Pharmacokinetic analysis of rhein in Rheum undulatum L

This research aims to identify the main active compounds of Rhei undulati Rhizoma (roots of Rheum undulatum LINNE) and determine the types of anthraquinones absorbed into the body and their pharmacokinetic parameters. The boiling-water extract of the herb was administered to 12 healthy volunteers (9 men/3 women) at a dosage of 100 mg/kg the anthraquinone levels in plasma were determined with TLC, HPLC, and LC-MS. Rhein was the only anthraquinone compound absorbed by the body as determined for plasma analysis of the volunteers. The elimination rate constant of rhein in Rhei undulati Rhizoma was 0.23+/-0.02/h and the half life was 3.38+/-0.35 h. This experiment confirmed that rhein is the most important active compound absorbed by the body among anthraquinones contained in Rhei undulati Rhizoma, indicating that rhein is a promising marker substance to evaluate Rhei Rhizoma and Rhei undulati Rhizoma.

[Determination of rhein in plasma of rat by HPLC/MS]

A HPLC/MS method has been established for the determination of rhein in rat plasma, using an Alltima C18 column (4.6 x 250 mm, 5 microns) and a mixture of ACN-water (60:40) as the mobile phase, at the flow rate of 0.8 ml/min with the column temperature at 25 degrees C. The results showed that the level of rhein distributed in plasma reached the max value 0.5 h after the oral administration, and maintained a relatively high value from 0.25 h to 1.5 h. The method possessed high selectivity and sensitivity.

Anti-stress and anti-fatigue effects of fermented rice bran

The anti-stress and anti-fatigue effects on rats and mice of a hot water extract of rice bran fermented with Saccharomyces cerevisae IFO 2346 were investigated. Oral administration (1 g/kg/day) of the hot water extract of fermented rice bran (FRB) inhibited major changes in the weight of the adrenal, thymus, spleen and thyroid, showing an anti-stress effect. The hot water extract of FRB also inhibited increases in the GPT and LDH activity, cholesterol and glucose in the serum. The administration (1 g/kg/day) for 2 weeks significantly prolonged the swimming time, resulting in an increase in the anti-fatigue effect. It is considered from these results that FRB had anti-stress and anti-fatigue effects.

Elimination pathways of [14C]losoxantrone in four cancer patients

Losoxantrone is an anthrapyrazole derivative in Phase III development in the U.S. for solid tumors, notably breast cancer. To obtain information on the routes of elimination of the drug, a study was conducted in four patients with advanced solid tumors, which involved intravenous administration of 100 microCi of [14C]losoxantrone for a total dose of 50 mg/m(2) during the first course of losoxantrone therapy. Blood, urine, and feces were collected for up to 2 weeks and were analyzed for total radioactivity and parent drug. In addition, feces were profiled for the presence of metabolites. Plasma concentrations of total radioactivity exhibited a temporal pattern similar to the parent drug. Combined recovery of administered total radioactivity from urine and feces was 70% with the majority (87%) of this radioactivity excreted in the feces, presumably via biliary excretion. Feces extracts were profiled for metabolites using a high-performance liquid chromatography method developed to separate synthetic standards of previously identified human urinary metabolites. Only intact losoxantrone was found in the feces. About 9% of the dose was excreted in the urine, primarily during the first 24 h and mostly in the form of parent compound. Collectively, these data indicate that fecal excretion of unmetabolized drug via biliary and/or intestinal excretion is the primary pathway of intravenously administered losoxantrone elimination in cancer patients with refractory solid tumors.

Pharmacodynamic and pharmacokinetic studies of anthraquinone 2-carboxylic acid on passive cutaneous anaphylaxis in rats

The objectives of this study are to describe the inhibitory effect of 9,10-anthraquinone 2-carboxylic acid (AQCA) on IgE-mediated passive cutaneous anaphylaxis (PCA) reaction, and the pharmacokinetics of AQCA. Pharmacodynamic assessments were performed at 0.5, 1 and 2 mg/kg (i.v.) and 5, 10 and 20 mg/kg (p.o) dose levels. In separate groups, pharmacokinetics were assessed at 5 mg/kg (i.v.) and 5, 10, and 20 mg/kg (p.o.) dose levels. Intravenous and oral administration of AQCA inhibited the PCA reaction in rats in a dose-dependent manner. The PCA-inhibitory activity of AQCA (20 mg/kg) lasted more than 12 hrs after oral administration. The oral bio-availability decreased with increasing dosage, from 96% (5 mg/kg) to 81% (10 and 20 mg/kg). The absorption after oral administration was prolonged with Tmax values ranging from 1 to 6 h; while t(1/2) (4.8-16 h) values appeared to be comparable. These results suggest that AQCA has a potent and long acting anti-PCA activity. It is likely to be therapeutically useful in the treatment of asthma.

