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.     

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     

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.     

Daunorubicin and daunorubicinol pharmacokinetics in plasma and tissues in the rat

Recent evidence suggests that 13-hydroxy metabolites of anthracyclines may contribute to cardiotoxicity. This study was designed to determine the pharmacokinetics of daunorubicin and the 13-hydroxy metabolite daunorubicinol in plasma and tissues, including the heart. Fisher 344 rats received 5 mg kg^–1 daunorubicin i.v. by bolus injection. Rats were killed at selected intervals for up to 1 week after daunorubicin administration for determination of concentrations of daunorubicin and daunorubicinol in the plasma, heart, liver, kidney, lung, and skeletal muscle. Peak concentrations of daunorubicin were higher than those of daunorubicinol in the plasma (133±7 versus 36±2 ng ml^–1;P<0.05), heart (15.2±1.4 versus 3.4±0.4 g g^–1;P<0.05), and other tissues. However, the apparent elimination half-life of daunorubicinol was longer than that of daunorubicin in most tissues, including the plasma (23.1 versus 14.5 h) and heart (38.5 versus 19.3 h). In addition, areas under the concentration/time curves (AUC) obtained for daunorubicinol exceeded those found for daunorubicin in almost all tissues, with the ratios being 1.9 in plasma and 1.7 in the heart. The ratio of daunorubicinol to daunorubicin concentrations increased dramatically with time from <1 at up to 1 h to 87 at 168 h in cardiac tissue. Thus, following daunorubicin injection, cumulative exposure (AUC) to daunorubicinol was greater than that to daunorubicin in the plasma and heart. If daunorubicinol has equivalent or greater potency than daunorubicin in causing impairment of myocardial function, it may make an important contribution to the pathogenesis of cardiotoxicity.     

Plasma and cerebrospinal fluid pharmacokinetics of cytosine arabinoside in dogs

Summary Cytosine arabinoside (ara-C) is a component of many protocols for the treatment of CNS (central nervous system) leukemia and lymphoma in humans and dogs. It is also used for the prophylaxis of CNS metastasis in acute lymphoblastic leukemia. Although ara-C enters the cerebrospinal fluid (CSF) of human cancer patients after i.v. administration, it is unclear whether a similar CNS distribution occurs in humans whose blood-brain barrier has not been compromised by invasive disease. No information on the penetration of ara-C into the CSF in dogs is available. We studied the plasma and CSF pharmacokinetics of 600 mg/m² ara-C in ten healthy male dogs after its administration as a rapid i.v. bolus (six dogs) or as a 12-h i.v. infusion (four dogs). Ara-C concentration in blood and CSF samples was determined by high-performance liquid chromatography (HPLC). After an i.v. bolus of ara-C, the mean plasma distribution half-life was 7.1±4.5 min and the mean elimination half-life was 69±28 min. The mean plasma clearance was 227±125 ml min^–1 m^–2. The peak concentration of ara-C in the CSF was 29±11 m, which occurred at 57±13 min after the ara-C bolus. The CSF elimination half-life was 113±26 min. During a 12-h infusion of ara-C (50 mg m^–2 h^–1), the plasma steady-state concentration was 14.1±4.2 m, the CSF steady-state concentration was 8.3±1.1 m, and the CSF: plasma ratio was 0.62±0.14. The plasma eleimination half-life was 64±19 min and the plasma clearance was 214±69 ml min^–1 m^–2. The CSF elimination half-life was 165±28 min. No clinically significant toxicity was observed over a 21-day period following drug administration in either of the treatment groups. Our data indicate that ara-C crosses the blood-brain barrier in normal dogs and that i.v. administration of this drug has potential as a treatment modality for neoplasia involving the CNS.Supported by the Canine Disease Research Fund and in part by the Elsa U. Pardee Foundation     

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.)     

