetics in rabbits. The animals were randomized into two groups for 8–12 weeks. Rabbits in group 1 received a low-protein (5%), isocaloric diet, whereas those in group 2 received a normal-protein (15%) diet. Both groups (group 1,n=15; group 2,n=14) were given 5 mg/kg doxorubicin by i.v. bolus. After doxorubicin injection, blood samples were obtained over the next 52 h for the measurement of doxorubicin and doxorubicinol plasma concentrations by high-performance liquid chromatography (HPLC) with fluorometric detection. The low-protein diet significantly decreased doxorubicin clearance (48±3 vs 59±4 ml min^–1 kg^–1;P<0.05), prolonged the terminal climination half-life (28±2 vs 22±2 h;P<0.05), and increased the area under the plasma concentration/time curve extrapolated to infinity (1722±122 vs 1405±71 ng h ml^–1;P<0.05) as compared with the values determined for rabbits fed the standard rabbit chow (15% protein). The volume of distribution for doxorubicin was not altered by the low-protein diet. In addition, in rabbits fed the the low-portein diet, the terminal elimination half-life of the alcohol metabolite, doxorubicinol was prolonged (52±5 vs 40±2 h;P<0.05). Thus, a low-protein diet causes a reduction in the ability of rabbits to eliminate doxorubicin and possibly its alcohol metabolite doxorubicinol. If a similar alteration in anthracycline pharmacokinetics occurs in malnourished cancer patients, this phenomenon may contribute to their increased risk of developing cardiotoxicity associated with anthracycline therapy.Supported by the Department of Veterans Affairs and the American Heart Foundation     

Effects of verapamil on the pharmacokinetics of daunomycin in the rat

Summary We compared the pharmacokinetics of daunomycin in two groups of rats: one group was treated with daunomycin (7.5 mg/kg) alone and the other group was treated with daunomycin (7.5 mg/kg) plus the calcium antagonist verapamil (2x50 mg/kg i. p.). Due to a much slower decrease in plasma concentrations the daunomycin AUC_O was dramatically increased (8 times) in the animals treated with anthracycline plus verapamil. The daunomycin plasma clearance was found to be decreased about 9 times in the verapamil-treated group. Verapamil had a differential effect on the tissue distribution of daunomycin. Of the organs examined the heart, liver, and lungs showed an increased (about 2–3 times) AUC of daunomycin. In the kidneys and spleen the AUCs of daunomycin were about equal in both groups of rats, while in the femoral bone marrow the daunomycin AUC was significantly reduced by the simultaneous administration of verapamil. Our data suggest that an increased risk for anthracycline-induced cardiotoxicity can be anticipated by the combined treatment of anthracycline drugs with calcium antagonists.     

Prevention of chronic anthracycline cardiotoxicity in the adult Fischer 344 rat by dexrazoxane and effects on iron metabolism

Purpose: Anthracyclines, such as doxorubicin and daunorubicin, continue to be widely used in the treatment of cancer, although they share the adverse effect of chronic, cumulative dose-related cardiotoxicity. The only approved treatment in prevention of anthracycline cardiotoxicity is dexrazoxane, a putative iron chelator. Previous in vitro studies have shown that disorders of iron metabolism, including altered IRP1–IRE binding, may be an important mechanism of anthracycline cardiotoxicity. Methods: This study examined the role of IRP1–IRE binding ex vivo in a chronic model of daunorubicin cardiotoxicity in the Fischer 344 rat and whether dexrazoxane could prevent any daunorubicin-induced changes in IRP1 binding. Young adult (5–6 months) Fischer 344 rats received daunorubicin (2.5 mg/kg iv once per week for 6 weeks) with and without pretreatment with dexrazoxane (50 mg/kg ip). Other groups received saline (controls) or dexrazoxane alone. Rats were killed either 4 h or 2 weeks after the last dose of daunorubicin to assess IRP1–IRE binding. Results: Contractility (dF/dt) of atrial tissue, obtained from rats 2 weeks after the last dose of daunorubicin, was significantly reduced in daunorubicin-treated compared to control rats. Dexrazoxane pretreatment protected against the daunorubicin-induced decrease in atrial dF/dt. However, left ventricular IRP1/IRE binding was not affected by daunorubicin treatment either 4 h or 2 weeks after the last dose of daunorubicin. Conclusions: IRP1 binding may not be altered in the rat model of chronic anthracycline cardiotoxicity.The authors state there are no conflicts of interest regarding the work in this paper.     