High-performance liquid chromatographic analysis of AQ4N, an alkylaminoanthraquinone N-oxide

A simple, highly selective and reproducible reversed-phase high-performance liquid chromatography method has been developed for the analysis of the new anti-cancer pro-drug AQ4N. The sample pre-treatment involves a simple protein precipitation protocol, using methanol. Chromatographic separations were performed using a HiChrom HIRPB (25 cmX4.6 mm I.D.) column, with mobile phase of acetonitrile-ammonium formate buffer (0.05 M) (22:78, v/v), with final pH adjusted to 3.6 with formic acid. The flow-rate was maintained at 1.2 ml min(-1). Detection was via photodiode array performed in the UV range at 242 nm and, since the compounds are an intense blue colour, in the visible range at 612 nm. The structurally related compound mitoxantrone was used as internal standard. The validated quantification range of the method was 0.05-10.0 microg ml(-1) in mouse plasma. The inter-day relative standard deviations (RSDs) (n=5) ranged from 18.4% and 12.1% at 0.05 microg ml(-1) to 2.9% and 3.3% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The intra-day RSDs for supplemented mouse plasma (n=6) ranged from 8.2% and 14.2% at 0.05 microg ml(-1) to 7.6% and 11.5% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The overall recovery of the procedure for AQ4N was 89.4 +/- 1.77% and 76.1 +/- 7.26% for AQ4. The limit of detection was 50 ng ml(-1) with a 100 microl sample volume. The method described provides a suitable technique for the future analysis of low levels of AQ4N and AQ4 in clinical samples.

Alteration in bilirubin excretion in individuals chronically exposed to arsenic in Mexico

We have studied hepatic function in individuals chronically exposed to arsenic (As) via drinking water in Region Lagunera, Mexico. We studied 51 individuals living in three villages exposed to As in water. Nazareno (0.014 mgAs/l), Santa Ana (0.1 mgAs/l) and Benito Juárez (0.3 mgAs/l). We determined the serum activity of aspartate aminotransferase (SAT) and alanine aminotransferase (ALT) as indicators of hepatocellular injury and that of gamma-glutamyl-transpeptidase (GGT) and alkaline phosphatase (ALP) as indicators of cholestasic injury. Serum bilirubin was used as an indicator of organic conjugated anion transport. Total proteins, albumin and globulin fraction in serum were used as indicators of biosynthetic liver capacity. The main findings of this study were the predominantly conjugated hyperbilirubinemia and increased serum ALP activity which were related to the concentration of total arsenic (TAs) in urine, suggesting the presence of cholestasis in As-exposed individuals. No significant changes were observed in the other parameters studied.

Suppressive effect of cyclophosphamide-induced toxicity by Withania somnifera extract in mice

Administration of Withania somnifera extract (Solanaceae) was found to significantly reduce leucopenia induced by cyclophosphamide (CTX) treatment. The total WBC count on the 12th day of the CTX-treated group was 3720 cells/mm3 and that of CTX along with Withania was 6120 cells/mm3. Treatment of Withania along with CTX was found to significantly (P < 0.001) increase the bone marrow cellularity (13.1 x 10(6) cells/femur) compared to CTX alone treated group (8 x 10(6) cells/femur). Administration of Withania extract increased the number of alpha-esterase positive cells (1130/4000 cells) in the bone marrow of CTX treated animals, compared to the CTX-alone treated group (687/4000 cells). The major activity of Withania somnifera may be the stimulation of stem cell proliferation. These studies indicate that Withania somnifera could reduce the cyclophosphamide induced toxicity and its usefulness in cancer therapy.

