RESUMEN
Linezolid (Zyvox), the first of a new class of antibiotics, the oxazolidinones, is approved for treatment of Gram-positive bacterial infections, including resistant strains. The disposition of linezolid in human volunteers was determined, after a 500-mg (100-microCi) oral dose of [(14)C]linezolid. Radioactive linezolid was administered as a single dose, or at steady-state on day 4 of a 10-day, 500-mg b.i.d. regimen of unlabeled linezolid (n = 4/sex/regimen). Mean recovery of radioactivity in excreta was 93.8 +/- 1.1% (range 91.2-95.2%, n = 15), of which 83.9 +/- 3.3% (range 76.7-88.4%) was in urine and 9.9 +/- 3.4% (range 5.3-16.9%) was in feces. There was no major difference in rate or route of excretion of radioactivity by dose regimen. Linezolid was excreted primarily intact, and as two inactive, morpholine ring-oxidized metabolites, PNU-142586 and PNU-142300. Other minor metabolites were characterized by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry and (19)F NMR spectroscopy. After the single radioactive dose, linezolid was the major circulating drug-related material accounting for about 78% (male) and 93% (female) of the radioactivity area under the curve (AUC). PNU-142586 (T(max) of 3-5 h) accounted for about 26% (male) and 9% (female) of the radioactivity AUC. PNU-142300 (T(max) of 2-3 h) accounted for about 7% (male) and 4% (female) of the radioactivity AUC. Overall, mean linezolid and PNU-142586 exposures at steady-state were similar across sex. In conclusion, linezolid circulates in plasma mainly as parent drug. Linezolid and two major, inactive metabolites account for the major portion of linezolid disposition, with urinary excretion representing the major elimination route. Formation of PNU-142586 was the rate-limiting step in the clearance of linezolid.
Asunto(s)
Acetamidas/farmacocinética , Antibacterianos/farmacocinética , Oxazolidinonas/farmacocinética , Acetamidas/sangre , Acetamidas/orina , Adulto , Antibacterianos/sangre , Antibacterianos/orina , Biotransformación , Cromatografía Líquida de Alta Presión , Heces/química , Femenino , Radioisótopos de Flúor , Semivida , Humanos , Marcaje Isotópico , Linezolid , Masculino , Espectrometría de Masas , Persona de Mediana Edad , Oxazolidinonas/sangre , Oxazolidinonas/orina , Espectrofotometría Ultravioleta , Recuento Corporal TotalRESUMEN
Linezolid (PNU-100766) is a new gram-positive oxazolidinone antibiotic that is effective at in vitro concentrations < or =4 microg/ml and in vivo doses < or =10 mg/kg. Because linezolid also competitively inhibits human monoamine oxidase-A (MAO-A; Ki = 55 microM), we monitored its effects on the cardiovascular responses to tyramine and amine cold remedies in comparison with standard MAO inhibitors. In anesthetized rats, the pressor response to 16 microg i.v. tyramine was potentiated by the MAO-A inhibitors clorgyline (0.1-1.0 mg/kg i.v.) and moclobemide (5.0-50 mg/kg p.o.), but not by the MAO-B inhibitor selegiline (0.15-15 mg/kg p.o.). Fifteen milligrams per kilogram intravenous linezolid weakly potentiated i.v. tyramine independent of changes in alpha-adrenoceptor reactivity, but this effect was not enhanced chronically (90-100 mg/kg/day). In conscious rats, 30 mg/kg/day oral linezolid (8 microg/ml plasma concentration) minimally affected the pressor response to 20 mg/kg oral tyramine, whereas 100 mg/kg/day linezolid (20 microg/ml plasma concentration) moderately potentiated this response similar to 3 mg/kg per day moclobemide. Linezolid's tyramine potentiation was reversible, attenuated by food, and independent of pseudoephedrine, phenylpropanolamine, and dextromethorphan interactions. These studies demonstrate that high-dose linezolid only moderately potentiates the cardiovascular effects of tyramine and validate these models for evaluating such MAO inhibitory interactions.