Influence of the cardioprotective agent dexrazoxane on doxorubicin pharmacokinetics in the dog

Summary The influence of dexrazoxane on doxorubicin pharmacokinetics was investigated in four dogs using the two treatment sequences of saline/doxorubicin or dexrazoxane/doxorubicin. Intravenous doses of 1.5 mg/kg doxorubicin and 30 mg/kg (the 20-fold multiple) dexrazoxane were given separately, with doxorubicin being injected within 1 min of the dexrazoxane dose. Both doxorubicin and its 13-dihydro metabolite doxorubicinol were quantified in plasma and urine using a validated high-performance liquid chromatographic (HPLC) fluorescence assay. The doxorubicin plasma concentration versus time data were adequately fit by a three-compartment model. The mean half-lives calculated for the fast and slow distributive and terminal elimination phases in the saline/doxorubicin group were 3.0±0.5 and 32.2±12.8 min and 30.0±4.0 h, respectively. The model-predicted plasma concentrations were virtually identical for the saline and dexrazoxane treatment groups. Analysis of variance of the area under the plasma concentration-time curve (AUC_0–), terminal elimination rate (_Z), systemic clearance (CL _s), and renal clearance (CL _r) for the parent drug showed no statistically significant difference (P<0.05) between the two treatments. Furthermore, the doxorubicinol plasma AUC_0– value and the doxorubicinol-to-doxorubicin AUC_0– ratio showed no significant difference, demonstrating that dexrazoxane had no effect on the metabolic capacity for formation of the 13-dihydro metabolite. The total urinary excretion measured as parent drug plus doxorubicinol and the metabolite-to-parent ratio in urine were also unaffected by the presence of dexrazoxane. The myelosuppressive effects of doxorubicin as determined by WBC monitoring revealed no apparent difference between the two treatments. In conclusion, these results show that drug exposure was similar for the two treatment arms. No kinetic interaction with dexrazoxane suggests that its coadministration is unlikely to modify the safety and/or efficacy of doxorubicin.     

The effect of age on the early disposition of doxorubicin

PURPOSE: Clinical studies indicate that anthracycline cardiotoxicity increases with patient age. This may be due to altered pharmacokinetics or pharmacodynamics. A parameter termed 'early clearance' has been shown to decrease with age in patients receiving intravenous doxorubicin. This parameter, as defined, has no immediate relationship to any physiologically based pharmacokinetic parameter. We therefore reevaluated the pharmacokinetic data to better define the relationship between doxorubicin disposition and patient age. METHODS: Four studies provided a total of 56 patients with evaluable pharmacokinetics. The volume of the central compartment, V(c), the distribution clearance, CL(d), and total body clearance, CL, were determined for each patient and regressed against age. A physiologically based pharmacokinetic (PBPK) model for doxorubicin was also used to evaluate the effects of age on doxorubicin disposition. Published blood flows associated with various patient ages were used to simulate plasma and tissue doxorubicin concentrations. The relationship between CL(d) and initial tumor regression was also evaluated. RESULTS: No correlation was found between V(c) and age ( P>0.05). A highly significant correlation was observed between CL(d) and age ( P<0.0005) and there was a mild but significant relationship between CL and age ( P<0.01). Use of the PBPK model with different age-related blood flows yielded virtually identical parameter values to the clinical data analyzed. Furthermore, relative tissue AUCs simulated in old and young patients compared well with those reported for daunorubicin disposition in young and old rats. In addition, a linear relationship was observed between initial tumor regression and CL(d). CONCLUSIONS: Initial concentrations of doxorubicin following intravenous administration are higher in the elderly due to a decrease in CL(d) rather than in V(c). On the basis of simulations with the PBPK model, the reduced CL(d) appears to be related to altered regional blood flows in the elderly, and such changes may be of clinical significance.     

