The influence of ranitidine on the pharmacokinetics and toxicity of doxorubicin in rabbits

Summary The influence of ranitidine on the pharmacokinetics and toxicity of doxorubicin was studied in six female New Zealand white rabbits. Plasma pharmacokinetic data were first obtained from rabbits given 3 mg/kg doxorubicin. After 1 month, the same rabbits were treated with ranitidine, 2.5 mg/kg or 25 mg/kg, before and during doxorubicin administration. The plasma doxorubicin assays to determine pharmacokinetic parameters were repeated. Drug toxicity was evaluated using complete blood counts, and hepatic function was measured using a ¹⁴C-aminopyrine breath test. High-dose ranitidine increased the total exposure to doxorubicin (area under the curve of doxorubicin alone =1.44±0.88 M·h/ml vs 4.49±2.35 M·hr/ml for doxorubicin given with high-dose ranitidine; P=0.06). Low-dose ranitidine did not alter doxorubicin pharmacokinetics. Exposure to doxorubicinol was altered by either high-dose or low-dose ranitidine. ¹⁴C-Aminopyrine half-life was altered by a raniditine dose of 25 mg/kg (aminopyrine half-life after placebo control =97±6 min as against aminopyrine half-life after ranitidine =121±7 min; mean±SEM; P<0.02). Low-dose ranitidine did not exacerbate doxorubicin-induced myelosuppression. High-dose ranitidine enhanced doxorubicin-induced erythroid suppression while sparing the myeloid series. At cytochrome P-450-inhibitory doses, ranitidine's effects upon doxorubicin plasma pharmacokinetics are similar to those previously seen with cimetidine. These changes did not appear to alter drug detoxification and are not related to microsomal inhibition of doxorubicin detoxification. Low doses of ranitidine do not alter doxorubicin plasma pharmacokinetics or toxicity in rabbits.Grant support: Glaxo Inc., Veterans Administration, NIH BRSG RR-05424, NIH Grant RR-00095, Clinical Research Center. American Cancer Society Institutional Grant IN25V     

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.     

The effect of cimetidine on cyclophosphamide metabolism in rabbits

Summary Six female rabbits were given 20 mg/kg cyclophosphamide (containing 100 Ci [³H-chloroethyl]-cyclophosphamide) alone or 1 h following 100 mg/kg cimetidine. Serial plasma and urine specimens were collected and levels of cyclophosphamide and its metabolites (4-hydroxycyclophosphamide, 4-ketocyclophosphamide, phosphoramide mustard, and carboxyphosphamide) were measured. 4-Ketocyclophosphamide was the major metabolite present in rabbit plasma and urine, with lesser amounts of 4-hydroxycyclophosphamide, carboxyphosphamide, and phosphoramide mustard also being identified. Cimetidine pretreatment resulted in prolongation of cyclophosphamide's half-life from 24.3±7.3 to 33.5±9.5 min (mean ± SD;P=0.036) but did not significantly alter the AUC_{0–8 h} for the latter drug. Cimetidine pretreatment resulted in a significantly greater AUC_{0–8 h} for 4-hydroxycyclophosphamide (189.4±77 vs 364.6±126.7 mol min/l^–1;P=0.016) as compared with control values. A higher AUC_{0–8 h} value for phosphoramide mustard (53.7±69.2 vs 95.7±34.7 mol min/l^–1) was also observed after cimetidine dosing but the difference was not significant (P=0.21). Kinetics of 4-ketocyclophosphamide and carboxyphosphamide were not significantly affected by cimetidine treatment. Cimetidine was added to hepatic microsomes isolated from phenobarbital-treated rabbits; it did not inhibit cyclophosphamide's metabolism in vitro, suggesting that its in vivo effect may be mediated through mechanisms other than cytochrome P-450 inhibition. Cimetidine pretreatment increases exposure to cyclophosphamide and its major activated metabolite, 4-hydroxycyclophosphamide. Potentiation rather than inhibition of cyclophosphamide's pharmacodynamic effect is to be predicted when cimetidine is given concomitantly with the former. Alterations in hepatic blood flow or mechanisms other than microsomal inhibition by cimetidine may explain this potentiation.Supported in part by the Department of Veteran Affairs and grant CA-49186 from the National Institutes of Health (NIH)Department of Clinical Pharmacology, Sun Yat-sen University of Medical Sciences, Guangzhou, People's Republic of China     

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.     

