Metabolism of patupilone in patients with advanced solid tumor malignancies.

A phase 1, open-label, non-randomized, single center study was conducted to determine the pharmacokinetics, distribution, metabolism, elimination, and mass balance of patupilone in patients with advanced solid tumors. Five patients with advanced solid tumors received 10 mg/m(2) (1.1 MBq) of (14) C-radiolabeled patupilone at cycle 1 as a 20-minute intravenous infusion every 3 weeks until disease progression. Sequential samples of blood/plasma were taken for 3 weeks and urine and fecal samples were collected for seven days after the first dose of patupilone. Patupilone blood levels decreased rapidly after the infusion. The compound showed a large volume of distribution (Vss: 2242 L). The main radiolabeled component in blood was patupilone itself, accompanied by the lactone hydrolysis products that are unlikely to contribute to the pharmacological effect of patupilone. The blood clearance of patupilone was relatively low at 14 L/h. The administered radioactivity dose was excreted slowly (46 % of dose up to 168 h) but ultimately accounted for 91 % of the dose by extrapolation. The fecal excretion of radioactivity was 2-3 times higher than the urinary excretion consistent with hepato-biliary elimination. Three patients had progressive disease and two patients had stable disease as their best response. Patupilone was generally well tolerated in patients with advanced solid tumors with no newly occurring safety events compared to previous clinical studies. In adult solid tumor patients, intravenous radiolabeled patupilone undergoes extensive metabolism with fecal excretion of radioactive metabolites predominating over renal excretion.

Metabolism and disposition of the oral absorption enhancer 14C-radiolabeled 8-(N-2-hydroxy-5-chlorobenzoyl)-amino-caprylic acid (5-CNAC) in healthy postmenopausal women and supplementary investigations in vitro.

8-(N-2-hydroxy-5-chlorobenzoyl)-amino-caprylic acid (5-CNAC), a compound lacking pharmacological activity enhances the absorption of salmon calcitonin, when co-administered. Disposition and biotransformation of 5-CNAC was studied in six healthy postmenopausal women following a single oral dose of 200mg (14)C-radiolabeled 5-CNAC (as disodium monohydrate salt). Blood, plasma, urine and feces collected over 7 days were analyzed for radioactivity. Metabolite profiles were determined in plasma and excreta and metabolite structures were elucidated by LC-MS/MS, LC-(1)H NMR, enzymatic methods and by comparison with reference compounds. Oral 5-CNAC was safe and well tolerated in this study population. 5-CNAC absorption was rapid (t(max)=0.5h; C(max)=9.00 ± 2.74 µM (mean ± SD, n=6) and almost complete. The elimination half-life (t(½)) was 1.5 ± 1.1h. The radioactive dose was excreted mainly in urine (≥ 90%) in form of metabolites and 0.071% as intact 5-CNAC. Excretion of radioactivity in feces was minor and mostly as metabolites (<3%). Radioactivity in plasma reached C(max) (35.4 ± 7.9 µM) at 0.75 h and declined with a half-life of 13.9 ± 4.3h. 5-CNAC accounted for 5.8% of the plasma radioactivity AUC(0-24h). 5-CNAC was rapidly cleared from the systemic circulation, primarily by metabolism. Biotransformation of 5-CNAC involved: (a) stepwise degradation of the octanoic acid side chain and (b) conjugation of 5-CNAC and metabolites with glucuronic acid at the 2-phenolic hydroxyl group. The metabolism of 5-CNAC in vivo could be reproduced in vitro in human hepatocytes. No metabolism of 5-CNAC was observed in human liver microsomes.

Safety and pharmacokinetics of a single 1500-mg dose of famciclovir in adolescents with recurrent herpes labialis.

An open-label study evaluated the safety (n = 53) and pharmacokinetics (n = 8) of single-dose therapy with 1500 mg famciclovir (prodrug of penciclovir) for recurrent herpes labialis in adolescents. Mean Cmax, mean AUC0-∞, and clearance for penciclovir were 9.37 µg/mL, 31.8 µg · h/mL, and 38.2 L/h, respectively, and within the range extrapolated from data in adults. Adverse events were generally mild and transient.