Multicenter randomized phase III study of the cardioprotective effect of dexrazoxane (Cardioxane) in advanced/metastatic breast cancer patients treated with anthracycline-based chemotherapy.

BACKGROUND: Anthracycline-induced cardiotoxicity has led to the adoption of empirical dose limits that may restrict continued use of anthracyclines among patients who might benefit. Dexrazoxane, a cardioprotective agent, has been shown to reduce the risk of anthracycline-associated cardiotoxicity when given from first dose of anthracycline. This study sought to confirm the benefit of dexrazoxane in patients at high risk of cardiotoxicity due to prior anthracycline use. PATIENTS AND METHODS: A total of 164 female breast cancer patients, previously treated with anthracyclines, received anthracycline-based chemotherapy either with (n = 85) or without (n = 79) dexrazoxane for a maximum of six cycles. RESULTS: Compared with those receiving anthracycline alone, patients treated with dexrazoxane experienced significantly fewer cardiac events (39% versus 13%, P < 0.001) and a lower and less severe incidence of congestive heart failure (11% versus 1%, P < 0.05). Tumor response rate was unaffected by dexrazoxane therapy. The frequency of adverse events was similar between groups and there were no significant between-group differences in the number of dose modifications/interruptions. CONCLUSION: Dexrazoxane significantly reduced the occurrence and severity of anthracycline-induced cardiotoxicity in patients at increased risk of cardiac dysfunction due to previous anthracycline treatment without compromising the antitumor efficacy of the chemotherapeutic regimen.     

Plasma pharmacokinetics and tissue distribution of 17-(allylamino)-17-demethoxygeldanamycin (NSC 330507) in CD2F1 mice1

PURPOSE: 17-(Allylamino)-17-demethoxygeldanamycin (17AAG) is a benzoquinone ansamycin compound agent that has entered clinical trials. Studies were performed in mice to: (1) define the plasma pharmacokinetics, tissue distribution, and urinary excretion of 17AAG after i.v. delivery; (2) to define the bioavailability of 17AAG after i.p. and oral delivery; and (3) to characterize the concentrations of 17AAG metabolites in plasma and tissue. MATERIALS AND METHODS: All studies were performed in female CD2F1 mice. Preliminary toxicity studies used 17AAG i.v. bolus doses of 20, 40 and 60 mg/kg. Pharmacokinetic studies used i.v. 17AAG doses of 60, 40, and 26.67 mg/kg and i.p. and oral doses of 40 mg/kg. The plasma concentration versus time data were analyzed by compartmental and noncompartmental methods. The concentrations of 17AAG were also determined in brain, heart, lung, liver, kidney, spleen, skeletal muscle, and fat. Urinary drug excretion was calculated until 24 h after treatment. RESULTS: A 60 mg/kg dose of 17AAG, in its initial, microdispersed formulation, caused no changes in appearance, appetite, waste elimination, or survival of treated animals as compared to vehicle-treated controls. Bolus i.v. delivery of 60 mg/kg microdispersed 17AAG produced "peak" plasma 17AAG concentrations between 5.8 and 19.3 micrograms/ml in mice killed 5 min after injection. Sequential reduction of the 17AAG dose to 40 and 26.67 mg/kg resulted in "peak" plasma 17AAG concentrations between 8.9 and 19.0 micrograms/ml, and 4.8 and 6.1 micrograms/ml, respectively. Noncompartmental analysis of the plasma 17AAG concentration versus time data showed an increase in AUC from 402 to 625 and 1738 micrograms/ml.min when the 17AAG dose increased from 26.67 to 40 and 60 mg/kg, respectively. Across the range of doses studied, 17AAG total body clearance varied from 34 to 66 ml/min per kg. Compartmental modeling of the plasma 17AAG concentration versus time data showed that the data were fitted best by a two-compartment, open, linear model. In each study, substantial concentrations of a material, subsequently identified as 17-(amino)-17-demethoxygeldanamycin (17AG), were measured in plasma. A subsequent, lyophilized formulation of 17AAG proved excessively toxic when delivered i.v. at 60 mg/kg. A repeat i.v. study using a 40 mg/kg dose of this new formulation produced peak plasma 17AAG concentrations of 20.2-38.4 micrograms/ml, and a 17AAG AUC of 912 micrograms/ml.min, which was approximately 50% greater than the AUC produced by a 40 mg/kg dose of microdispersed 17AAG. The bioavailabilities of 17AAG after i.p. and oral delivery were 99% and 24%, respectively. Minimal amounts of 17AAG and 17AG were detected in the urine. After i.v. bolus delivery to mice, 17AAG distributed rapidly to all tissues, except the brain. Substantial concentrations of 17AG were measured in each tissue. CONCLUSIONS: 17AAG has excellent bioavailability when given i.p. but only modest bioavailability when given orally and is metabolized to 17AG and other metabolites when given i.v., i.p., or orally. 17AAG is widely distributed to tissues. These pharmacokinetic data generated have proven relevant to the design of recently initiated clinical trials of 17AAG and could be useful in their interpretation.     