Comparative pharmacokinetics of doxorubicin given by three different schedules with equal dose intensity in patients with breast cancer

Summary The pharmacokinetics of doxorubicin given according to three different schedules with a similar dosetime intensity have been studied and compared in 16 women with metastatic breast cancer. Six patients were treated with doxorubicin 75 mg/m² by i.v. bolus repeated every 3 weeks; 5 patients received doxorubicin by 4-day continuous infusion every 3 weeks (4 at 75 mg/m² and 1 at 60 mg/m²); 5 patients received 25 mg/m² by i.v. bolus given weekly. Timed blood samples were collected and plasma levels of doxorubicin and its metabolite doxorubicinol were measured by high-performance liquid chromatography with fluorescence detection. Peak plasma concentrations were measured, and areas under the concentration-time curves calculated. Peak plasma levels of doxorubicin were significantly lower with the 4-day infusion than with either of the bolus injections. The 4-day infusion, however, gave significantly greater total exposure to doxorubicin and doxorubicinol, as indicated by area under the concentration-time curve, than weekly or 3-weekly bolus treatment. A single bolus injection of doxorubicin 25 mg/m² yielded a total exposure to doxorubicin approximately half that achieved with a 75 mg/m² bolus injection. Over a 3-week period, therefore, total exposure to doxorubicin would be greater with the weekly low-dose schedule than with the 3-weekly administration. We conclude that drug scheduling has significant effects on doxorubicin pharmacokinetics.     

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 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     

Cellular pharmacokinetics of doxorubicin in patients with chronic lymphocytic leukemia: comparison of bolus administration and continuous infusion

The purpose of this study was to determine whether administration of doxorubicin (DOX) as a continuous infusion or a bolus injection resulted in similar leukemic cell drug concentration in patients with refractory chronic lymphocytic leukemia (CLL). This study was carried out on five patients with refractory CLL, with DOX administered either as a bolus injection (35 mg/m²; CHOP protocol) or as a constant-rate infusion for a period of 96 h (9 mg/m² per day; VAD protocol). The two types of drug administration were used alternatively with the same patient. Plasma and cellular DOX concentration were determined using high-performance liquid chromatography. Peak plasma DOX levels were higher after the bolus injection than after continuous administration (1509±80 ng/ml vs 11.6±1.8 ng/ml, respectively), whereas the plasma area under the curve (AUC) levels were similar. Maximum DOX cellular concentrations were 8629±2902 ng/10⁹ cells (bolus injection) and 2745±673 ng/10⁹ cells (96 h infusion). The cellular AUC after the bolus injection was 2.85 times greater than that observed after continuous administration. This difference was due to a higher cellular peak level followed by a relatively prolonged retention of the drug, with a loss of only 25% in the first 24 h following. These findings demonstrated that in CLL the cellular DOX exposure can be notably modified by the method of drug administration, with higher drug intracellular concentrations being achieved after bolus administration than with the infusion schedule.     

Bioavailability and pharmacokinetics of the cardioprotecting flavonoid 7-monohydroxyethylrutoside in mice

Purpose The pharmacokinetics and bioavailability of monoHER, a promising protector against doxorubicin-induced cardiotoxicity, were determined after different routes of administration.Methods Mice were treated with 500 mg.kg^–1 monoHER intraperitoneally (i.p.), subcutaneously (s.c.) or intravenously (i.v.) or with 1000 mg.kg^–1 orally. Heart tissue and plasma were collected 24 h after administration. In addition liver and kidney tissues were collected after s.c. administration. The levels of monoHER were measured by HPLC with electrochemical detection.Results After i.v. administration the AUC_{0–120 min} values of monoHER in plasma and heart tissue were 20.5±5.3 mol.min.ml^–1 and 4.9±1.3 mol.min.g^–1 wet tissue, respectively. After i.p. administration, a mean peak plasma concentration of about 130 M monoHER was maintained from 5 to 15 min after administration. The AUC_{0–120 min} values of monoHER were 6.1±1.1 mol.min.ml^–1 and 1.6±0.4 mol.min.g^–1 wet tissue in plasma and heart tissue, respectively. After s.c. administration, monoHER levels in plasma reached a maximum (about 230 M) between 10 and 20 min after administration. The AUC_{0–120 min} values of monoHER in plasma, heart, liver and kidney tissues were 8.0±0.6 mol.min.ml^–1, 2.0±0.1, 22.4±2.0 and 20.5±5.7 mol.min.g^–1, respectively. The i.p. and s.c. bioavailabilities were about 30% and 40%, respectively. After oral administration, monoHER could not be detected in plasma, indicating that monoHER had a very poor oral bioavailability.Conclusions MonoHER was amply taken up by the drug elimination organs liver and kidney and less by the target organ heart. Under cardioprotective conditions (500 mg/kg, i.p.), the C_max was 131 M and the AUC was 6.3 M.min. These values will be considered endpoints for the clinical phase I study of monoHER.     

