A technique utilizing simultaneous intravenous microdosing of ¹⁴C-labeled drug with oral dosing of non-labeled drug for measurement of absolute bioavailability was evaluated using R-142086 in male dogs. Plasma concentrations of R-142086 were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and those of ¹⁴C-R-142086 were measured by accelerator mass spectrometry (AMS). The absence of metabolites in the plasma and urine was confirmed by a single radioactive peak of the parent compound in the chromatogram after intravenous microdosing of ¹⁴C-R-142086 (1.5 μg/kg). Although plasma concentrations of R-142086 determined by LC-MS/MS were approximately 20% higher than those of ¹⁴C-R-142086 as determined by AMS, there was excellent correlation (r=0.994) between both concentrations after intravenous dosing of ¹⁴C-R-142086 (0.3 mg/kg). The oral bioavailability of R-142086 at 1 mg/kg obtained by simultaneous intravenous microdosing of ¹⁴C-R-142086 was 16.1%, this being slightly higher than the value (12.5%) obtained by separate intravenous dosing of R-142086 (0.3 mg/kg). In conclusion, on utilizing simultaneous intravenous microdosing of ¹⁴C-labeled drug in conjunction with AMS analysis, absolute bioavailability could be approximately measured in dogs, but without total accuracy. Bioavailability in humans may possibly be approximately measured at an earlier stage and at a lower cost.

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  Pairs of forward and reverse primers and TaqMan probes specific to each of 19 drug-metabolizing enzymes (cytochrome P450s, UDP-glucuronosyltransferases, glutathione S-transferases, and sulfotransferases) and 5 transporters (ABC and SLC transporters) in the cynomolgus monkey were prepared. The expression level of each target mRNA was analyzed in total RNA obtained from three specimens of various cynomolgus monkey tissues (adrenal gland, brain, heart, kidney, large intestine, liver, lung, pancreas, prostate, small intestine, spleen, testis, and thymus) by real-time reverse transcription PCR using an Applied Biosystems 7500 Fast Real-Time PCR System. The data obtained in the present study provide useful information on tissue-specific profiles of the expression of these target mRNAs in the cynomolgus monkey, and the results are expected to be valuable in establishing drug metabolism- and transporter-mediated screening systems using the cynomolgus monkey for the evaluation of new chemical entities in new drug development.

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  The objective of this work was to develop a population pharmacokinetic model to assess the influence of subject covariates on the pharmacokinetics of valsartan in children. Data were collected from a single dose study in 26 hypertensive children ages 1 to 16 years. Subjects received 2 mg/kg valsartan suspension up to a maximum dose of 80 mg. Plasma samples were collected and analyzed using LC/MS/MS. Several structural pharmacokinetic models were evaluated for appropriateness. Allometric scaling and standard covariate analyses were performed to explain interindividual variabilities. Objective function values and goodness of fit plots were used for model selection. A posterior predictive check was used for model evaluation. A linear 2-compartment first-order elimination model with zero-order absorption and lag-time best described the disposition of valsartan. Allometric scaling and standard covariate analysis revealed that age and body size have similar influence; however, after adjustment for body size using fat free mass (FFM), the effect of increasing age was no longer significant on valsartan clearance (2% per year relative to a typical 8 year old with FFM of 30 kg). The population pharmacokinetic model reveals that increase in age has minimal influence on body size dependent clearance of valsartan in children.

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  Chimeric mice, constructed by transplanting human hepatocytes, are useful for predicting the human metabolism of drug candidates. In this study, we investigated whether these mice show similar metabolic profile to humans by examining the hydroxylation of S-warfarin reported to be mainly metabolized to S-7-hydroxywarfarin (7-OH-warfarin), catalyzed by CYP2C9, in humans. When S-³H-warfarin was administered to chimeric mice and control (uPA^+/+/SCID^wt/wt) mice, the blood concentration-time curve was higher in chimeric than control mice. Plasma protein binding of S-³H-warfarin of chimeric and control mice amounted to 98.1 and 92.1%, respectively. When S-³H-warfarin was administered to these mice, radioactivity was mainly recovered in urine (81.7% in chimeric mice and 65.9% in control mice). After S-³H-warfarin was administered to these mice, the radioactivity was recovered in the bile of chimeric and control mice at 5.1 and 17.9%, respectively. The main urinary metabolite in chimeric mice was 7-OH-warfarin. the main urinary metabolite in control mice was S-4′-hydroxywarfarin. These results show that mass balance, metabolic disposition of S-³H-warfarin in chimeric mice with humanized liver were similar to reported human data.

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  The human concentrative nucleoside transporter 2 (hCNT2) plays a major role in the intestinal absorption of naturally occurring nucleosides as well as some nucleoside analog drugs. To determine if single nucleotide polymorphisms (SNPs) in the promoter region of hCNT2 affect gene expression, we examined approximately 1 kb upstream the hCNT2 transcription start site. Ninety Chinese samples were screened and seven SNPs were identified: -115T>G, -146T>A, -264A>G, -564G>A, -861A>C, -880T>C and -906C>T. Based on these seven variants and their relative positions, eight haplotypes were identified using PHASE v2.1.1. Three naturally occurring haplotypes were cloned into the pGL3-Basic vector and transfected into HEK293 cells. Dual luciferase assay revealed that haplotype 4 (GTAGACC) and 7 (GAGAACT) exhibited significantly lower expression levels compared to the published haplotype 1 (TTAGATC). Results from our in-vitro study showed that the hCNT2 promoter region haplotype may modulate gene expression and cause different drug responses.