Increased accumulation of doxorubicin and doxorubicinol in cardiac tissue of mice lacking mdr1a P-glycoprotein.

To gain more insight into the pharmacological role of endogenous P-glycoprotein in the metabolism of the widely used substrate drug doxorubicin, we have studied the plasma pharmacokinetics, tissue distribution and excretion of this compound in mdr1a(-/-) and wild-type mice. Doxorubicin was administered as an i.v. bolus injection at a dose level of 5 mg kg(-1). Drug and metabolite concentrations were determined in plasma, tissues, urine and faeces by high-performance liquid chromatography. In comparison with wild-type mice, the terminal half-life and the area under the plasma concentration-time curve of doxorubicin in mdr1a(-/-) mice were 1.6- and 1.2-fold higher respectively. The retention of both doxorubicin and its metabolite doxorubicinol in the hearts of mdr1a(-/-) mice was substantially prolonged. In addition, a significantly increased drug accumulation was observed in the brain and the liver of mdr1a(-/-) mice. The relative accumulation in most other tissues was not or only slightly increased. The differences in cumulative faecal and urinary excretion of doxorubicin and metabolites between both types of mice were small. These experiments demonstrate that the absence of mdr1a P-glycoprotein only slightly alters the plasma pharmacokinetics of doxorubicin. Furthermore, the substantially prolonged presence of both doxorubicin and doxorubicinol in cardiac tissue of mdr1a(-/-) mice suggests that a blockade of endogenous P-glycoprotein in patients, for example by a reversal agent, may enhance the risk of cardiotoxicity upon administration of doxorubicin.     

Pharmacokinetics, tissue distribution, and metabolism of 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (NSC 707545) in CD2F1 mice and Fischer 344 rats

