Lack of effect of tenoxicam on dynamic responses to concurrent oral doses of glucose and glibenclamide.

1. In a single-blind, placebo controlled study the influence of tenoxicam on responses of glucose, insulin and C-peptide to oral doses of glucose and glibenclamide was examined in 16 healthy male volunteers. 2. The subjects received once daily doses of 2.5 mg glibenclamide for 12 days. From day 5 through 12 eight subjects received concomitantly 20 mg tenoxicam once daily and the remaining eight subjects received placebo. 3. On days 1, 4, 5 and 12 glibenclamide was taken with 75 g glucose and blood glucose, serum insulin and C-peptide were measured over 5 h. Plasma levels of glibenclamide and tenoxicam (where appropriate) were followed over 10 h. 4. Characteristic parameters of blood glucose and insulin and C-peptide responses did not change significantly with time (day) and there was no difference between both treatment groups. 5. Baseline insulin increased from 11.7 mu l-1 on day 1 to 15.6 mu l-1 on day 4 (P = 0.009), likewise baseline C-peptide increased from 478 pmol l-1 to 530 pmol l-1 (P = 0.05), but there was no further change in the subsequent treatment period. 6. The AUC of the glibenclamide plasma concentration-time curve did not show changes with time or differences between treatment groups. The mean (s.d.) oral clearance of tenoxicam was 2.5 (1.5) ml min-1 and appeared slightly higher than in previous studies. 7. It was concluded that tenoxicam did not affect overall glycoregulation in healthy subjects under glibenclamide steady state conditions.

Pharmacokinetics of moclobemide after single and multiple oral dosing with 150 milligrams 3 times daily for 15 days.

This study was undertaken to determine the absolute bioavailability and steady-state concentrations of moclobemide after doses of 150 mg. In 14 healthy human volunteers, no differences in tmax, t 1/2 beta, C1/F, Cmax and AUC were found between a single oral dose of 100 mg and one of 150 mg. The mean absolute oral availability was 0.66 and 0.69 respectively. Plasma concentration profiles of moclobemide on repeated dosing with 150 mg 3 times daily for 15 days were essentially superimposable, although the mean concentration was higher than after the single 150 mg dose. This concentration increased over the first week and then remained relatively constant. Mean accumulation factors for moclobemide during the first week were 1.85 for Cmax and 3.0 for AUC. These values were higher than predicted from single-dose characteristics. There was a marked reduction in the variability of AUC and clearance (C1/F) values at steady-state compared with the first dose. Minimum plasma concentrations of the 2 metabolites, Ro 12-5637 and Ro 12-8095, were relatively stable throughout dosing. The exact mechanism of the decrease in systemic and oral clearance of moclobemide with time during multiple oral dosing is not known at present. Either moclobemide inhibits its own clearance or moclobemide metabolism is inhibited by one or more of its metabolites. The findings indicate that, if dosage needs to be adjusted during treatment with moclobemide, the changes should be made carefully and at intervals of not less than 1 week.

Determination of the imidazo quinazoline derivative Ro 13-6438 in biological fluids by high-performance liquid chromatography.

A high-performance liquid chromatographic assay has been developed for the imidazo quinazoline derivative Ro 13-6438 [D-(-)-6-chloro-1,5-dihydro-3-methylimidazo(2,1-b)-quinazolin++ +-2(3H)-one], which is under clinical investigation as a cardioactive drug. The drug is extracted from biological fluids into 1-chlorobutane--1-hexanol (90:10) and back-extracted into perchloric acid. This extract is chromatographed directly, using a reversed-phase high-performance liquid chromatographic system with ultraviolet detection at 254 nm. The detection limit in plasma is about 1 ng ml-1, using a 1-ml sample. The assay is rapid, accurate and sufficiently sensitive for the study of the single-dose kinetics of Ro 13-6438 in man following a 7.5-mg intravenous dose. No instability of the unchanged substance was observed in plasma during storage for one day at room temperature and for five months at --20 degrees C.

Single-dose pharmacokinetics of the MAO-inhibitor moclobemide in man.

The single-dose kinetics of the MAO-inhibitor p-chloro-N-(2-morpholinoethyl)-benzamide (moclobemide, Ro 11-1163) following oral and i.v. administration to six healthy subjects is described. The dosage was 50 mg throughout (1 tablet moclobemide orally, 2.0 ml ampoule moclobemide i.v.). The unchanged drug in plasma was measured by means of an HPLC-assay. The i.v. plasma level curves were analyzed assuming a two-compartment model. The drug was rapidly distributed into the tissue compartment and was then eliminated from the body with a mean half-life t 1/2 beta of about 1 h (range 0.79-1.34 h). The volume of distribution Vss was of medium size (range 0.81-1.25 l/kg). The oral bioavailability was reduced in consequence of the effect of the first passage through the liver and amounted to 44% on average (range 27-70%). As to the drug absorption from the intestinal tract the extent and rate of this process were shown to be large (more than 95% absorbed on average, tmax-values within 1 h).

Sensitive assay for the tricyclic antidepressant Ro 11-2465 in biological fluids by high-performance liquid chromatography and fluorescence detection.

A high-performance liquid chromatographic assay, suitable for pharmacokinetic studies, has been developed for the new tricyclic antidepressant Ro 11-2465, at present under clinical investigation. For concentrations above 0.5 ng/ml, the method involves a simple extraction at basic pH with an organic solvent followed by direct chromatography of this extract on a silica gel column using fluorescence detection. For concentrations below 0.5 ng/ml, an extensive clean-up procedure is required. In both procedures, however, evaporation of the extract and reconstitution of the residue is avoided. The detection limit, using 1 ml of plasma, is about 0.1 ng/ml. This sensitivity is sufficient for following single-dose kinetics of Ro 11-2465 in man.