Determination of the novel topoisomerase I inhibitor NU/ICRF 505 and its major metabolite in plasma, tissue and tumour by high-performance liquid chromatography

A high-performance liquid chromatographic technique is presented for the determination of the novel topoisomerase I inhibitor NU/ICRF 505 (a tyrosine conjugate of anthraquinone), its major metabolite (NU/ICRF 505/M) and an internal standard (NU/ICRF 513, dihydroxyphenylalanine conjugate). The method uses a reversed-phase (Apex ODS-2) stationary phase and a mobile phase consisting of 0.25 M ammonium acetate adjusted to pH 3 with 25% (v/v) trifluoroacetic acid and methanol with gradient elution. Between-day variation in retention times were less than 1% for NU/ICRF 505 and 513 and 2.4% for the metabolite. Selective detection was achieved at a wavelength of 545 nm giving a limit of detection of 2 ng on column and 50 ng/ml after sample preparation for all three components. Chromatograms were free from interfering peaks even at very high detector sensitivity. Sample preparation was based on incubation of biological specimens (0.5 ml plasma or homogenate) with dimethylsulphoxide and acetonitrile at 4 degrees C for 30 min followed by centrifugation. Liver and tumour were homogenised in phosphate buffered saline. Recoveries were consistently high (81.7-106.7% for NU/ICRF 505; 88.7-103.3% for NU/ICRF 513 and 83.7-98.7% for NU/ICRF 505/M) with between day coefficients of variation of normally less than 10%. The method will contribute significantly to the preclinical evaluation of NU/ICRF 505.

Detection and separation of the anthrapyrazole CI-941 and its metabolites in serum and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method using ion-pairing chromatography on reversed-phase C18 material with a mobile phase of acetonitrile-water (19:81, v/v) containing 5 mM 1-pentanesulfonic acid was developed for the detection and separation of the anthrapyrazole CI-941 (I) and its metabolites. After sample clean-up with solid-phase extraction, I and its metabolites were measurable at a wavelength of 491 nm. A detection limit of 5 ng/ml was achievable for I. The dicarboxylic acid derivative and the isomers of the monocarboxylic acid derivative could be separated. Application of the method to a human pharmacokinetic study showed two and four metabolites of I in serum and urine respectively.

Influence of renal function on the pharmacokinetics of diacerein after a single oral dose

The pharmacokinetics of diacetylrhein following a single oral dose of 50 mg was studied in 12 healthy volunteers and two groups of 8 patients with mild or severe renal insufficiency. Statistical analysis using a Kruskal-Wallis rank sum test showed a significant difference between the three groups for the following parameters. In severely uraemic patients, median AUC0-infinity was multiplied by a factor of about 2: 40.5 mg.h/l versus 21.3 mg.h/l in healthy subjects, P = 0.04; and t1/2 was prolonged by the same factor: 9.6 h versus 4.3 h in the control group, P = 0.003. Apparent drug availability and renal clearance assessed through urinary data decreased with renal failure, respectively: 14.5% and 0.045 l/h versus 35.4% (P = 0.01) and 0.13 l/h (P = 0.008) in healthy subjects. Amounts of glucuro- and sulpho-conjugates in urine were lower in severely uraemic patients. Intermediate values were observed for mildly uraemic patients. Other parameters: lag time, Cmax, tmax, Vss/F, urinary glucuro- to sulpho-conjugate ratios did not change significantly. Apparent total clearance of rhein was poorly correlated with creatinine clearance and this was related to a decrease of non-renal clearance of rhein in renal insufficiency. It was concluded that, from a pharmacokinetic point of view, a reduction (50%) in the initial dosage of diacerein should be considered in severe renal failure.

Influence of renal function on the pharmacokinetics of diacerein after a single oral dose

The pharmacokinetics of diacerein (a new anti-inflammatory analgesic antipyretic drug) following a single oral dose of 50 mg was studied in 12 healthy volunteers and two groups of eight patients with mild or severe renal insufficiency. Statistical analysis using a Kruskal-Wallis rank sum test showed a significant difference between the three groups for the following parameters. In severely uraemic patients, median AUC0-infinity was multiplied by a factor of ca 2: 40.5 mg h/l versus 21.3 in healthy subjects, P = 0.04; and t1/2 was prolonged by the same factor: 9.6 h versus 4.3 in the control group, P = 0.003. Apparent drug availability and renal clearance assessed through urinary data decreased with renal failure, respectively: 14.5% and 0.045 l/h versus 35.4% (P = 0.01) and 0.13 l/h (P = 0.008) in healthy subjects. Amounts of glucuro and sulfo conjugates in urine were lower in severely uraemic patients. Intermediate values were observed for mildly uraemic patients. Other parameters: lag-time, Cmax, tmax, Vss/F, urinary glucuro- to sulphoconjugate ratios did not change significantly. Apparent total clearance of rhein was poorly correlated with creatinine clearance and this was related to a decrease of non-renal clearance of rhein in renal insufficiency. It was concluded that, from a pharmacokinetic point of view, a reduction (50%) in the maintenance dosage of diacerein should be considered in severe renal failure.