PURPOSE: 17-(Dimethylaminoethylamino)-17-demethoxygeldanamycin (17DMAG) is an analogue of the benzoquinone ansamycin compound 17-(allylamino)-17-demethoxygeldanamycin (17AAG), which is currently being evaluated in clinical trials. Studies were performed in mice and rats to: (1) define the plasma pharmacokinetics, tissue distribution, and urinary excretion of 17DMAG after i.v. delivery; (2) define the bioavailability of 17DMAG after i.p. and oral delivery; (3) characterize the biliary excretion of 17DMAG after i.v. delivery to rats; and (4) characterize, if possible, any metabolites of 17DMAG observed in plasma, tissue, urine, or bile. MATERIALS AND METHODS: Studies were performed in female, CD2F1 mice or male Fischer 344 rats. In preliminary toxicity studies and subsequent i.v. pharmacokinetic studies in mice, 17DMAG i.v. bolus doses of 33.3, 50, and 75 mg/kg were used. In bioavailability studies, i.p. and oral 17DMAG doses of 75 mg/kg were used. In preliminary toxicity studies in rats, i.v. bolus doses of 10 and 20 mg/kg were used, and in i.v. pharmacokinetic studies 10 mg/kg was used. Compartmental and noncompartmental analyses were applied to the plasma concentration versus time data. In mice and rats, concentrations of 17DMAG were determined in multiple tissues. Urine was collected from mice and rats treated with each of the i.v. doses of 17DMAG mentioned above, and drug excretion was calculated until 24 h after treatment. Biliary excretion of 17DMAG and metabolites was studied in bile duct-cannulated rats given a 10 mg/kg i.v. bolus dose of 17DMAG. 17DMAG metabolites were identified with LC/MS. RESULTS: A 75 mg/kg dose of 17DMAG caused no changes in appearance, appetite, waste elimination, or survival of treated mice as compared to vehicle-treated controls. Bolus i.v. delivery of 17DMAG at 75 mg/kg produced "peak" plasma 17DMAG concentrations between 18 and 24.2 microg/ml in mice killed at 5 min after injection. Sequential reduction in the 17DMAG dose to 50 and 33.3 mg/kg resulted in "peak" plasma 17DMAG concentrations between 9.4 and 14.4, and 8.4 and 10.5 microg/ml, respectively. Plasma 17DMAG AUC increased from 362 to 674 and 1150 microg/ml x min when the 17DMAG dose increased from 33.3 to 50 and 75 mg/kg, respectively, corresponding to a decrease in 17DMAG CLtb from 92 ml/min per kg to 75 and 65 ml/min per kg. Plasma 17DMAG concentration versus time data were best fit by a two-compartment open linear model. No potential 17DMAG metabolites were observed in plasma. 17DMAG bioavailability was 100% and 50% after i.p. and oral delivery, respectively. In rats, an i.v. bolus dose of 10 mg/kg produced peak plasma 17DMAG concentrations between 0.88 and 1.74 microg/ml. Plasma 17DMAG concentrations had fallen below the lower limit of quantitation by 180 min and were best fit by a one-compartment open linear model. The plasma 17DMAG AUC was 104 microg/ml x min, corresponding to a 17DMAG CLtb of 96 ml/min per kg. 17DMAG distributed rapidly to all mouse and rat tissues except brain and testes. Only mouse liver contained materials consistent with potential metabolites of 17DMAG, but their concentrations were below the limit of quantitation of the HPLC assay used. Within the first 24 h after delivery, urinary excretion of 17DMAG by mice and rats accounted for 10.6-14.8% and 12.5-16%, respectively, of the delivered dose. By 15 min after i.v. delivery of 10 mg/kg of 17DMAG, rat bile contained 11 new materials with absorbance similar to that of 17DMAG. Four of these proposed metabolites had an Mr of 633, indicating addition of an oxygen. Two of these proposed metabolites had an Mr of 603, implying the loss of one methyl group, and one had an Mr of 589, implying the loss of two methyl groups. The remaining four proposed metabolites had an Mr of 566, 571, 629, and 645, respectively. Biliary excretion of 17DMAG and metabolites accounted for 4.7 +/- 1.4% of the delivered dose, with 17DMAG accounting for 50.7 +/- 3.4% of the biliary excretion. CONCLUSIONS: 17DMAG has excellent bioavailability when given i.p. and good bioavailability when given orally. 17DMAG is widely distributed to tissues and is quantitatively metabolized much less than is 17AAG. The pharmacokinetic and metabolite data generated should prove relevant to the design of additional preclinical studies as well as to contemplated clinical trials of 17DMAG and could be useful in their interpretation.     