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     

Interaction of cimetidine with oral melphalan

Summary The effects of pretreatment with cimetidine (200 mg three times daily, 400 mg at night) on the pharmacokinetics of oral melphalan (10 mg) have been investigated in patients with multiple myeloma. Cimetidine pretreatment reduced the bioavilability of oral melphalan by approximately 30% (P<0.05). The elimination rate of melphalan from plasma was significantly increased by cimetidine (P<0.05), the half-life being reduced from 1.94±0.55 h to 1.57±0.53 h. Cimetidine appeared to reduce the interindividual variability in melphalan absorption, but at the cost of reduced bioavailability.The study described in this paper was supported by a grant from Smith Kline & French     

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.     

Effect of tamoxifen pretreatment on the pharmacokinetics, metabolism and cardiotoxicity of doxorubicin in female rats

The purpose of this study was to examine the effect of tamoxifen pretreatment on the metabolism and pharmacokinetics of doxorubicin. We tested the hypothesis that the pretreatment would counteract the side effects of doxorubicin and modify the disposition of the drug. The concentration-time profiles of doxorubicin in plasma and blood cells were determined in conjunction with the cumulative amount of renal and hepatobiliary elimination of unchanged drug and metabolites following a 10-day tamoxifen pretreatment at a dose of 1 mg/kg per day. Furthermore, under the same experimental protocol the serum concentration-time profile of endothelin was determined as a biomarker of toxicity. Methods: Female Sprague Dawley rats (225–275 g), pretreated orally for 10 days with corn oil or tamoxifen in corn oil (1 mg/kg per day), received ¹⁴C-doxorubicin (specific activity 0.4 μCi/mg, 10 mg/kg) intravenously. Plasma, blood cells, bile and urine were collected periodically and analyzed for doxorubicin and its metabolites. Four other groups of animals received the same pretreatment and non-labeled doxorubicin. Their serum samples were analyzed for endothelin. Two additional groups were also used to examine the effect of tamoxifen on the in vitro metabolism of doxorubicin by the cytosolic enzyme aldo-keto reductase. Results: Tamoxifen pretreatment reduced the total protein of the cytosolic fraction by 50% and reduced the formation of doxorubicinol both in vitro and in vivo. The pretreatment resulted in a notable increase in the area under plasma and blood cells concentration-time curves of doxorubicin and a significant reduction in mean residence time, apparent volume of distribution and serum endothelin levels. Conclusions: We attributed the increase in the area under the curves of plasma and blood cells following tamoxifen pretreatment to a reduction in the uptake of doxorubicin by peripheral tissues. This conclusion was consistent with the reduction in the volume of distribution of plasma, mean residence time and higher availability of the parent compound for excretion. An interesting observation was that the increase in concentration of doxorubicin in plasma was not concomitant with an increase in concentration of doxorubicinol. The levels of this toxic metabolite and its corresponding biliary rate constant were reduced by approximately 50%. The results demonstrate that tamoxifen, in addition to being a modulator of P-glycoprotein and counteracting the effects of doxorubicin at the cellular level, also alters the metabolic profile of doxorubicin either by inhibiting the formation of the toxic metabolite doxorubicinol or by reducing the enzyme responsible for the biotransformation. The change in metabolism may well be a contributing factor to reduction of serum endothelin levels. Received: 2 September 1999 / Accepted: 14 April 2000     

