Validated assays for the determination of gemcitabine in human plasma and urine using high-performance liquid chromatography with ultraviolet detection.

Procedures are described for the determination of gemcitabine, a new anti-tumor agent, and its uridine metabolite in human plasma and in human urine. The sample preparation for the plasma assay involves precipitation of plasma proteins with isopropanol and ethyl acetate. Following this, the solids are discarded and the supernatant is evaporated to dryness. For the urine assay, the sample is diluted with methanol and evaporated to dryness. For both procedures, the residue is reconstituted in mobile phase prior to injection into a normal-phase (amino column) liquid chromatographic system followed by UV detection at 272 nm. The limits of quantitation for both compounds are 50 ng/ml in plasma and 20 micrograms/ml in urine. The procedures were used to provide pharmacokinetic data for both compounds in man following the intravenous administration of a 1000 mg/m2 dose of gemcitabine.

Degradation chemistry of gemcitabine hydrochloride, a new antitumor agent.

The anti-tumor agent gemcitabine hydrochloride, a beta-difluoronucleoside, is remarkably stable in the solid state. In 0.1 N HCI solution at 40 degrees C, deamination of gemcitabine occurs, yielding its uridine analogue. Approximately 86% of the initial gemcitabine remains after 4 weeks under these conditions. Cleavage of the N-glycosidic bond of gemcitabine or conversion to its alpha-anomer in 0.1 N HCI solution is not observed over a 4-week period. However, this work has shown that gemcitabine hydrochloride anomerizes in 0.1 N NaOH at 40 degrees C. Approximately 72% of the initial gemcitabine remains after 4 weeks under the basic conditions used. Uridine hydrolysis products are also formed under these conditions. The anormerization reaction, which is unusual under basic conditions, has been confirmed by characterization of the chromatographically isolated alpha-anomer by NMR and mass spectrometry. A mechanism involving an acyclic intermediate is proposed.

Sensitive method for the quantitation of nortriptyline and 10-hydroxynortriptyline in human plasma by capillary gas chromatography with electron-capture detection.

A method for the determination of nortriptyline and 10-hydroxynortriptyline concentrations in human plasma by capillary gas chromatography with electron-capture detection is described. The procedure requires 1.0 ml of plasma and uses maprotiline as an internal standard. The compounds are extracted from alkalinized plasma with hexane-2-butanol (98:2) and back-extracted into hydrochloric acid. The acid solution is then made basic and the compounds are re-extracted into n-butyl chloride. The extract is evaporated to dryness, derivatized with heptafluorobutyric anhydride, and analyzed by gas chromatography on a fused-silica capillary column coated with phenylmethyl silicone. The calibration curves for nortriptyline and 10-hydroxynortriptyline are linear in the ranges 3-40 and 7-90 micrograms/l, respectively, with coefficients of variation for within-day and between-day precision of less than 12%. The quantitation limits for nortriptyline and 10-hydroxynortriptyline are 1 and 3 micrograms/l, respectively. This procedure was used to analyze more than 1400 samples following sub-therapeutic doses of nortriptyline in human subjects. The assay was sufficiently sensitive for use in pharmacokinetic analysis.

Disposition in humans of racemic picenadol, an opioid analgesic.

Racemic picenadol is being tested clinically as an analgesic. The (+)-enantiomer of picenadol is an opioid agonist and the (-)-enantiomer is a weak agonist/antagonist. The disposition of racemic [14C] picenadol was studied in healthy men after a single dose was administered im (N = 3) and orally (N = 5). After the dose, virtually none of the radioactivity that appeared in blood was associated with the red cells. In plasma, approximately 4% of the radioactivity was attributable to the parent drug, the remainder being picenadol glucuronide (approximately 35%) and other metabolites. The t1/2 for total radioactivity was 6 hr, that for the unchanged drug was 3.5 hr. Picenadol was present in plasma almost exclusively as the (+)-enantiomer. However, after incubation with glucuronidase and sulfatase, plasma contained 2 to 4 times more (-)- than (+)-picenadol, indicating that more conjugated (-)-picenadol than conjugated (+)-picenadol was in the plasma. After im and oral administration of [14C]picenadol, plasma levels of radioactivity were generally 10 and 70 times higher than those in saliva, respectively. More than 90% of the administered radioactivity was excreted in the urine, mostly as picendol glucuronide, and lesser amounts of picenadol sulfate and N-desmethylpicenadol sulfate. Only about 1% of the administered dose of picenadol appeared unchanged in urine. The disposition of racemic picenadol in humans was stereoselective, the (-)-picenadol apparently being metabolized preferentially over the (+)-enantiomer. This finding was of particular interest in view of the dissimilar pharmacologic activities of the enantiomers.(ABSTRACT TRUNCATED AT 250 WORDS)