Paclitaxel and docetaxel enhance the metabolism of doxorubicin to toxic species in human myocardium.

Doxorubicin cardiotoxicity is a multifactorial process in which the alcohol metabolite doxorubicinol mediates the transition from reversible to irreversible damage. We investigated whether the tubulin-active taxane paclitaxel increases conversion of doxorubicin to doxorubicinol, thus explaining the high incidence of congestive heart failure when doxorubicin is used with paclitaxel. Specimens of human myocardium from patients undergoing bypass surgery were processed to obtain cytosolic fractions in which doxorubicin was converted to doxorubicinol by NADPH-dependent aldo/keto or carbonyl reductases. In this model, clinically relevant concentrations of paclitaxel (1-2.5 microM) increased doxorubicinol formation by mechanisms consistent with allosteric modulation of the reductases. Stimulation was observed over a broad range of basal enzymatic activity, and was accompanied by a similar pattern of enhanced formation of doxorubicinol aglycone, a metabolite potentially involved in the reversible phase of cardiotoxicity. The closely related analogue docetaxel had effects similar to paclitaxel, but increased doxorubicinol formation over a narrower range of enzymatic activity. The unrelated tubulin-active alkaloid vinorelbine had no effect. These results demonstrate that taxanes have a unique potential for enhancing doxorubicin metabolism to toxic species in human myocardium. The effects on doxorubicinol formation provide clues to explain the clinical pattern of doxorubicin-paclitaxel cardiotoxicity and also caution against the potential toxicity of combining docetaxel with high cumulative doses of doxorubicin.     

Comparative metabolism and pharmacokinetics of doxorubicin and 4′-epidoxorubicin in plasma,heart and tumor of tumor-bearing mice

Epidoxorubicin, a stereoisomer of doxorubicin, shows comparable antitumor activity but diminished cardiotoxicity compared with the latter. To find a pharmacokinetic basis for the observed difference in cardiotoxicity between the drugs, concentrations of doxorubicin, epidoxorubicin and all known metabolites were measured in the plasma, heart and tumor tissue of BALB/c mice bearing colon-26 tumors. Both drugs were injected at the same dose (10 mg/kg) as an i.v. bolus. Plasma, heart and tumor samples were obtained from two mice sacrificed at regular intervals over 48 h. Plasma and tissue extracts were analyzed by HPLC with fluorescence detection. The parent compounds and the two 7d-aglycones were present in all three compartments, whereas doxorubicinol (Aol) and epidoxorubicinol (Eol) could only be detected in the plasma and heart. Half-lives and AUCs of doxorubicin and its metabolites were higher than the corresponding values for epidoxorubicin and its metabolites in all three compartments.     

Pharmacokinetics of the cardioprotector ADR-529 (ICRF-187) in escalating doses combined with fixed-dose doxorubicin.