Phase I and pharmacokinetic trial of liposome-encapsulated doxorubicin

A total of 21 patients with advanced cancer were entered into a phase I study to determine the maximum tolerable dose (MTD) of liposome-encapsulated doxorubicin (LED) given weekly for 3 consecutive weeks at doses of 20, 30, or 37.5 mg/m² per week. For a comparison of the pharmacokinetic behavior of LED with that of standard-formulation doxorubicin, 13 patients received a dose of standard-formulation doxorubicin 2 weeks prior to the first dose of LED. All doses were given by 1-h infusion through a central vein. Toxicity was evaluated in 22 courses delivered to 17 patients. The MTD with this schedule was 30 mg/m² per week×3. The single patient treated at 37.5 mg/m² weekly could not complete the entire course due to myelosuppression. At the dose of 30 mg/m² per week, three of eight patients had grade 3 leukopenia. Other toxicities included mild to moderate thrombocytopenia, nausea, vomiting, fever, alopecia, diarrhea, fatigue, stomatitis, and infection. At the dose of 30 mg/m² per week, the total doxorubicin AUC and peak total doxorubicin concentrations in plasma were 8.75±8.80 M h (mean±SD) and 3.07±1.45 M, respectively, after LED administration. The total doxorubicin AUC and peak total doxorubicin concentrations in plasma were 3.92±2.47 M h and 2.75±2.70 M, respectively, after the infusion of standard-formulation doxorubicin. The total body clearance of doxorubicin was 18.42±11.23 l/h after the infusion of LED and 31.21±15.48 l/h after the infusion of standard-formulation doxorubicin. The mean elimination half-lives of doxorubicin were similar: 8.65±5.16 h for LED and 7.46±5.16 h for standard-formulation doxorubicin. Interpatient variability in pharmacokinetic parameters as demonstrated by the percentage of coefficients of variation was 33%–105%. There was no relationship between the percentage of WBC decrease or the duration of WBC suppression and the total doxorubicin or doxorubicinol AUC. There was no correlation between the duration of leukopenia and drug exposure as reflected by the AUC of liposome-associated doxorubicin. LED can be given in doses similar to those of standard-formulation doxorubicin and produces acute toxicities similar to those caused by standard doxorubicin.Abbreviations MTD maximum tolerable dose - LED liposome-encapsulated doxorubicin - AUC area under the plasma concentration x time curve - WBC white blood cell count - PLT platelet count - ECOG Eastern Cooperative Oncology Group - EKG electrocardiogram - MUGA multigated nuclide scan - CLTB total body clearance - PC phosphatidylcholine: PG, phosphatidylglycerol - PEG-DSPE polyethylene glycol conjugated to distearoyl phosphatidylethanolamine - HSPC hydrogenated soy phosphatidylcholine - chol cholesterol This work was supported by DHHS, NCl NO-l-CM 07 303 and by a Career Development Award from the American Cancer Society (to B. A. C.)     

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.     

Improved high-performance liquid chromatography assay of doxorubicin: Detection of circulating aglycones in human plasma and comparison with thin-layer chromatography

Summary We compared doxorubicin and metabolite pharmacokinetic data obtained from thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) assay of plasma samples from six patients who had been treated with doxorubicin. Duplicate 1-ml samples were extracted with chloroform: isopropanol (1:1) and assayed using a sensitive HPLC system incorporating a dual pump gradient with tetrahydrofuran as the mobile phase and fluorescence detection. Duplicate 1-ml samples from the same specimens were assayed using a modification of a previously described TLC assay. Areas under the curve for doxorubicin by HPLC (3.36±2.30 M · h) and TLC (4.16±2.50 M · h) were not significantly different (P=0.5). Terminal half-life of doxorubicin by HPLC (28.0±6.98 h) and TLC (23.2±7.8) (P=0.29) and the calculated total-body clearances by HPLC (0.55±0.29 l/min) and TLC (0.45±0.23) (P=0.55) were not significantly different. Areas under the curve for doxorubicinol by HPLC (2.75±1.4 M · h) and TLC (2.53±7.1 M · h) (P=0.73) showed no significant differences. HPLC detected a mixed 7-deoxydoxorubicinol aglycone-doxorubicin aglycone peak, 7-deoxydoxorubicin aglycone, and two nonpolar, unidentified metabolites. TLC detected the following aglycone metabolites: doxorubicin aglycone, doxorubicinol aglycone, 7-deoxydoxorubicinol aglycone, an unidentified polar metabolite, and several unidentified nonpolar metabolites. From these data we conclude that HPLC and TLC detect concentrations of doxorubicin and doxorubicinol from human plasma equally well to concentrations of 7.0 nM (4 pmol injected doxorubicin). Aglycones do circulate in human plasma at concentrations above the detection limits of both assays. Doxorubicinol aglycone, which is detected by TLC but not by HPLC, may be formed from artifactual breakdown of doxorubicinol during TLC development. Unidentified nonpolar compounds seen on HPLC and TLC may represent further doxorubicin metabolism than previously described.     

Epirubicin metabolism and pharmacokinetics after conventional- and high-dose intravenous administration: a cross-over study