Percutaneous absorption of pimecrolimus is not increased in patients with moderate to severe atopic dermatitis when pimecrolimus cream 1% is applied under occlusion.

AIM: To evaluate the systemic exposure of pimecrolimus cream 1% applied under occlusion in atopic dermatitis (AD) patients. METHODS: A noncomparative, open-label study conducted in 3 groups of moderate to severe AD patients: A (adults, n = 9), B (adolescents, n = 4) and C (children, n = 6). Pimecrolimus cream 1% was applied twice daily for 8.5 days with overnight occlusion in patients with investigator's global assessment scores of ≥3 and AD involving at least 30% of their body surface area. Pimecrolimus blood concentrations were analyzed. RESULTS: The highest pimecrolimus blood concentrations observed in adults, adolescents and children were 1.84, 0.55 and 1.29 ng/ml, respectively. Pimecrolimus blood concentrations and affected body surface area showed no apparent correlation. CONCLUSION: No measurable differences were found in pimecrolimus blood concentrations, efficacy and safety profile when pimecrolimus cream 1% was applied under occlusion versus application without occlusion. These findings reflect the high lipophilic properties of pimecrolimus.

Pharmacokinetics, metabolism, and disposition of deferasirox in beta-thalassemic patients with transfusion-dependent iron overload who are at pharmacokinetic steady state.

Deferasirox (ICL670) is a novel once-daily, orally administered iron chelator to treat chronic iron overload in patients with transfusion-dependent anemias. Absorption, distribution, metabolism, and excretion of [14C]deferasirox at pharmacokinetic steady state was investigated in five adult beta-thalassemic patients. Deferasirox (1000 mg) was given orally once daily for 6 days to achieve steady state. On day 7, patients received a single oral 1000-mg dose (approximately 20 mg/kg) of [14C]deferasirox (2.5 MBq). Blood, plasma, feces, and urine samples collected over 7 days were analyzed for radioactivity, deferasirox, its iron complex Fe-[deferasirox]2, and metabolites. Deferasirox was well absorbed. Deferasirox and its iron complex accounted for 87 and 10%, respectively, of the radioactivity in plasma (area under the curve at steady state). Excretion occurred largely in the feces (84% of dose), and 60% of the radioactivity in the feces was identified as deferasirox. Apparently unchanged deferasirox in feces was partly attributable to incomplete intestinal absorption and partly to hepatobiliary elimination of deferasirox (including first-pass elimination) and of its glucuronide. Renal excretion was only 8% of the dose and included mainly the glucuronide M6. Oxidative metabolism by cytochrome 450 enzymes to M1 [5-hydroxy (OH) deferasirox, presumably by CYP1A] and M4 (5'-OH deferasirox, by CYP2D6) was minor (6 and 2% of the dose, respectively). Direct and indirect evidence indicates that the main pathway of deferasirox metabolism is via glucuronidation to metabolites M3 (acyl glucuronide) and M6 (2-O-glucuronide).

Pharmacokinetics, distribution, metabolism, and excretion of deferasirox and its iron complex in rats.

Deferasirox (Exjade, ICL670, CGP72670) is an iron-chelating drug for p.o. treatment of transfusional iron overload in patients with beta-thalassemia or sickle cell disease. The pharmacokinetics and disposition of deferasirox were investigated in rats. The animals received single intravenous (10 mg/kg) or p.o. (10 or 100 mg/kg) doses of 14C-radiolabeled deferasirox. Biological samples were analyzed for radioactivity (liquid scintillation counting, quantitative whole-body autoradioluminography), for deferasirox and its iron complex [high-performance liquid chromatography (HPLC)/UV], and for metabolites (HPLC with radiodetection, liquid chromatography/mass spectrometry, 1H and 13C NMR, and two-dimensional NMR techniques). At least 75% of p.o.-dosed deferasirox was absorbed. The p.o. bioavailability was 26% at the 10 mg/kg dose and showed an overproportional increase at the 100 mg/kg dose, probably because of saturation of elimination processes. Deferasirox-related radioactivity was distributed mainly to blood, excretory organs, and gastrointestinal tract. Enterohepatic recirculation of deferasirox was observed. No retention occurred in any tissue. The placental barrier was passed to a low extent. Approximately 3% of the dose was transferred into the breast milk. Excretion of deferasirox and metabolites was rapid and complete within 7 days. Key clearance processes were hepatic metabolism and biliary elimination via multidrug resistance protein 2. Deferasirox, iron complex, and metabolites were excreted largely via bile and feces (total > or = 90%). Metabolism included glucuronidation at the carboxylate group (acyl glucuronide M3) and at phenolic hydroxy groups, as well as, to a lower degree, cytochrome P450-catalyzed hydroxylations. Two hydroxylated metabolites (M1 and M2) were administered to rats and were shown not to contribute substantially to iron elimination in vivo.