Phase I clinical and pharmacokinetic study of cyclophosphamide administered by five-day continuous intravenous infusion

Summary A total of 14 patients, 7 male and 7 female, received in all 21 evaluable courses of cyclophosphamide administered by 5-day continuous infusion. Cyclophosphamide doses were escalated from 300 to 400 mg/m² per day for 5 days and repeated every 21–28 days. The patient population had a median age of 55 years (range 38–76) and a median Karnofsky performance status of 80 (range 60–100). Only 1 patient had not received prior therapy; 5 patients had received only prior chemotherapy, 1 had received only prior radiotherapy, and 7 had received both. Tumor types were gastric (1), lung (2), colon (4), urethral adenocarcinoma (1), cervical (2), chondrosarcoma (1), melanoma (1), uterine leiomyosarcoma (1), and pancreatic (1). The dose-limiting toxicity was granulocytopenia, with median WBC nadir of 1700/l (range 100–4800) in 8 heavily pretreated patients treated at 350 mg/m² per day for 5 days. One patient without heavy prior treatment received two courses at 400 mg/m² and had WBC nadirs of 800/l and 600l. WBC nadirs occurred between days 9 and 21 (median 14). Drug-induced thrombocytopenia occurred in only one patient (350 mg/m² per day, nadir 85000/l). Neither hyponatremia nor symptomatic hypoosmolality was observed. Radiation-induced hemorrhagic cystitis may have been worsened in one patient. Nausea and vomiting were mild. Objective remissions were not observed. The maximum tolerated dose for previously treated patients is 350 mg/m² per day for 5 days. This dose approximates the doses of cyclophosphamide commonly used with bolus administration. Plasma steady-state concentrations (Css) of cyclophosphamide, measured by gas liquid chromatography, were 2.09–6.79 g/ml. Steady state was achieved in 14.5±5.9 h (mean ±SD). After the infusion, cyclophosphamide disappeared from plasma monoexponentially, with a t^1/2 of 5.3±3.6 h. The area under the curve of plasma cyclophosphamide concentrations versus time (AUC) was 543±150 g/ml h and reflected a cyclophosphamide total-body clearance (CL_TB) of 103±31.6 ml/min. Plasma alkylating activity, assessed by p-nitrobenzyl-pyridine, remained steady at 1.6–4.3 g/ml nor-nitrogen mustard equivalents. Urinary excretion of cyclophosphamide and alkylating activity accounted for 9.3%±7.6% and 15.1%±2.0% of the administered daily dose, respectively. The t^1/2 and AUC of cyclophosphamide associated with the 5-day continuous infusion schedule are similar to those reported after administration of cyclophosphamide 1500 mg/m² as an i.v. bolus. The AUC of alkylating activity associated with the 5-day continuous infusion of cyclophosphamide is about three times greater than the AUC of alkylating activity calculated after a 1500-mg/m² bolus dose of cyclophosphamide. Daily urinary excretions of cyclophosphamide and alkylating activity associated with the 5-day continuous infusion schedule are similar to those reported after bolus doses of cyclophosphamide.     