In a pharmacokinetics study, six patients were treated i.v. with epirubicin (EPI) at the two dose levels of 60 and 120 mg/m², whereas a further six patients were treated at 75 and 150 mg/m². Both groups were studied according to a balanced cross-over design; the aim of the study was to assess the pharmacokinetic linearity of epirubicin given at high doses. Both the absolute goodness of fit and the Akaike Information Criterion (AIC) point to a linear, tricompartmental open model as the choice framework for discussing EPI plasma disposition after 16/24 administrations, independent of the delivered dose. After 8 treatments, the minimal AIC value corresponded to a nonlinear tissue-binding model. However, even in these cases, second-order effects were present only during the early minutes following treatment. In a model-independent framework, mean EPI plasma clearance was identical at the two dose levels of 60 and 120 mg/m² (65.4±8.0 vs 65.3±13.4 l/h,P=0.92). Both the mean residence time (MRT) and the volume of distribution at steady-state (V_ss) were similar as well (MRT: 22.6±2.9 vs 24.2±3.7 h;P=0.46; V_ss: 21.3±1.5 vs 22.6±6.5 l/kg,P=0.46). No statistically significant difference could be found in mean statistical-moment-theory parameters determined after 75- and 150-mg/m² EPI doses (plasma clearance, PICI: 83.4±13.5 vs 68.5±12.8 l/h,P=0.12; MRT: 22.6±4.8 vs 21.9±3.9 h,P=0.60; V_ss: 26.7±10.5 vs 21.2±7.0 l/kg,P=0.17). Analysis of variance also failed to reveal any significant correlation between dose and plasma clearance. However, when data relative to single patients were examined, a trend toward nonlinear drug distribution as well as a consequent increase in peripheral bioavailability could be observed in 4/6 patients of the 75-mg/m² vs the 150-mg/m² group. No significant dose-dependent variation was observed in the ratio between the molecular-weight-corrected areas under the concentration-time curve for the metabolites and those for EPI [60 vs 120 mg/m²: epirubicinol (EPIol), 0.23±0.10 vs 0.22±0.06,P=0.20; epirubicin glucoronide (G1), 0.46±0.14 vs 0.62±0.40,P=0.26; epirubicinol glucuronide (G2), 0.21±0.05 vs 0.30±0.16,P=0.06; and 75 vs 150 mg/m²: EPIol, 0.33±0.22 vs 0.32±0.19,P=0.42; G1, 0.51±0.23 vs 0.46±0.17,P=0.53; G2, 0.18±0.10 vs 0.22±0.10,P=0.34]. In conclusion, all the metabolic pathways seemed well preserved when the dose was doubled, and no evident sign of saturation kinetics could be found.     

Effect of the nonimmunosuppressive cyclosporin analog SDZ PSC-833 on colchicine and doxorubicin biliary secretion by the rat in vivo

Colchicine and doxorubicin are secreted into bile as a major pathway of their elimination. Colchicine and doxorubicin are also substrates for P-glycoprotein, and P-glycoprotein has been demonstrated to be present at the liver canalicular membrane. Cyclosporin (CsA) inhibits colchicine biliary secretion in vivo. In the present study, the effects of SDZ PSC-833, a nonimmunosuppressive cyclosporin D analog, on the biliary secretion of colchicine and doxorubicin were investigated. SDZ PSC-833 given at a bolus dose of 2 mg/kg promptly decreased colchicine biliary clearance from 9.05±0.2 to 2.41±0.43 ml min^–1 kg^–1 (P<0.001) and the colchicine bile/plasma ratio from 146±8 to 35±5 (P<0.001). SDZ PSC-833 also inhibited doxorubicin biliary clearance (basal: 10.5±3 vs post-SDZ PSC-833: 2.48±0.94 ml min^–1 kg^–1;P=0.06) and the doxorubicin bile/plasma ratio (basal: 228±64 vs post-SDZ PSC-833: 48±22;P<0.01). Colchicine renal secretion was completely inhibited by SDZ PSC-833. Thus, SDZ PSC-833 inhibits the constitutive transport of the multidrug-resistance substrates colchicine and doxorubicin and is more potent than cyclosporin in this regard. The possibility of increased toxicity to normal tissues because of impaired elimination of cytotoxic agents will need to be considered if SDZ PSC-833 is used to chemosensitize cancer cells.This work was supported in part by the Research Service, Department of Veterans Affairs     

Phase I and pharmacokinetics studies of prochlorperazine 2-h i.v. infusion as a doxorubicin-efflux blocker