BACKGROUND: Although doxorubicin is an anticancer agent with a wide spectrum of activity, therapy with this anthracycline must often be discontinued at a time of benefit to the patient because of the drug's cumulative cardiotoxicity. ICRF-187 (ADR-529, dexrazoxane) is a bisdioxopiperazine compound that protects against cardiac toxicity induced by doxorubicin. PURPOSE: Our objectives in this study were to determine the maximum tolerated dose of ADR-529 (which uses a different vehicle than ICRF-187) when given with a fixed doxorubicin dose and to determine whether ADR-529 alters doxorubicin pharmacokinetics. METHODS: Twenty-five patients were treated with doxorubicin (60 mg/m2) preceded by administration of ADR-529 in escalating dosages (i.e., 60, 300, 600, 750, and 900 mg/m2) to groups of three to nine patients. ADR-529 was administered over a 15-minute period beginning 30 minutes before doxorubicin treatment; the protocol was repeated every 3 weeks. Blood was sampled frequently for drug levels, which were determined by high-pressure liquid chromatography with fluorescence (doxorubicin) and electrochemical detection (ADR-529). RESULTS: Dose-limiting neutropenia occurred in four of six previously treated patients at an ADR-529 dose of 600 mg/m2; the dose ratio of ADR-529 to doxorubicin was 10:1. For three additional patients with better Eastern Cooperative Oncology Group performance status and a maximum of one prior chemotherapy regimen, 600 mg/m2 was tolerated, but grade 3 or 4 neutropenia occurred in four of six patients who received an ADR-529 dose of 900 mg/m2 and in three of four patients at a dose of 750 mg/m2. Doxorubicin's estimated terminal half-life was 39.5 +/- 18.3 (mean +/- SD) hours; the area under the curve for plasma concentration of drug x time (AUC) was 1.74 +/- 0.40 (micrograms/microL) x hour. Total-body clearance was 598 +/- 142 microL/m2 per minute (N = 20), and it did not vary with ADR-529 dose. Estimated distribution and elimination phase half-lives for plasma ADR-529 were 0.46 +/- 0.30 hours and 4.16 +/- 2.94 hours, respectively. Total-body clearance was 111 +/- 87 microL/m2 per minute (N = 18); AUC was linear (r2 = .92), and the clearance rate was constant (r2 = .18) from 60 to 900 mg/m2. CONCLUSIONS: Myelotoxicity was dose limiting for ADR-529 at 600-750 mg/m2 when given with a fixed dose of doxorubicin at 60 mg/m2 (dose ratios of ADR-529 to doxorubicin ranged from 10:1 to 12.5:1). When used in combination, ADR-529 did not perturb doxorubicin's distribution, metabolism, or excretion; therefore, other mechanisms of cardioprotection must be involved. IMPLICATIONS: We recommend that an ADR-529 dose of 600 mg/m2 be given with single-agent doxorubicin at a dose of 60 mg/m2 in future studies.     

Effect of allyl alcohol-induced sublethal hepatic damage upon doxorubicin metabolism and toxicity in the rabbit

A model of hepatic dysfunction in vivo has been developed in rabbits to determine the effects of sublethal hepatocellular necrosis upon doxorubicin pharmacology. Eight New Zealand white rabbits were given 3 mg/kg doxorubicin i.v. Plasma doxorubicin and metabolite pharmacokinetics were determined and toxicity assessed by nadir complete blood counts. Hepatic function was assessed by the pulmonary excretion rate of 14CO2 from [14C]aminopyrine. Hepatocellular necrosis was produced by i.v. injection of 1.35 mg/kg of a 2% allyl alcohol solution. Doxorubicin administration and pharmacokinetics were repeated. Doxorubicin enhances the hepatotoxicity of allyl alcohol. Hepatocellular necrosis does not alter the plasma pharmacokinetics of doxorubicin but does increase the plasma exposure of doxorubicinol. Doxorubicin-induced myelosuppression is enhanced by allyl alcohol pretreatment. These data suggest that in circumstances of reduced hepatocellular volume or acute hepatocellular necrosis, a key plasma marker of doxorubicin-induced acute toxicity may be doxorubicinol.     

A pharmacokinetic and pharmacodynamic study of the new anthracycline pirarubicin in breast cancer patients

Summary We evaluated the pharmacokinetics of pirarubicin during 16 courses of therapy in 4 patients suffering from breast cancer who were treated with an association of pirarubicin (30–60 mg/m² according to the hematologic tolerance to the previous course, the first course being given at a dose of 40 mg/m²) and continuous infusions of 5-fluorouracil (750 mg/m² daily for 5 days). Pirarubicin's pharmacokinetics and metabolism were linear within this dose range; the metabolites identified were pirarubicinol, doxorubicin and doxorubicinol (AUC ratios of metabolite/pirarubicin were 0.6, 0.64 and 0.57 respectively). Pirarubicin's decay from plasma followed a twocompartmental pattern, showing half-lives of 15.6 min and 16.6 h: the total plasma clearance of the drug was 140 l/h^–1/m^–2, and the total volume of distribution was 2,830 l/m². A relationship was observed between some pharmacokinetic parameters and the toxic effects of the drug: the percentage of survival of granulocytes was significantly correlated with the AUC values for doxorubicin and doxorubicinol, whereas that of platelets was significantly correlated with the AUC values for pirarubicin and pirarubicinol. This is the first study to demonstrate a pharmacokinetic/pharmacodynamic relationship for pirarubicin.     