The effects of cimetidine upon the plasma pharmacokinetics of doxorubicin in rabbits

Summary Cimetidine is an H₂ antagonist which inhibits cytochrome P-450 and reduces hepatic blood flow. To determine whether cimetidine interferes with the plasma pharmacokinetics of doxorubicin, we gave six female New Zealand rabbits doxorubicin 3 mg/kg, followed a month later by cimetidine 120 mg/kg every 12 h over 72 h and doxorubicin 3 mg/kg. Serial plasma specimens were obtained over 72 h and assayed for doxorubicin and its metabolites by high-performance liquid chromatography and fluorescence detection.Doxorubicin plasma pharmacokinetics were prolonged after cimetidine pretreatment [AUC 0.76±0.22 vs. 2.85±1.22 M×h, no pretreatment vs pretreatment (p=0.005), half-life=11.7±6.55 vs 28.0±8.16 h (P=0.0002), and clearance=0.129±0.036 vs 0.036±0.0111/min^-1 kg^-1 (P=0.0007)]. No significant differences were found between the AUCs for doxorubicinol, 7-deoxy doxorubicinol aglycone, or two unidentified nonpolar metabolites in nonpretreatment and pretreatment studies. Cimetidine increases and prolongs the plasma exposure to doxorubicin in rabbits. Doxorubicin metabolism does not appear to be affected by cimetidine.Grant Support Veterans Administration, NIH Grant RR-05424 and Clinical Research Center Grant RR-00095 American Cancer Society Institutional Grants #IN25V and IN24V, and JFCF #649     

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.     

Steady-state plasma concentrations and effects of taxol for a 250 mg/m2 dose in combination with granulocyte-colony stimulating factor in patients with ovarian cancer

Taxol, a natural product initially isolated from the stem bark of the western yewTaxus brevifolia, is undergoing phase II and III evaluation due to its reported activity against a variety of tumors. Previous studies have described correlations between plasma concentrations and toxicity when taxol is given (a) at lower doses, (b) for shorter infusion times, and (c) without granulocyte-colonystimulating factor. Because the 24-h infusion schedule is most commonly used in current clinical trials, we attempted to correlate steady-state plasma concentrations of taxol achieved with a 24-h continuous i.v. infusion with toxicities and responses. Plasma samples from 48 refractory ovarian cancer patients were obtained 1–2 h prior to the end of the first taxol infusion. Taxol concentrations were measured by high-performance liquid chromatography (HPLC). Interpatient variation of taxol plasma concentrations was small (mean±SD, 0.85±0.21 M. Total taxol body clearance was 256±72 ml min^–1m^–2 (mean±SD). Taxol plasma protein binding was 88.4%±1.3% (mean±SD,n=9). Grade 3–4 hematologic toxicity, mainly leukopenia, occurred in 92% of the patients. The leukopenia was transient and did not warrant a reduction in the dose of taxol. Grade 3–4 nonhematologic toxicity occurred in 8% of the patients. No severe hypersensitivity reaction or grade 3–4 neurotoxicity was observed. Correlations of plasma concentrations and toxicities were not feasible due to the high frequency of hematologic effects and the low frequency of nonhematologic toxicity. The low degree of interpatient variation in plasma concentrations hindered the development of correlations with response.     

Cellular and plasma adriamycin concentrations in long-term infusion therapy of leukemia patients

Summary To determine whether long-term adriamycin (ADM) infusions resulted in cellular ADM concentrations at least comparable to those observed after bolus injections, ADM cellular and plasma concentrations were measured in 18 patients with leukemia. ADM was administered at 30 mg/m² per day for 3 days, either as bolus injections or as 4-, 8-, or 72-h infusions. Negligible accumulation of plasma ADM was observed. Peak plasma ADM concentrations after bolus injections were 1640±470 ng/ml (n=7). Maximum levels were 176±34 ng/ml during 4-h infusion (n=5); 85±50 ng/ml during 8-h infusion (n=4); and 47±5 ng/ml (n=2) after 72-h infusion. ADM concentrations in nucleated blood and bone marrow cells correlated well (r=0.82, n=47). ADM accumulated in leukemic cells up to 30–100 times the plasma concentrations. The shorter the administration time-span, the higher the peak leukemic cell concentration and the greater the loss of drug immediately after the end of the administration. The final cellular ADM half-life was approximately 85–110 h. After long-term infusion and bolus injection of the same dose, similar areas under the curve for plasma or leukemic blast cell ADM concentrations were attained. Since comparable therapeutic efficacy was observed in all regimens, the antileukemic effect appeared not to be related to the peak plasma concentrations, while acute toxicity phenomena decreased with increasing duration of the infusion. Long-term ADM infusion deserves more attention in the treatment of patients with anthracyclines.Supported by the Queen Wilhelmina Foundation (The Netherlands Cancer Foundation, grant SNUKC 82-7), The Ank van Vlissingen Foundation and The Maurits and Anna de Kock Foundation     