Pharmacokinetics of diacerein in patients with liver cirrhosis

The pharmacokinetics of diacerein following a single oral dose of 50 mg was studied in 12 healthy volunteers, 10 patients with a mild liver cirrhosis (Child Pugh's grade A), and 6 patients with a more severe liver cirrhosis (Child Pugh's grade B to C). Statistical analysis using a Kruskal-Wallis test showed no significant differences between the three groups for the following parameters: median Cmax was 3.9 mg l-1 for the cirrhotic patients group I (CPI) and 3.2 mg l-1 for the cirrhotic patients group II (CPII) versus 3.2 mg l-1 for the healthy volunteers (HV); median t1/2 was 4.9 h for CPI and 4.3 h for CPII versus 4.3 h for HV; median Cl/F was 2.1 l h-1 for CPI and 2.5 l h-1 for CPII versus 1.6 l h-1 for HV; median Vdss/F was 12.6 l for CPI and 14.0 l for CPII versus 13.21 for HV. The urinary parameters were comparable. It was concluded that, from a pharmacokinetic point of view, no reduction in the initial dosage of diacerein need be proposed in liver cirrhosis.

Pharmacokinetics of piroxantrone in a phase I trial of piroxantrone and granulocyte-colony stimulating factor

Piroxantrone is an anthrapyrazole derivative with broad antitumor activity in vitro. In previous phase I trials, the dose-limiting toxicity of this agent was myelosuppression. Therefore, a phase I and pharmacokinetic study of a 1-h infusion of piroxantrone in combination with granulocyte-colony stimulating factor was conducted. In this article, we report the results of the pharmacokinetic analysis. Thirty-seven patients were studied over a dosage range of 150 to 555 mg/m2. The plasma elimination of piroxantrone was biexponential with a mean (+/- SD) t1/2 alpha of 3.2 +/- 2.7 min and a mean (+/- SD) t1/2 beta of 82 +/- 92 min. Clearance was 840 +/- 230 ml/min/m2. A limited sampling strategy was developed to allow the estimation of total drug exposure (area under the plasma concentration-time curve) from the plasma piroxantrone concentrations at 30, 60, and 120 min after the start of the infusion. The pharmacokinetic behavior of a presumed piroxantrone metabolite not previously described in plasma was also characterized. Based on in vitro cytotoxicity studies with partially purified extract of this compound, we do not believe that it contributes to the antitumor effects of piroxantrone at the concentrations observed in plasma. Finally, piroxantrone elimination was linear over the nearly 4-fold dose range studied, indicating that when dose adjustments are made, systemic drug exposure will remain predictable.

High-performance liquid chromatographic analysis of the anticancer drug oxantrazole in rat whole blood and tissues

A reversed-phase high-performance liquid chromatographic (HPLC) assay was developed for the antitumor anthrapyrazole analogue, oxantrazole (OX), in rat whole blood and tissues. Blood samples were mixed with equal volumes of a 25% (w/v) aqueous solution of L-ascorbic acid, whereas tissue samples were homogenized with 1.5-3 volumes of an L-ascorbic acid-methanol-water (1:10:1, w/v/v) mixture to prevent oxidative degradation of OX. Samples were then treated with 60% (v/v) perchloric acid (25-30 microliters/ml of stabilized sample) to precipitate proteins, and centrifuged, with the resultant supernatants analyzed on HPLC utilizing a C8 column. The mobile phase for blood and urine samples consisted of 8% (v/v) glacial acetic acid, 13% (v/v) acetonitrile, 79% (v/v) water, 0.16% (w/v) sodium acetate, and 0.05% (w/v) L-ascorbic acid (final pH 2.7), and was pumped at 1.8 ml/min. Tissue samples were eluted at 2 ml/min with a mobile phase consisting of 8% (v/v) glacial acetic acid, 12% (v/v) acetonitrile, 80% (v/v) water, 0.16% (w/v) sodium acetate, and 0.0;5% (w/v) L-ascorbic acid. OX and internal standard were detected at 514 nm and had retention times of 2.3 and 3.1 min, respectively. The limit of quantitation of OX was 25-50 ng/g. Recovery of OX from biological samples ranged from 50 +/- 0.9% in spleen to 102.8 +/- 1.8% in RG-2 glioma. The analytical method was applied to a pharmacokinetic study in rats.