Results of a Phase I trial of sorafenib (BAY 43-9006) in combination with doxorubicin in patients with refractory solid tumors.

BACKGROUND: Sorafenib (BAY 43-9006), a novel, oral multi-kinase inhibitor, blocks serine/threonine and receptor tyrosine kinases in the tumor and vasculature. Sorafenib demonstrated single-agent activity in Phase I studies, and was tolerated and inhibited tumor growth in combination with doxorubicin in preclinical studies. This Phase I dose-escalation study determined the safety, pharmacokinetics and efficacy of sorafenib plus doxorubicin. PATIENTS AND METHODS: Thirty-four patients with refractory, solid tumors received doxorubicin 60 mg/m(2) on Day 1 of 3-week cycles, and oral sorafenib from Day 4 of Cycle 1 at 100, 200 or 400 mg bid. RESULTS: Common drug-related adverse events were neutropenia (56%), hand-foot skin reaction (44%), stomatitis (32%), and diarrhea (32%). The maximum tolerated dose was not reached. One patient with pleural mesothelioma achieved a partial response (modified WHO criteria) and remained on therapy for 39.7 weeks. Fifteen patients (48%) achieved stable disease for >/=12 weeks. Doxorubicin exposure increased moderately with sorafenib 400 mg bid. The pharmacokinetics of sorafenib and doxorubicinol were not affected. CONCLUSION: Sorafenib 400 mg bid plus doxorubicin 60 mg/m(2) was well tolerated. The increased doxorubicin exposure with sorafenib 400 mg bid did not result in significantly increased toxicity; low patient numbers make the clinical significance of this unclear. These promising efficacy results justify further clinical investigation.     

Serum concentrations of amiodarone required for an in vivo modulation of anthracycline resistance

We demonstrated previously that amiodarone is able to circumvent in vitro the inherent resistance to anthracyclines of the DHD/K12 rat colon cancer cell line. We have now determined in the rat the amiodarone seric concentrations required to enhance the in vitro cytotoxicity of 4'-deoxydoxorubicin (deoDX) against DHD/K12 cells. A maximal deoDX potentiation was obtained in vitro when anthracycline was diluted in the serum of rats receiving at least 75 mg/kg of intravenous amiodarone resulting in seric concentrations of more than 40 micrograms/ml. In patients treated with amiodarone, the mean serum concentrations were 0.9 +/- 0.1 microgram/ml after an one month's oral administration of 200 mg/day, 2.2 +/- 1.0 micrograms/ml after a 24 hr continuous infusion of 300 to 900 mg/day and 5.4 +/- 1.1 micrograms/ml after a brief 3 hrs infusion of 450 mg amiodarone. Such amiodarone concentrations in human serum are much lower than those necessary to produce a significant anthracycline potentiation. In rats receiving amiodarone at a maximal tolerated dose (100 mg/kg) minutes before the injection of 10 mg/kg doxorubicin (DX), we observed an increased accumulation of the anthracycline in the liver and kidney compared to rats receiving DX alone. The DX content was not modified by amiodarone in the other organs studied (heart, lung, spleen and pancreas). An amiodarone pretreatment accelerated the death of rats receiving 5 or 10 mg/kg DX did not provoke lethality for a lower dose of 2.5 mg/kg DX. The very high doses required and the risk of increased toxicity seem to preclude the use of amiodarone for the modulation of anthracycline resistance in cancer patients.