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     

Pharmacokinetics of VP16-213 given by different administration methods

Summary Plasma pharmacokinetics of VP16-213 were investigated after a 30–60 min infusion in 14 adult patients and six children. In adults the elimination half-life (T_1/2 ), plasma clearance (Cl_p) and volume of distribution (Vd) were respectively 7.05±0.67 h, 26.8±2.4 ml/min/m², and 15.7±1.8 l/m²; in children 3.37±0.5 h, 39.34±6.6 ml/min/m², and 9.97±3.7 l/m². After repeated daily doses no accumulation of VP16-213 was found in plasma. The unchanged drug found in the 24 h urine after administration amounted to 20–30% of the dose.In eight choriocarcinoma patients plasma levels of VP16-213 were measured after oral capsules and drinkable ampoules. The bioavailability compared to the i.v. route was variable, mean values being 57% for capsules and 91% for ampoules. In one further patient, with abnormal d-Xylose absorption results, VP16-213 was not detectable in plasma after the oral ampoule dose.Steady state levels investigated in three patients after 72 h continuous VP16-213 infusion (100 mg/m²/24 h) were around 2–5 g/ml. Levels of VP16-213 were undetectable in CSF after i.v. or oral administration.     

Disposition of total and unbound etoposide following high-dose therapy

Total and unbound etoposide pharmacokinetics were studied in 16 adult patients (median age, 34 years; range, 18–61 years) undergoing autologous bone marrow transplantation for advanced lymphoma after receiving high-dose etoposide (35–60 mg/kg) as a single intravenous infusion. Pretreatment values for mean serum albumin and total bilirubin were 3.0±0.4 g/dl and 0.5±0.4 mg/dl, respectively. Etoposide plasma concentrations and protein binding (% unbound) were determined by high-performance liquid chromatography (HPLC) and equilibrium dialysis, respectively. Pharmacokinetic parameters for unbound and total etoposide were calculated by nonlinear regression analysis using a two-compartment model. Te mean (±SD) parameters for total etoposide included: clearance (CL), 31.8±17.7 ml min^–1 m^–2; volume of distribution (V_ss), 11.5±5.9 l/m², and terminal half-life (t _1/2 ), 7.2±3.7 h. Mean unbound CL was 209.6±62.7 ml min^–1 m^–2 and %unbound was 16%±5%. The mean etoposide %unbound was inversely related to serum albumin (r ²=0.45,P=0.0043). The mean %unbound at the end of the etoposide infusion was higher than that at the lowest measured concentration (21% vs 13%, respectively;P=0.017), suggesting that concentration-dependent binding may occur after high etoposide doses. The median total CL was higher in patients with serum albumin concentrations of 3.0 g/dl than in those with levels of >3.0 g/dl (34.6 vs 23.5 ml min^–1 m^–2,P=0.05). Total CL was directly related to %unbound (r ²=0.61,P=0.0004). Unbound CL was unrelated to either serum albumin or %unbound. These results demonstrate that hypoalbuminemia is independently associated with an increased etoposide %unbound and rapid total CL after the administration of high-dose etoposide. Unbound CL in hypoalbuminemic patients is unchanged in the presence of normal total bilirubin values.This study was supported in part by Bristol-Myers. Oncology Division