The oral bioavailability of di-2-ethylhexyl phthalate (DEHP), di-isononyl phthalate (DiNP) and di-(isononyl)-cyclohexane-1,2-dicarboxylate (DINCH®) in house dust.

Phthalates and other plasticizers are detected in high amounts in the indoor environment and therefore house dust can be an exposure source. Especially children have a relatively high unintended uptake of house dust, thus a higher exposure to plasticizers compared to adults may be possible. As accurate as possible exposure assessment data of the oral bioavailability of these compounds are necessary, however only one in vivo study with piglets is available so far. The aim of this study was to examine the oral bioavailability of phthalates and DINCH® in humans, which occur in typical house dust samples. We focused on the high molecular weight phthalates DEHP and DINP and their substitute DINCH®. Eleven volunteers ingested 6 g of house dust sieved to 2 mm. The urine was collected over a period of 36 h. The excreted plasticizers metabolites were quantified by an LC-MS/MS method. The mean recovery of urine metabolites was 51 % ± 20 % for DEHP, 26 % ± 13 % for DINP and 19 % ± 6% for DINCH® based on the parent compounds administered as dust samples. The metabolites of DEHP, DINP and DINCH® reached their maximum concentration after 2-19 hours post dose in urine. The bioavailability of DEHP was in agreement among the different dust samples. For DEHP, we were able to confirm previous findings from the oral bioavailability study with piglets and we could not observe a significant difference between the dust particle size (65 µm vs 2 mm) and the bioavailability. Considering the observed bioavailability, an estimated dust intake of 50 mg/d for toddlers can substantially contribute to the total plasticizer exposure.

Population Pharmacokinetics of Talazoparib in Patients With Advanced Cancer.

Poly(ADP-ribose) polymerase (PARP) inhibitors have been developed to treat cancers associated with somatic BRCA mutations and germline genetic aberrations involved in the DNA damage response. The efficacy, tolerability, and pharmacokinetic/pharmacodynamic (PK/PD) profile of talazoparib, a potent small-molecule PARP inhibitor, was established in 4 clinical studies in cancer patients (2 phase 1 studies PRP-001 and PRP-002, the phase 2 ABRAZO trial, and the phase 3 EMBRACA trial). The current study aimed to describe the population PK of talazoparib and identify covariates that affect talazoparib PK in patients with advanced cancers using pooled data from these 4 studies. Talazoparib PK was well characterized by a 2-compartment model with first-order absorption and absorption lag time. Based on covariate analysis, no dose adjustment for talazoparib is required based on a patient's age, sex, baseline body weight, Asian race, the presence of mild renal or hepatic impairment, or use of acid-reducing agents. A reduced 0.75-mg daily dose is recommended for patients taking a potent P-glycoprotein inhibitor and those with moderate renal impairment. Insufficient data were available to establish dosing recommendations for patients with severe renal and moderate or severe hepatic impairment. The PK of a single 1-mg talazoparib capsule is comparable with 4 0.25-mg capsules. Talazoparib can be taken with or without food. These data provide support for dosing recommendations and labeling information for talazoparib.

Gender effects on rat metabolism of AMG 900, an orally available small molecule aurora kinase inhibitor.

AMG 900 is an orally available small molecule that is highly potent and selective as a pan-aurora kinase inhibitor. AMG 900 is currently undergoing phase 1 clinical evaluation in patients with advanced solid tumors. The metabolism of AMG 900 was investigated in both male and female rats. We conducted studies in bile-duct catheterized (BDC) rats where bile, urine and plasma were analyzed to obtain metabolism profiles for each gender. These studies identified gender differences in the metabolism profiles in bile. Bile contained the majority of the drug related material and contained little unchanged AMG 900 which indicated that metabolism was the prominent process in drug elimination. Although bile contained the same metabolites for both genders, the amount of specific metabolites differed. Male rats metabolized AMG 900 primarily through hydroxylation with subsequent sulfate conjugation on the pyrimidinyl-pyridine side-chain whereas female rats favored a different oxidation site on the thiophene ring's methyl group, which is then metabolized to a carboxylic acid with subsequent conjugation to an acyl glucuronide. CYP phenotyping identified the prominent isoforms as being gender specific or biased in the oxidative metabolism of AMG 900. The metabolism in male rats favored both CYP2C11 and CYP2A2 whereas females favored the CYP2C12. The prominent sulfate conjugate identified in the male rat bile could also be due to male biased metabolism since it has been reported that sulfate conjugation is more prevalent in male rats. All the prominent rat metabolism routes for AMG 900 either have male or female bias. These differences in the rat AMG 900 metabolism profiles in bile can be explained by gender specific P450CYP isoforms.

Characterization of the solubility of a poorly soluble hydroxylated metabolite in human urine and its implications for potential renal toxicity.