In an earlier phase I study, we reported that the maximal tolerated dose (MTD) of prochlorperazine (PCZ) given as a 15-min i.v. infusion was 75 mg/m². The highest peak plasma PCZ concentration achieved was 1100 ng/ml. The present study was conducted to determine if PCZ levels high enough to block doxorubicin (DOX) efflux in vitro could be achieved and sustained in vivo by increasing the duration of i.v. infusion from 15 min to 2 h. The treatment schedule consisted of i.v. prehydration with at least 500 ml normal saline (NS) and administration of a fixed standard dose of 60 mg/m² DOX as an i.v. bolus over 15 min followed by i.v. doses of 75, 105, 135, or 180 mg/m² PCZ in 250 ml NS over 2 h. The hematologic toxicities attributable to DOX were as expected and independent of the PCZ dose. Toxicities attributable to PCZ were sedation, dryness of mouth, anxiety, akathisia, hypotension, cramps, and confusion. The MTD of PCZ was 180 mg/m². Large interpatient variation in peak PCZ plasma levels (91–3215 ng/ml) was seen, with the plasma half-life (t1/2) being approximately 57 min in patients given 135–180 mg/m² PCZ. The volume of distribution (V_d), total clearance (Cl_T), and area under the curve (AUC) were 350.1±183.8 l/m², 260.7±142.7 l m² h^–1 and 1539±922 ng ml h^–1, respectively, in patients given 180 mg/m² PCZ and the respective values for patients receiving 135 mg/m² were 48.9±23.76 l/m², 33.2±2.62 l m² h^–1, and 4117±302 ng ml h^–1. High PCZ plasma levels (>600 ng/ml) were sustained in all patients treated with 135 mg/m² PCZ for up to 24 h. DOX plasma elimination was biphasic at 135 and 180 mg/m² PCZ, and a>10-ng/ml DOX plasma level was maintained for 24 h. Partial responses were seen in three of six patients with malignant mesothelioma, in two of ten patients with non-small-cell lung carcinoma, and in the single patient with hepatoma. Our data show that PCZ can be safely given as a 2-h infusion at 135 mg/m² with clinically manageable toxicities. The antitumor activity of the combination of DOX and PCZ needs to be confirmed in phase II trials.This work was supported by NIH grant R01 CA-29360 and S1488, CRC grant M01 RR-05280, and the Joan Levy Cancer Foundation. This paper was presented at the meeting of the American Association for Cancer Research, Orlando, Florida, May 19–22, 1993     

Impact of body composition on pharmacokinetics of doxorubicin in children: a Glaser Pediatric Research Network study

Purpose  We studied the relationship between doxorubicin pharmacokinetics and body composition in children with cancer. Patients and methods  Children between 1 and 21 years of age, receiving doxorubicin as an infusion of any duration <24 h on either a 1-day or 2-day schedule were eligible if they had no significant abnormality of liver function tests, their dose of doxorubicin was not based on ideal body weight or otherwise “capped,” and they weighed ≥12 kg. Body composition was measured by dual-energy X-ray absorptiometry. Doxorubicin and doxorubicinol concentration in plasma were measured by high pressure liquid chromatography. NONMEM was used to perform pharmacokinetic model fitting and S-PLUS was used to perform a post hoc analysis to examine the effect of body composition on pharmacokinetic parameters. Results  Twenty-two subjects (16 male; 10 Hispanic, 10 Caucasian, 2 Asian) completed the study. The median age was 15.0 years (range 3.3–21.5), median weight was 51.5 kg (range 12.4–80), median BMI was 19.7 (range 13.2–30.0), and median body fat was 25% (range 15–36). The population mean clearance of doxorubicin was 420 ml/min/m². Doxorubicinol but not doxorubicin clearance was lower in patients with body fat greater than 30%. Conclusions  Doxorubicinol clearance is decreased in children with >30% body fat. This finding is potentially important clinically, because doxorubicinol may contribute significantly to cardiac toxicity after doxorubicin administration. Further study of the body composition on doxorubicin and doxorubicinol pharmacokinetics and on clinical outcomes is warranted.     

Doxorubicin and doxorubicinol: intra-and inter-individual variations of pharmacokinetic parameters

Summary Doxorubicin was given by short i. v. infusion (dose range 25–72 mg/m²) to 18 patients who underwent three to seven successive courses of chemotherapy (total, 57 courses). Plasma levels of doxorubicin and its major metabolite doxorubicinol were determined by high-performance liquid chromatography over a 48-h period after the infusion. Pharmacokinetic parameters for the parent drug and its metabolite were calculated for each course of treatment. The results show considerable inter-and intraindividual variations for most parameters. The coefficients of variation (CV) ranged from 37% to 93% (inter-individual) and from 6% to 59% (intra-individual). Nevertheless, we observed a good stability over successive courses for terminal half-life in six patients (CV, 6%–25%) and for clearance and AUC in four subjects (CV, 10%–22%). The ratio of the AUCs for doxorubicinol: doxorubicin averaged 0.514. The pharmacokinetic pattern of doxorubicinol was biphasic in plasma of the majority of patients. We propose a model for curve-fitting of these metabolite plasma concentrations that is based on two successive releases of the compound in the plasma compartment, separated by a lag time.     