Pimecrolimus: skin disposition after topical administration in minipigs in vivo and in human skin in vitro.

The dermal disposition of pimecrolimus, a non-steroid, anti-inflammatory calcineurin inhibitor used for the treatment of atopic dermatitis, was evaluated in minipigs in vivo and in human skin in vitro using tritium-radiolabeled compound, and in dermal toxicokinetic investigations in minipigs using unlabeled compound. Following topical application of pimecrolimus 1% market form (MF) cream to minipig skin, approximately 2% of the dose penetrated into the stratum corneum and part of it into deeper skin layers. The remainder of the dose was recovered non-absorbed on the skin surface. The total systemic absorption was or=94% of dose remained non-absorbed, 3.1% was found in the epidermis (including stratum corneum) and 2.9% in the dermis. There was no indication of metabolism of pimecrolimus in human skin in vitro or minipig skin in vivo. No drug accumulation was observed in minipig skin after up to 13 weeks of once daily topical application of 0.1% or 0.3% pimecrolimus cream.

Absorption, distribution, metabolism, and elimination of the direct renin inhibitor aliskiren in healthy volunteers.

Aliskiren (2(S),4(S),5(S),7(S)-N-(2-carbamoyl-2-methylpropyl)-5-amino-4-hydroxy-2,7-diisopropyl-8-[4-methoxy-3-(3-methoxypropoxy)phenyl]-octanamid hemifumarate) is the first in a new class of orally active, nonpeptide direct renin inhibitors developed for the treatment of hypertension. The absorption, distribution, metabolism, and excretion of [(14)C]aliskiren were investigated in four healthy male subjects after administration of a single 300-mg oral dose in an aqueous solution. Plasma radioactivity and aliskiren concentration measurements and complete urine and feces collections were made for 168 h postdose. Peak plasma levels of aliskiren (C(max)) were achieved between 2 and 5 h postdose. Unchanged aliskiren represented the principal circulating species in plasma, accounting for 81% of total plasma radioactivity (AUC(0-infinity)), and indicating very low exposure to metabolites. Terminal half-lives for radioactivity and aliskiren in plasma were 49 h and 44 h, respectively. Dose recovery over 168 h was nearly complete (91.5% of dose); excretion occurred almost completely via the fecal route (90.9%), with only 0.6% recovered in the urine. Unabsorbed drug accounted for a large dose proportion recovered in feces in unchanged form. Based on results from this and from previous studies, the absorbed fraction of aliskiren can be estimated to approximately 5% of dose. The absorbed dose was partly eliminated unchanged via the hepatobiliary route. Oxidized metabolites in excreta accounted for at least 1.3% of the radioactive dose. The major metabolic pathways for aliskiren were O-demethylation at the phenyl-propoxy side chain or 3-methoxy-propoxy group, with further oxidation to the carboxylic acid derivative.

A microplate solid scintillation counter as a radioactivity detector for high performance liquid chromatography in drug metabolism: validation and applications.