Asunto(s)
Acetamidas/administración & dosificación , Antiinfecciosos/administración & dosificación , Presión Sanguínea/efectos de los fármacos , Inhibidores de la Monoaminooxidasa/farmacología , Oxazolidinonas/administración & dosificación , Simpatomiméticos/farmacología , Tiramina/farmacología , Acetamidas/química , Administración Oral , Animales , Antiinfecciosos/química , Presión Sanguínea/fisiología , Relación Dosis-Respuesta a Droga , Inyecciones Intravenosas , Linezolid , Masculino , Monoaminooxidasa/efectos de los fármacos , Oxazolidinonas/química , Ratas , Ratas Sprague-DawleyRESUMEN
An HPLC-UV method was developed for assay of linezolid in dog, rat, mouse, and rabbit plasma. Linezolid and the internal standard were extracted on a solid phase cartridge (SPE) and separated on a reversed-phase column (C8, 4.6x150 mm, 5 microm) with 20% acetonitrile in water as mobile phase. The SPE quantitatively recovered linezolid and the internal standard from plasma samples. The chromatographic peak height ratio or peak area ratio based on UV absorbency at 251 nm was used for quantitative analysis. The assay procedures were simple and the assay was specific and had adequate precision and accuracy. Calibration standards with concentrations over the range of 0.01 20 microg/ml were validated for routine sample analysis to support the pharmacokinetic and toxicology studies with linezolid in dog, rat, mouse, and rabbit. Analysis of quality control samples showed the coefficients of variation were usually <10% and the measured and theoretical concentrations differed by <10% in most assays. Linezolid in the plasma samples was stable when stored at below -20 degrees C for at least 63 days, at room temperature (22-23 degrees C) for up to 24 h, and after three freeze-thaw cycles. This HPLC method has been successfully used in multiple laboratories to assay plasma samples from pharmacokinetic and toxicology studies with linezolid in the animal species.
Asunto(s)
Acetamidas/sangre , Antiinfecciosos/sangre , Oxazoles/sangre , Oxazolidinonas , Acetamidas/farmacocinética , Animales , Antiinfecciosos/farmacocinética , Calibración , Cromatografía Líquida de Alta Presión , Perros , Indicadores y Reactivos , Linezolid , Ratones , Oxazoles/farmacocinética , Control de Calidad , Conejos , Ratas , Estándares de Referencia , Reproducibilidad de los Resultados , Espectrofotometría UltravioletaRESUMEN
Drugs can fail at any phase during discovery, preclinical or clinical development due to unacceptable levels of toxicity, and liver is commonly the principle target organ. Investigational toxicology methods, using appropriate models and hypotheses, can often resolve problems, identify toxic chemical substituents and salvage therapeutic discovery programs. While in vivo models are used to investigate hepatic drug effects in the context of toxicokinetics and systemic influences, cell culture models provide in vitro systems for investigating specific mechanisms in a precisely controlled environment. Using primary hepatocytes isolated from laboratory animals, we have explored several drug-induced hepatic disorders that surfaced during different phases of drug discovery and development. Additionally, the use of human hepatocytes has allowed us to address concerns for human exposure, examine human relevance of animal data, and provide perspective on problems encountered in clinical trials.
Asunto(s)
Hígado/efectos de los fármacos , Animales , Células Cultivadas , Criopreservación , Humanos , Hígado/citología , Hígado/metabolismo , Oxadiazoles/toxicidad , Quinoxalinas/toxicidad , Espectinomicina/análogos & derivados , Espectinomicina/toxicidadRESUMEN
Thymidine uptake in the organs of the gastrointestinal tract of the rat was studied to determine if cell synthesis was involved in the increases in weight of the stomach, small intestine and colon which result from treatment with 16,16-dimethyl prostaglandin E2 (16,16-dimethyl PGE2). Animals were treated for 2 days with 16,16-dimethyl PGE2. They were injected with the 3H-thymidine, sacrificed and the organs of interest were removed. The total amount of tritium in the stomach, duodenum, jejunum, ileum, and colon was determined. Thymidine uptake was significantly increased in the duodenum (1.50 times), jejunum (1.53 times), and colon (1.40 times) but not in the stomach and ileum. The increases were dose related in the duodenum and jejunum. The colon showed a similar dose response pattern but the changes with dose did not reach significance. These results confirm and extend a previous report that 16,16-dimethyl PGE2 increased thymidine uptake in the duodenum but not the stomach. This is different from gastrin which has been shown by others to increase thymidine uptake in the stomach, duodenum, ileum and colon.