Biliary excretion of 17-(allylamino)-17-demethoxygeldanamycin (NSC 330507) and metabolites by Fischer 344 rats

PURPOSE: Although dexrazoxane (ICRF-187) is used clinically to protect against doxorubicin cardiotoxicity, the age-related effect of dexrazoxane on doxorubicin pharmacokinetics has not been well studied. METHODS: We therefore examined the effect of pretreatment with dexrazoxane (50 mg kg(-1) i.p. 1 h prior to administration of doxorubicin 2 mg kg(-1) i.v. bolus) on doxorubicin and doxorubicinol pharmacokinetics in Fischer 344 rats at 5 months of age (young adult) and 22 months of age (old). RESULTS: Dexrazoxane had no major effects on doxorubicin or doxorubicinol pharmacokinetics in plasma or heart in either young or old rats. However, age had significant effects on anthracycline pharmacokinetics. Early plasma concentrations were increased and systemic clearance of doxorubicin was decreased in old compared with young rats. Cardiac concentrations of doxorubicin (AUC) were significantly increased in old rats. In addition cardiac doxorubicinol concentrations (AUC 0-72 h) were increased by over 80% in old compared to young rats. CONCLUSION: The results suggest that dexrazoxane does not alter doxorubicin pharmacokinetics. In contrast, aging in the rat model is associated with altered doxorubicin and doxorubicinol pharmacokinetics, in particular in the heart. These changes could increase the risk of anthracycline cardiotoxicity with age.     

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.     

A new procedure for the preparation of liposomal doxorubicin: biological activity in multidrug-resistant tumor cells

We describe a new procedure for the preparation of liposomal doxorubicin. Doxorubicin can be efficiently complexed to preformed or lyophilized cardiolipin-containing liposomes. Complex formation was performed by vigorous vortexing. As much as 96.8% of the initial drug quanitty may be bound to those liposomes under optimal incubation conditions (4 h at 37°C). The binding study showed the presence of two levels of specific binding (dissociation constants, 28±8 M and 1.0±0.3 mM). The drug is firmly integrated in the liposome-membrane lipid bilayer rather than binding at the surface. Cytotoxicity studies using tumor cells revealed efficient drug delivery using liposome-complexed doxorubicin. This new liposomal doxorubicin preparation reverses multidrug resistance in MCF-7/ADR and CH LZ cells at levels equivalent to that obtained with a previously described liposome-encapsulated doxorubicin preparation, showing that the drug is integrated as well in the liposome carrier and is transported as well into cells. Increased concentration of liposomes at the subcytotoxic level in liposome-complexed doxorubicin enhances drug cytotoxicity in multidrug-resistant CH LZ cells as compared with liposome-encapsulated drug. This new preparation for liposomal doxorubicin may be carried out immediately prior to clinical administration, offering advantages in terms of cost and stability.Abbreviations Dox Doxorubicin - Lip liposomes - Dox-Lip liposomally encapsulated doxorubicin - Dox+Lip liposomally associated doxorubicin - MDR multidrug resistance     

Gender affects doxorubicin pharmacokinetics in patients with normal liver biochemistry

We studied the variability in doxorubicin pharmacokinetics in 27 patients, all of whom had normal liver biochemistry tests. Blood samples were collected after the first cycle of single-agent doxorubicin given as an i.v. bolus and plasma levels were measured by high-performance liquid chromatography (HPLC). The relationship of doxorubicin clearance (dose/AUC) with biochemical tests (AST, bilirubin, alkaline phosphatase, albumin, creatinine) and physical characteristics (age, gender, height, weight, tumour type) was investigated. The 6 men had a significantly higher doxorubicin clearance than did the 21 women (median values, 59 and 27 lh^–1 m^–2, respectively;P=0.002). Doxorubicin clearance was significantly lower in patients with breast cancer than in those with other tumours (median values, 26 and 53 lh^–1 m^–2, respectively;P=0.0008). The other biochemical and physical parameters did not correlate with doxorubicin clearance. However, in multivariate analysis, gender was the only factor predicting doxorubicin clearance (r ²=40%). The ratio of the AUCs for doxorubicinol and doxorubicin (R) was higher in the men than in the women (median values, 0.62 and 0.36, respectively;P=0.03). We conclude that gender may be an important determinant of doxorubicin clearance in patients with normal liver biochemistry.