Sensitive radioactivity detection following high performance liquid chromatography (HPLC) separation remains a challenge in many drug metabolism studies with radiolabeled compounds. In this work, solid scintillation counting (SSC) after fraction collection into 96-well plates was evaluated as an off-line radioactivity detection method, in comparison with conventional liquid scintillation counting (LSC). The impact of counting time and biological matrix on the quantification of radiolabeled metabolites and parent drug in samples from animal and human absorption, distribution, metabolism and excretion (ADME) studies was investigated. Three different approaches were used to test whether reliable quantification by off-line SSC detection, which requires an approximately constant counting yield during the entire chromatographic run, can be realized: (i) the measurement of radioactivity-spiked biological blank samples without HPLC separation as an extreme case of biological background, (ii) the measurement of radioactivity-spiked HPLC fractions of biological blank samples and (iii) the comparison of radiochromatograms obtained by off-line SSC and LSC of real samples from ADME studies with radiolabeled compounds. Situations in which variations in SSC yield during an HPLC run are likely to lead to significant errors in quantitation were identified and are discussed. However, examples from a number of animal or human ADME studies showed that in the majority of cases off-line SSC provides very similar quantitative data, compared with the reference method of off-line LSC radioactivity detection. Approaches for validation of the off-line SSC approach in critical cases are discussed. The main advantages of off-line SSC, compared with off-line LSC, are lower detection limits and a substantially higher throughput. Several applications of off-line SSC detection in ADME studies are shown.

Metabolism and disposition of vatalanib (PTK787/ZK-222584) in cancer patients.

Vatalanib (PTK787/ZK-222584) is a new oral antiangiogenic molecule that inhibits all known vascular endothelial growth factor receptors. Vatalanib is under investigation for the treatment of solid tumors. Disposition and biotransformation of vatalanib were studied in an open-label, single-center study in patients with advanced cancer. Seven patients were given a single oral (14)C-radiolabeled dose of 1,000 mg of vatalanib administered at steady state, obtained after 14 consecutive daily oral doses of 1,000 mg of nonradiolabeled vatalanib. Plasma, urine, and feces were analyzed for radioactivity, vatalanib, and its metabolites. Metabolite patterns were determined by high-performance liquid chromatography coupled to radioactivity detection with off-line microplate solid scintillation counting and characterized by LC-MS. Vatalanib was well tolerated. The majority of adverse effects corresponded to common toxicity criteria grade 1 or 2. Two patients had stable disease for at least 7 months. Plasma C(max) values of (14)C radioactivity (38.3 +/- 26.0 microM; mean +/- S.D., n = 7) and vatalanib (15.8 +/- 9.5 microM) were reached after 2 and 1.5 h (median), respectively, indicating rapid onset of absorption. Terminal elimination half-lives in plasma were 23.4 +/- 5.5 h for (14)C radioactivity and 4.6 +/- 1.1 h for vatalanib. Vatalanib cleared mainly through oxidative metabolism. Two pharmacologically inactive metabolites, CGP-84368/ZK-260120 [(4-chlorophenyl)-[4-(1-oxy-pyridin-4-yl-methyl)-phthalazin-1-yl]-amine] and NVP-AAW378/ZK-261557 [rac-4-[(4-chloro-phenyl)amino]-alpha-(1-oxido-4-pyridyl)phthalazine-1-methanol], having systemic exposure comparable to that of vatalanib, contributed mainly to the total systemic exposure. Vatalanib and its metabolites were excreted rapidly and mainly via the biliary-fecal route. Excretion of radioactivity was largely complete, with a radiocarbon recovery between 67% and 96% of dose within 7 days (42-74% in feces, 13-29% in urine).

Pimecrolimus: absorption, distribution, metabolism, and excretion in healthy volunteers after a single oral dose and supplementary investigations in vitro.

The absorption and disposition of pimecrolimus, a calcineurin inhibitor developed for the treatment of inflammatory skin diseases, was investigated in four healthy volunteers after a single oral dose of 15 mg of [(3)H]pimecrolimus. Supplementary information was obtained from in vitro experiments. Pimecrolimus was rapidly absorbed. After t(max) (1-3 h), its blood concentrations fell quickly to 3% of C(max) at 24 h, followed by a slow terminal elimination phase (average t(1/2) 62 h). Radioactivity in blood decreased more slowly (8% of C(max) at 24 h). The tissue and blood cell distribution of pimecrolimus was high. The metabolism of pimecrolimus in vivo, which could be well reproduced in vitro (human liver microsomes), was highly complex and involved multiple oxidative O-demethylations and hydroxylations. In blood, pimecrolimus was the major radiolabeled component up to 24 h (49% of radioactivity area under the concentration-time curve(0-24) h), accompanied by a large number of minor metabolites. The average fecal excretion of radioactivity between 0 and 240 h amounted to 78% of dose and represented predominantly a complex mixture of metabolites. In urine, 0 to 240 h, only about 2.5% of the dose and no parent drug was excreted. Hence, pimecrolimus was eliminated almost exclusively by oxidative metabolism. The biotransformation of pimecrolimus was largely catalyzed by CYP3A4/5. Metabolite pools generated in vitro showed low activity in a calcineurin-dependent T-cell activation assay. Hence, metabolites do not seem to contribute significantly to the pharmacological activity of pimecrolimus.