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  Concomitant administration of certain fluoroquinolone antimicrobials and nonsteroidal antiinflammatory agents (NSAIDs) induces serious convulsion in humans. There are differences in convulsive activity among fluoroquinolones and in the potentiation of fluoroquinolone-induced convulsion among NSAIDs, but a comprehensive, quantitative comparison has not been carried out. This study evaluates the inhibitory effects of twelve fluoroquinolones (ciprofloxacin, enoxacin, fleroxacin, gatifloxacin, levofloxacin, lomefloxacin, norfloxacin, ofloxacin, pazufloxacin, prulifloxacin, sparfloxacin, and tosufloxacin) alone or in the presence of an NSAID (4-biphenylacetic acid, diclofenac sodium, loxoprofen, lornoxicam or zaltoprofen) on the GABA_A receptor binding of [³H]muscimol in an in vitro study using mice synaptic plasma membrane. The rank order of inhibitory effects of the fluoroquinolones was prulifloxacin ≈ norfloxacin > ciprofloxacin ≥ enoxacin > gatifloxacin ≥ ofloxacin ≈ tosufloxacin ≈ lomefloxacin > levofloxacin ≥ sparfloxacin ≥ pazufloxacin ≈ fleroxacin. 4-Biphenylacetic acid most potently enhanced the inhibitory effects of the fluoroquinolones, while zaltoprofen, loxoprofen, lornoxicam and diclofenac had essentially no effect. The clinical risk of convulsion for each combination was estimated using a pharmacodynamic model based on receptor occupancy using the in vitro data set obtained and pharmacokinetic parameters in humans collected from the literature. The combinations of 4-biphenylacetic acid with prulifloxacin and enoxacin were concluded to be the most hazardous.

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  We attempted a switch of mammalian target of rapamycin (mTOR) inhibitors from sirolimus to everolimus, a derivative of sirolimus and now on the market in Japan, in two pancreatic islet transplant patients. Both patients were administered tacrolimus with sirolimus or everolimus. They had been administered 5 or 9 mg sirolimus once a day and had maintained a trough concentration of about 15 ng/mL as measured by high performance liquid chromatography with ultraviolet detection. After the switch from sirolimus to everolimus, they were given 10 or 12 mg/day of everolimus twice a day to maintain a trough concentration of 12-15 ng/mL as measured by a fluorescence polarization immunoassay (FPIA) method. Afterward, the blood concentrations of everolimus and sirolimus after the conversion were measured by high performance liquid chromatography with mass spectrometry and everolimus concentrations were found to be 5-10 ng/mL. These data show that a larger dosage is needed for everolimus than sirolimus to maintain the same trough blood concentration. Data obtained by the FPIA for everolimus should be carefully evaluated after switching from sirolimus to everolimus because of the cross-reactivity of the antibody with sirolimus.

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  In this study, the absorption, distribution and excretion of ceramide were examined in rats. After a single oral administration of ³H-ceramide, mean plasma concentration of radioactivity reached maximum at approximately 10.67 hr and decreased with a T_1/2 of 67.12 hr. The mean cumulative excretion of radioactivity in urine and feces accounted for approximately 4.79% and 87.44%, respectively, of the dose. At 96 hr after dosing, 1.67% and 3.67%, respectively, of the dose were still present in the skin and carcass. The radioactivity in the skin at 12 hr was lower than that in plasma and the ratio of skin to plasma concentration was 0.7. However, at 120 hr after dosing, the ratio of skin to plasma concentration increased to 4. A detailed analysis of the distribution of radioactivity in a section of skin showed that radioactivity was located in the dermis and epidermis. At 168 hr, the radioactivity in the epidermis was 8.0% of the radioactivity in skin.
   The results of the present study clearly demonstrate that some ceramide orally administered is distributed gradually in the dermis after gastrointestinal absorption, followed by transfer from the dermis to the epidermis.

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  CYP2C19 is expressed polymorphically with about 21 variant alleles. Genotype-phenotype association studies of CYP2C19 have shown marked deviations, suggesting the presence of other variations in the intronic and 5′ regulatory region affecting its expression. This study aims to identify the genetic polymorphisms and construction of haplotypes of variations in 5′ regulatory region of CYP2C19 among the South Indian population. CYP2C19 5′ regulatory region was amplified and sequenced from the DNA of 58 healthy volunteers of South Indian origin. Genetic analysis revealed the existence of 14 variations including eight novel ones in the 5′ regulatory region. Identified novel variations and their percentage frequencies were: -779A>C (16.4), -828T>A (2.6), -934del>T (3.5), -1051T>C (1.72), -1289T>G (3.4), -1442T>C (12.1), -1498T>G (25.0) and -1558T>G (2.6). The reported variations found in the study population and their frequencies were: -98T>C (28.4), -806C>T (2.6), -833del>T (9.5), 889T>G (10.3), -1041A>G (100.0) and -1418C>T (1.7). The two known non synonymous single nucleotide polymorphisms, 681G>A (^*2 allele) and 636G>A (^*3 allele) were detected at 0.371 and 0.025 frequencies, respectively. Forty three haplotypes were constructed and linkage disequilibrium analysis showed strong linkage between several variations identified in the gene. Fourteen polymorphisms including 8 novel ones in CYP2C19 5′ flanking region are reported for the first time in an Indian population from South India. Results from this study provide additional information for genotyping of CYP2C19 in the South Indian population and probably in the Indian population.

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