The solubility, in human urine, of the major hydroxylated metabolite (M1) of an experimental cognition enhancer was characterized through a series of in vitro experiments in an effort to estimate the probability of crystalluria occurring following oral administration of the parent compound. The aim of these experiments was to determine if a safety margin existed between clinically observed urine concentrations and the solubility of M1. The mean urine concentrations of M1 in young and elderly subjects following oral administration of the parent compound at the highest doses tested, were 4865 +/- 2368 ng/mL and 2764 +/- 791 ng/mL, respectively. In vitro solubility experiments with M1 were conducted in drug-free human urine (37 degrees C) from four male and four female healthy subjects under conditions of high and low urine osmolality. Mean concentrations (n = 16) of M1 in human urine to which solid M1 was added, were 3656 +/- 621 ng/mL, 4678 +/- 1169 ng/mL and 5378 +/- 2474 ng/mL after stirring for 24, 48 and 72 h, respectively, indicating that the ex vivo mean solubility of M1 in human urine is no greater then approximately 5 microg/mL. Addition of solid M1 to urine from human subjects dosed with the parent compound resulted in mean urine M1 concentrations 23.5% greater than those observed in vivo. The results from both experiments indicated a significant overlap between urine concentrations of M1 in vivo following the highest oral administration of the parent drug and M1 solubility measured in vitro, suggesting a high potential for in vivo saturation of urine with M1 with subsequent precipitation, crystalluria, and nephrotoxicity. Consequently, the results of these studies have placed restrictions on the dose that could be administered during clinical development of this compound.

A comparison of quantitative NMR and radiolabelling studies of the metabolism and excretion of Statil (3-(4-bromo-2-fluorobenzyl)-4-oxo-3H-phthalazin-1-ylacetic acid) in the rat.

The identification and quantitation of the metabolites of Statil in rat bile and urine were investigated by 1H- and 19F-NMR spectroscopy and liquid scintillation counting. Male Wistar rats received a single oral dose of 100 mg/kg of radiolabelled Statil. Statil is known to produce glucuronide conjugates which are predominantly excreted into the bile in male rats. The complex multiphasic matrix of bile has been shown to make identification of the resonances by 1H-NMR spectroscopy very difficult as Statil appeared to be micellar bound giving rise to very broad signals. This not only impaired unambiguous signal characterisation but also quantification. The partial separation by SPEC-(1)H-NMR spectroscopy enabled the disruption of the micellar matrices and hence enabled the identification of Statil predominantly as aglycone, and to a lesser extent as glucuronide conjugate. In addition, minor acyl migration products of Statil glucuronide could also be detected as they were separated during the SPEC-process. 19F-NMR spectroscopic measurements on whole bile confirmed their presence as a number of overlapped signals could be observed. The selectivity, simplicity and signal dispersion characteristic of 19F-NMR spectroscopy also enabled the calculation of dose related recoveries of Statil related material in the bile and urine samples without the need for a radiolabel. The aim of this work was to investigate the usefulness and limitations of NMR spectroscopy of intact bile and urine as a means of quantifying levels of drug metabolites. The results obtained from NMR spectroscopy are compared with those obtained using scintillation techniques. Scintillation counting yields unequivocal quantification results, provided the label is preserved in metabolites as has been the case here. In general, quantification by 19F-NMR results similar to those obtained by scintillation counting (in agreement within about 20%). However, discrepancies have been observed with very small and broad 19F-NMR signals in bile. Nevertheless, 19F-NMR spectroscopy of bile is a rapid and facile method for assessing metabolite levels of fluorinated drugs.

Bioavailability, multiple-dose pharmacokinetics, and biotransformation of the aldose reductase inhibitor zopolrestat in dogs.

Zopolrestat (Alond) is a new drug that is being evaluated as an aldose reductase inhibitor for the treatment of diabetic complications. The bioavailability in dogs of a 2 mg/kg oral dose of zopolrestat was 97.2%. In a 1-year, multiple-dose, pharmacokinetic study, systemic exposure increased with increasing dose (50, 100, and 200 mg/kg/day), and there were no consistent changes in exposure with multiple dosing. Renal clearance at 1 year appeared to be higher in males. The magnitude of the potential gender difference in exposure was relatively small and was unlikely to have had a meaningful impact on the pharmacokinetics of zopolrestat in dogs. In studies with bile duct-cannulated dogs, radioactivity from [14C]zopolrestat was primarily eliminated as unchanged drug and acyl glucuronide in the bile and feces (77.3% of the dose) and in urine (18.3% of the dose). The concentrations of acyl glucuronide in urine and feces were approximately 50% of the zopolrestat concentrations. Minor metabolites (each accounting for <1% of the dose) included those resulting from hydroxylation of the phthalazinone ring and glutathione conjugation of the benzothiazole ring.

Pharmacokinetics of the aldose reductase inhibitor, zopolrestat, in humans.