Metabolism and disposition of imatinib mesylate in healthy volunteers.

Imatinib mesylate (GLEEVEC, GLIVEC, formerly STI571) has demonstrated unprecedented efficacy as first-line therapy for treatment for all phases of chronic myelogenous leukemia and metastatic and unresectable malignant gastrointestinal stromal tumors. Disposition and biotransformation of imatinib were studied in four male healthy volunteers after a single oral dose of 239 mg of (14)C-labeled imatinib mesylate. Biological fluids were analyzed for total radioactivity, imatinib, and its main metabolite CGP74588. Metabolite patterns were determined by radio-high-performance liquid chromatography with off-line microplate solid scintillation counting and characterized by liquid chromatography-mass spectrometry. Imatinib treatment was well tolerated without serious adverse events. Absorption was rapid (t(max) 1-2 h) and complete with imatinib as the major radioactive compound in plasma. Maximum plasma concentrations were 0.921 +/- 0.095 mug/ml (mean +/- S.D., n = 4) for imatinib and 0.115 +/- 0.026 mug/ml for the pharmacologically active N-desmethyl metabolite (CGP74588). Mean plasma terminal elimination half-lives were 13.5 +/- 0.9 h for imatinib, 20.6 +/- 1.7 h for CGP74588, and 57.3 +/- 12.5 h for (14)C radioactivity. Imatinib was predominantly cleared through oxidative metabolism. Approximately 65 and 9% of total systemic exposure [AUC(0-24 h) (area under the concentration time curve) of radioactivity] corresponded to imatinib and CGP74588, respectively. The remaining proportion corresponded mainly to oxidized derivatives of imatinib and CGP74588. Imatinib and its metabolites were excreted predominantly via the biliary-fecal route. Excretion of radioactivity was slow with a mean radiocarbon recovery of 80% within 7 days (67% in feces, 13% in urine). Approximately 28 and 13% of the dose in the excreta corresponded to imatinib and CGP74588, respectively.

The pharmacokinetics and pharmacodynamics of zoledronic acid in cancer patients with varying degrees of renal function.

An open-label pharmacokinetic and pharmacodynamic study of zoledronic acid (Zometa) was performed in 19 cancer patients with bone metastases and known, varying levels of renal function. Patients were stratified according to creatinine clearance (CLcr) into different groups of normal (CLcr > 80 mL/min), mildly (CLcr = 50-80 mL/min), or moderately/severely impaired (CLcr = 10-50 mL/min) renal function. Three intravenous infusions of 4 mg zoledronic acid were administered at 1-month intervals between doses. Plasma concentrations and amounts excreted in urine were determined in all subjects, and 4 patients were administered 14C-labeled zoledronic acid to assess excretion and distribution of drug in whole blood. In general, the drug was well tolerated by the patients. Mean area under the plasma concentration versus time curve and mean concentration immediately after cessation of drug infusion were lower, and mean amounts excreted in urine over 24 hours from start of infusion were higher in normal subjects than in those with impaired renal function (36% vs. 28% of excreted dose), although the differences were not significant. Furthermore, with repeated doses, there was no evidence of drug accumulation in plasma or changes in drug exposure in any of the groups, nor was there any evidence of changes in renal function status. Serum levels of markers of bone resorption (serum C-telopeptide and N-telopeptide) were noticeably reduced after each dose of zoledronic acid across all three renal groups. It was concluded that in patients with mildly to moderately reduced renal function, dosage adjustment of zoledronic acid is likely not necessary.