Asunto(s)
16,16-Dimetilprostaglandina E2/farmacología , Sistema Digestivo/metabolismo , Prostaglandinas E Sintéticas/farmacología , Timidina/metabolismo , Animales , Sistema Digestivo/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Femenino , Matemática , Ratas , Factores de TiempoRESUMEN
A gas chromatographic-electron capture (GC-EC) method has been developed for the determination of N-(trans-2-dimethylaminocyclopentyl)-N-(3',4'-dichlorophenyl)pr opanamide, a potential antidepressant drug, and its N-demethyl metabolite in serum. The GC-EC system employed a 3% OV-17 on 100/120 mesh Supelcoport, 2-m X 2-mm i.d. glass column and an isothermal temperature of 195 degrees C. The parent drug and metabolite were extracted from alkalinized serum (pH approximately 13) with toluene, back-extracted into an acidic solution (pH approximately 1), and finally, after adjusting to pH 13, extracted again with toluene. The extensive sample cleanup was necessary to remove serum components which interfered with the analysis. The analytical method was shown to give quantitative recovery of the drug and metabolite, to be linear over a 100-fold concentration range, and to have the necessary precision and sensitivity to detect and quantify as little as 1 ng/mL of the drug or its metabolite. The method has been employed to determine the serum level of drug and metabolite in dogs receiving a single oral dose and to determine the possible correlation between the administered dose and serum levels.
Asunto(s)
Ciclopentanos/sangre , Animales , Cromatografía de Gases/métodos , Perros , Femenino , Concentración de Iones de Hidrógeno , Masculino , Factores de TiempoRESUMEN
The gastric mucosa of animals and man can be damaged by noxious agents and protected by prostaglandins. We developed a Heidenhain pouch dog model which allows the study of multiple doses of the protective or noxious agent. Mucosal damage in the pouch caused by instillation of 160 mM aspirin suspended in 150 mM HCl for two 15-min periods was determined by measuring hemoglobin concentration in isotonic mannitol washes. Hemoglobin levels 24 h after the administration of the acid-aspirin suspension were significantly higher than basal levels. Pretreatment with oral doses of 0.3-3 micrograms/kg 16,16-dimethyl PGE2 at 24 and 18 h and 30 min before the acid-aspirin suspension decreased hemoglobin concentrations in the washes (p less than 0.001).
Asunto(s)
16,16-Dimetilprostaglandina E2/uso terapéutico , Aspirina/toxicidad , Prostaglandinas E Sintéticas/uso terapéutico , Gastropatías/inducido químicamente , Estómago/fisiología , Animales , Aspirina/farmacología , Modelos Animales de Enfermedad , Perros , Femenino , Mucosa Gástrica/efectos de los fármacos , Hemorragia Gastrointestinal/inducido químicamente , Hemorragia Gastrointestinal/prevención & control , Masculino , Gastropatías/prevención & controlRESUMEN
Oral and subcutaneous administration of 16,16-dimethylprostaglandin E2 (16,16-dimethyl PGE2) resulted in an increase in the dry weight of the stomach and small intestine of the female rat. This weight response was rapid, controlled rather than continuously progressing, dose dependent and reversible. The dry weight of the colon also increased but this was not studied in detail. Two-day treatment with 16,16-dimethyl PGE2 caused an increase in the incorporation of 3H-thymidine into the duodenum, jejunum and colon suggesting an increase in cell number. Incorporation into the stomach and ileum was not changed. The number of goblet cells per crypt was increased by prostaglandin treatment in all parts of the small intestine. Since these are mucus producing cells, the small intestine may have increased in cell number and mucus production. Both anti-secretory and cytoprotective doses of 16,16-dimethyl PGE2 caused weight increases in the stomach and small intestine. However, the weight gain by itself was not sufficient to protect the stomach or small intestine from necrotic agents after the prostaglandin was discontinued.