The pharmacokinetics of zopolrestat, an aldose reductase inhibitor that may be useful for the treatment of complications of diabetes, have been investigated using oral doses ranging from 50 to 1200 mg administered to healthy male volunteers. In a single-dose study, Cmax, AUC(0-48), and urinary elimination of zopolrestat increased linearly with increasing dose. The amount of zopolrestat excreted unchanged in the urine within 48 hours ranged from 34 to 45% of the administered dose. Renal clearance ranged from 2.6 to 5.6 mL/min, and appeared to decrease as the dose was increased. In a 2-week multiple dose study, the mean steady-state minimum and maximum plasma concentrations, Cmin and Cmax, were 91.5 and 196 micrograms/mL for subjects administered 800 mg/day, and 131 and 281 micrograms/mL for subjects administered 1200 mg/day. Steady-state AUC(0-24) was also dose proportional. The mean steady state half life of about 30.3 hours was consistent with the observed 2.2-fold accumulation in plasma. Apparent oral clearance (Clpo) was 5.2 mL/min, and apparent volume of distribution (Vdss/F) was 12 L. Mean renal clearance was 2.2 mL/min, and approximately 45% of the administered dose was excreted into the urine at steady state. There was no effect of food consumption during dosing on the extent of absorption of zopolrestat. In in vitro studies, extensive, concentration-dependent binding of zopolrestat to plasma proteins was observed. These data indicate that once-daily dosing of zopolrestat will provide suitable exposure in the treatment of diabetic complications.

Effect of dose on acetylator phenotype distribution of hydralazine.

The effect of dose on acetylator phenotype distribution of hydralazine has been determined, The acetylated metabolites methyltriazolophthalazine (MTP) and 3-hydroxymethyltriazolophthalazine (3-OHMTP) and acid-labile hydralazine (HP) were determined in the 0- to 24-hr urine of patients receiving various doses. The difference between the mean value for the ration 3-OHMTP:HP in the rapid and slow acetylators varied with dose, the greatest difference being after a 200 mg (100 mg twice daily) dose. The distribution of the ratio became less clearly bimodal at lower doses, with overlap between phenotypes occurring at doses of 100 mg (50 mg twice daily) or less. The most effective dose for discriminating between acetylator phenotypes was found to be 200 mg (100 mg twice daily).

Determination of hydralazine metabolites: 4-hydrazino-phthalazin-1-one and n-acetylhydrazinophthalazin-1-one by gas chromatography and s-triazolo[3,4-alpha]phthalazine and phthalazinone by high-performance liquid chromatography.

Methods are described for the determination of 2-N-acetylhydrazinophthalazin-1-one, 4-hydrazinophthalazin-1-one, phthalazinone and s-triazolo[3,4-alpha]phthalazine in human urine. 4-Hydrazinophthalazin-1-one and 4-N-acetylhydrazinophthalazin-1-one (following acid hydrolysis) are reacted with acetylacetone to give a distinctive pyrazole derivative which can be determined by gas chromatography using a nitrogen-specific detector. Phthalazinone and s-triazolo[3,4-alpha]phthalazine are measured underivatised by high-performance liquid chromatography.

Studies in the rabbit on 3-methyltriazolophthalazine, an acetylated metabolite of hydralazine. Evidence for an alternative route of formation.

The formation and disposition of 3-methyltriazolophthalazine (MTP), an acetylated metabolite of hydralazine (H) was studied in rabbits. Following its iv administration MTP was rapidly and almost completely metabolized. The major metabolite in plasma and urine was found to be a hitherto unrecognized glucuronide conjugate, most likely of the carboxylic acid analogue of MTP. The hydralazine-pyruvic acid hydrazone (HPH), which is a major plasma metabolite of H, was recognized as a more potent source for MPT in vivo than was parent H. MTP was also formed in significant amounts in vitro following incubation of HPH in phosphate buffer. We conclude that MTP can arise directly from HPH. Consequently, MTP and the compounds formed during its further biotransformation may not provide any valid measure of the extent to which H is acetylated in vivo.

Isolation and structure determination of a further metabolite of diftalone.

A further metabolite of diftalone, a new antiinflammatory drug, has been identified as 7,14-dihydroxyphthalazino [2,3-b] phthalazine-5,12(7H,14H)-dione, on the basis of physico-chemical properties. The free metabolite was isolated from guinea-pig urine, where it is present as such and as the beta-glucuronide. This structure confirms the selective susceptibility of the methylene group of diftalone towards biological hydroxylation.

3-Hydroxymethyl-s-triazolo[3,4-a]phthalazine, a novel urinary hydralazine metabolite in man.

The elucidation of the structure of a new major metabolic product of hydralazine, 3-hydroxymethyl-s-triazolo[3,4-a]-phthalazine, is described. The structures of several other previously described metabolites of the drug, phthalazone, s-triazolo[3,4-a]phthalazine, and 3-methyl-s-triazolo[3,4-a]phthalazine, are confirmed. A metabolic pathway of hydralazine is also proposed.