Prevention of carbon tetrachloride-induced liver necrosis by the chelator alizarin sodium sulfonate

The administration of the calcium chelator alizarin sodium sulfonate (ASR) (100 mg/kg ip in saline) 30 min before or 6 or 10 hr after CCl4 (1 ml/kg ip as a 20% v/v solution in olive oil) partially prevents the necrogenic effect of the hepatotoxin at 24 hr, but prevention of CCl4 fat accumulation was not observed. Protective action cannot be attributed to potential decreasing effects of ASR on CCl4 levels reaching the liver, on the covalent binding of CCl4-reactive metabolites to cellular components, or on CCl4-induced lipid peroxidation because ASR does not modify these parameters significantly. ASR administration increases GSH levels in livers of both control and CCl4-poisoned animals and decreases the calcium content of intoxicated animals at 24 hr of poisoning. ASR significantly lowers the body temperature of CCl4-treated animals at different times of the intoxication process. Present and previous results from our laboratory on the preventive effects of another very specific calcium chelator, calcion, and several anticalmodulins suggest that the beneficial effects of ASR might be associated with its calcium chelating ability. Other protective effects of ASR, such as lowering body temperature or increasing GSH content in liver, cannot be excluded.

Phase I trial of the anthrapyrazole CI-941: prospective evaluation of a pharmacokinetically guided dose-escalation

The development of new drugs in early clinical trials is currently based upon the results of preclinical antitumour and toxicity studies in animals. More recently, the use of preclinical pharmacokinetic information in mice has been proposed to also provide information that might expedite early clinical trials and more specifically phase I studies. The anthrapyrazole CI-941 was one of three chosen for phase I anticancer drug development. In addition, because of the predictability of the preclinical dose limiting toxicity and linear CI-941 pharmacokinetics in mice; a pharmacokinetically guided dose escalation scheme was attempted during the phase I trial, but had to be abandoned. 44 patients were entered who received 95 courses of treatment using a bolus injection every 21 days. The dose range was 5-55 mg/m2. The dose limiting toxicity was leucopenia and other toxicities, which included nausea and vomiting, mucositis, diarrhoea, alopecia and skin discolouration were either mild or manageable. Pharmacokinetic studies were performed with 27 courses. There were wide interpatient variations in the dose-AUC relationship (r = 0.7496) that hampered application of the proposed pharmacokinetically guided dose escalation scheme as planned. No complete or partial responses were observed. The recommended phase II dose using this schedule is 50 mg/m2.

Lack of dose proportional pharmacokinetics for CI-937, an anthrapyrazole DNA intercalator, in mice

The time course of CI-937, an anthrapyrazole DNA intercalator, was studied in plasma of mice after single intravenous doses of 1.2, 8, 12, and 15 mg/kg (1/10 the LD10, 2/3 the LD10, LD10, and LD50). CI-937 concentrations in plasma were determined by a sensitive radioimmunoassay capable of quantifying 0.1 ng/ml. Area under the plasma concentration-time curve increased less than proportionally to dose. Time-averaged plasma clearance was dose-dependent, increasing from 31.1 to 63.6 ml/min/kg over the 1.2 to 12 mg/kg dose range. Terminal half-life in plasma ranged from 11 to 25 days. Fraction plasma protein bound was 69 to 76% from 10 to 10,000 ng/ml, which suggests the nonlinear behavior was not due to saturable protein binding. Potential mechanisms include autoinduction of metabolism and dose-dependent reabsorption from the gastrointestinal tract or kidneys.