Asunto(s)
16,16-Dimetilprostaglandina E2/farmacología , Sistema Digestivo/efectos de los fármacos , Prostaglandinas E Sintéticas/farmacología , 16,16-Dimetilprostaglandina E2/administración & dosificación , Administración Oral , Animales , Relación Dosis-Respuesta a Droga , Femenino , Inyecciones Subcutáneas , Tamaño de los Órganos/efectos de los fármacos , Ratas , Ratas Endogámicas , Timidina/metabolismo , Factores de TiempoRESUMEN
A population residing in the approximate area of Kalamazoo, MI (latitude north, 42 degrees 17' 29''; longitude west 85 degrees 35' 14''), was examined to determine the influence of seasonal variation on human 25-hydroxyvitamin D3 serum levels. Males and females, ranging in age from 16--64 yr of age and judged normal based on laboratory evaluation and physical examination, participated in the 12-month study. Measurement of 25-hydroxyvitamin D3 serum levels was made by high performance liquid chromatography. A correlation coefficient of 0.776 (P = 0.003) was obtained by comparing average monthly 25-hydroxyvitamin D3 serum levels to average monthly temperatures. A comparison of approximated monthly amounts of sunlight to average monthly 25-hydroxyvitamin D3 serum levels produced a correlation coefficient of 0.747 (p = 0.005). In addition, changes in 25-hydroxyvitamin D3 levels for the population examined fitted a model that demonstrated a relationship to sex and a highly significant periodic relationship to time.
Asunto(s)
Hidroxicolecalciferoles/sangre , Estaciones del Año , Adolescente , Adulto , Femenino , Humanos , Masculino , Persona de Mediana Edad , Factores SexualesRESUMEN
A high-performance liquid chromatographic technique was examined that may allow simultaneous measurement of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in a single sample of human serum. Concentrations of 4 microgram/liter or greater are accurately measured. However, the prepurification procedure allows partial separation of the two metabolites, and so tritiated 25-hydroxyvitamin D3 can be used as an internal standard for accurately monitoring the analytical recovery of 25-hydroxyvitamin D3, but not that of 25-hydroxyvitamin D2. The ability of most prepurification procedures to partly separate the 25-hydroxy metabolites of vitamin D2 and D3 mandates the need for individual internal standards to accurately monitor the recovery of each compound. Values obtained for 25-hydroxyvitamin D2 or composite 25-hydroxyvitamin D when only tritiated 25-hydroxyvitamin D3 is used as a means of monitoring recovery are probably in error.
Asunto(s)
Hidroxicolecalciferoles/sangre , Cromatografía Líquida de Alta Presión/métodos , HumanosRESUMEN
We describe a precise and specific method for measuring 25-hydroxyvitamin D3 in 1 ml of human serum. Extraction with chloroform/methanol followed by chromatography on a 0.5 X 2-cm silica gel column yields a sample that is sufficiently free of extraneous material for high-performance liquid chromatography on a column of microporous silica gel (10 micron average particle diameter). The measurement is not influenced by vitamins D2 or D3, 25-hydroxyvitamin D2, or any of the more hydroxylated metabolites of the vitamin D group. Results by this method correlate well with a competitive protein-binding assay (r = 0.961), but with a negative bias of 6.9 +/- 3.3 microgram/liter. We measured concentrations of 25-hydroxyvitamin D3 in serum drawn during February from 24 persons who were judged normal by physical examinations. The range was 5.5-23.8 microgram/liter (mean, 15.0 +/- 5.2 microgram/liter). The day-to-day CV for the assay was 5.46%.
Asunto(s)
Hidroxicolecalciferoles/sangre , Cromatografía Líquida de Alta Presión/métodos , Humanos , Microquímica , Ensayo de Unión Radioligante/métodosRESUMEN
We describe a radioimmunoassay for measuring clindamycin in serum extracts that is more accurate than the microbiological assay because of the minimal response of the matabolite, N-demethylclindamycin. The assay is not affected by the presence of other antiobiotics. As described it is as sensitive as the microbiological assay, but can be made more sensitive.