Development of a radioimmunoassay for the anthrapyrazole chemotherapy agent CI-937 and the pharmacokinetics of CI-937 in rats

The anthracyclines daunorubicin and doxorubicin are cancer chemotherapy agents that complex DNA and are widely utilized clinically. Cumulative cardiotoxicity, however, limits their prolonged use. The novel anthrapyrazole agent, CI-937, which has shown exceptional in vivo anticancer activity and reduced cardiotoxicity in preclinical models has been developed at the Parke-Davis Pharmaceutical Research Division, Warner-Lambert Co. Due to an inability to extract CI-937 reproducibly from biological fluids, high-performance liquid chromatography is not a feasible analytical method. We developed a radioimmunoassay by conjugating CI-937 to porcine thyroglobulin to elicit rabbit antibody which was used with a radioiodinated derivative. The assay was validated for rat plasma using 50 microliters of sample with a resulting limit of quantitation of 100 pg/ml. By dilution of samples the assay can quantitate CI-937 levels up to 16 micrograms/ml. The antiserum is very specific as evidenced by cross-reactivities of less than 0.4% for structural analogues and less than 0.004% for any of the commonly used cancer chemotherapy agents. Analysis of plasma samples from rats treated with a single 5 mg/kg i.v. dose indicated that CI-937 is rapidly cleared from plasma and is extensively bound to tissues.

Pharmacokinetics of 14C-labelled rhein in rats

After oral or intravenous administration of 14C-rhein to male rats, blood concentrations were measured for up to 48 h. Both mean blood level curves and also the calculated pharmacokinetic constants show a fairly good conformity. Organ distribution was measured up to 2 days after intravenous and up to 7 days after oral application. In most organs the activity is lower than in plasma with very low values in testicles and in brain. Higher values are found in the main excretion organ, the kidney. The plasma protein binding of 14C-rhein is very high both in rat and human serum. Absorption in or adsorption on erythrocytes is very small. Rhein and its metabolites are excreted by kidney and liver. Biliary-excreted rhein metabolites are easily reabsorbed and finally excreted with urine. In bile, there are mainly two conjugated metabolites of rhein, whereas in urine also larger amounts of rhein and one or two additional metabolites can be detected. All metabolites seem to be conjugates, because they can be split by glucuronidase/arylsulfatase to rhein. Rhein is absorbed after oral application by about 50-60% and after administration into the colon by about 50%.

Milk transfer of rhein in the rhesus monkey

A HPLC method was developed to measure rhein, a laxatively active metabolite of sennosides A + B, in milk and plasma. Samples from 2 lactating rhesus monkeys were taken over 48 h after oral administration of sennosides (1 mg kg-1). Detectable rhein levels were found in plasma between 2 and 12 h and in milk between 4 and 12 h after administration, but rhein excretion in milk seems to be far below the dose necessary to elicit a laxative effect in the suckling offspring.

High-performance liquid chromatographic assay for the experimental anticancer agent oxantrazole

Oxantrazole is an anthrapyrazole analogue developed as an anthracycline-like agent with potentially reduced cardiotoxicity. A reversed-phase high-performance liquid chromatographic assay was developed using a C2 column and mobile solvent system of dimethylformamide-acetonitrile-0.2 M ammonium acetate, pH 4.5 (20:5:75, v/v/v) at a flow-rate of 1 ml/min. Drug and internal standard were detected by ultraviolet absorbance at 514 nm. Isolation of drug and internal standard was afforded by elution from C18 disposable isolation columns with a mixture of methanol-glacial acetic acid-0.02 M sodium acetate, pH 4.0 (12:1:3, v/v/v). The assay was linear (r2 greater than 0.99) over concentrations of 0.025-2.5 micrograms/ml and the limit of detection was 10 ng/ml plasma. Oxantrazole was unstable in neutral and particularly alkaline aqueous solutions. Utilizing this assay, plasma pharmacokinetics were determined following intravenous infusion of oxantrazole to beagle dogs. Plasma elimination was rapid with elimination phase half-life values less than 45 min.

Plasma kinetics of mitoxantrone in leukemic patients

The plasma kinetics of mitoxantrone (MX), a new cytostatic anthracenedione, were investigated with HPLC in five leukemic patients suffering from acute myeloid leukemia, at the dose of 24 mg m-2 infused over 30 min at constant rate. The decay of the plasma concentrations was best fitted to a three compartment model with average elimination half-lives of respectively 4.1 min (alpha-phase), 19.8 min (beta-phase) and 8.9 h (gamma-phase), a mean distribution volume of 317 l m-2 and an average total body clearance of 0.37 l min-1 m-2. The cumulative urinary recovery of unchanged MX was 7.5% of the administered dose in 4 days, with the highest elimination during the first day. No MX urinary metabolites or conjugates have been detected.