Determination of bufuralol and its major metabolites in plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of bufuralol, a benzofuran analogue, in plasma is described. The unchanged drug, the major metabolites and an internal standard are extracted from plasma, purified by back-extraction steps and thereafter separated using a reversed-phase liquid chromatographic system. The detection is carried out by means of a fluorescence detector and an UV detector connected in series. The sensitivity of the assay for the unchanged drug and the major metabolite is about 1 ng/ml plasma using a 0.5 ml specimen per analysis and the relative standard deviation of the whole assay lies in the range +/- 4-5%. The procedure was successfully used to determine plasma levels in volunteers following a single oral dose of 40 mg of bufuralol. The results obtained using the new high-performance liquid chromatographic method were compared with those determined by another method which combines gas chromatography with mass fragmentography, and it was found that these two sets of results coincided quite well.

Pharmacokinetic and clinical observations on prolonged administration of flunitrazepam.

Eight patients were given flunitrazepam 2 mg orally, once daily for 28 consecutive days. The time-course of the plasma concentration of unchanged flunitrazepam and its principal metabolites were studied in detail after the first and last doses. Additional blood samples were collected immediately before administration of the tablet on days 4, 7, 11, 14, 18, 21 and 25. Clinically there were not changes during the trial period in the onset of sleep, duration of sleep, depth of sleep measured as number of spontaneous awakenings, or in the patients' condition on awakening. The time-course of the plasma concentration of flunitrazepam could be described by a three-compartment model, assuming that the rate constants remained unchanged during treatment. Maximal plasma concentrations of unchanged flunitrazepam, found two hours after intake, reached 10-15 ng/ml after the first and 15-20 ng/ml after the last dose. The beta-half-life was found to be between 20 and 36 h.

A novel procedure for the determination of tricyclic antidepressants in plasma by use of high performance liquid chromatography.

A novel method for the determination of the antidepressant 3-(1-chloro-5-H-dibenzo [a,d] cycloheptene-5-ylidene)-N,N-dimethylpropylamine-N-oxide hydrochloride and its metabolites by use of high performance liquid chromatography was developed. The procedure is applicable to the assay of other similar drugs in biological samples. The method involves extraction of the unchanged drug and its metabolites from plasma, back-extraction into diluted phosphoric acid and re-extraction into an organic phase. Separation is performed on a silica gel column with an acidic mobile phase, containing sodium dodecyl sulfate as ion-pairing agent. The quantitation is carried out by UV detection. The procedure allows the determination of plasma levels down to about 5 ng/ml of the unchanged drug and its metabolites, respectively, when 1 ml of plasma is used. The plasma levels of two volunteers were determined after a single oral dose of the drug.

A specific and sensitive method for the determination of the anticoagulant phenprocoumon in plasma.

A specific thin-layer chromatographic assay for phenprocoumon has been developed with a sensitivity of 5 ng/ml of plasma, using only 0.2 ml. This sensitivity is more than 20 times higher than that of the published methods. The drug is extracted from acidified plasma, an aliquot of the extract is applied to a silica-gel thin-layer plate and separated from interfering substances. The quantity of phenprocoumon is determined by fluorescence densitometry in situ. The standard deviation of the whole procedure is less than +/- 3%. The new procedure permits pharmacokinetic studies with low doses of phenprocoumon to be performed on volunteers. Furthermore, due to the high sensitivity of the method, it is possible to determine the free drug fraction of this highly protein-bound substance in the plasma of patients. It was shown that, in the therapeutic concentration range, phenprocoumon is bound by about 99.5% to the plasma proteins. Since the assay is simple and quick to perform, a large series of plasma samples can be analysed without any problems.

Determination of amitriptyline and nortriptyline in human plasma by quantitative thin-layer chromatography.

A thin-layer chromatographic method for simultaneous determination of amitriptyline (AT) and nortriptyline (NT) in human plasma is described. Both substances are extracted from biological material by means of a single extraction. The extract is evaporated until dry and the residue quantitatively applied to a silica gel thin-layer plate. AT and NT are separated from interfering plasma components by chromatography. The spots are visualized by nitration, reduction and coupling with N-(1-naphtyl)ethylenediamine on the plate. The intensity of the azo-dyes formed can be measured densitometrically. Using 1 ml of plasma, the sensitivity limit was 0.5 ng/ml for both substances. About 10--15 plasma samples can be analysed per day. The method is applicable to pharmacokinetic studies after a single oral dose of 25 mg AT as hydrochloride in man.

Determination of nanogram amounts of aromatic compounds by spectrophotometry on thin-layer chromatograms.

A highly sensitive method is described for the simultaneous determination of codeine and chlorpheniramine in plasma. Thin-layer chromatography is used for the separation of the drugs. The spots are then rendered visible by nitration of the substances on the thin-layer plate. Codeine can be quantified by direct measurement of the resulting fluorescence. After reduction, the aromatic amines are diazotized and coupled with N-(1-naphthyl)ethylenediamine on the thin-layer plate. For codeine the fluorimetric measurement is more reliable than the colorimetric determination. The sensitivity limits are 8 ng/ml of plasma for codeine phosphate and 1-2 ng/ml of plasma for chlorpheniramine maleate. This procedure is also applicable to other aromatic compounds which can be nitrated by the described method. The method has been applied to compare a determination of the plasma levels of codeine and chlorpheniramine after administration in normal capsules and retard tablets.

Determination of nanogram amounts of primary aromatic amines and nitro compounds in blood and plasma.

A rapid and highly sensitive method, based on the direct fluorimetric scanning of thin-layer chromatograms, is described for the quantitative determination of flunitrazepam and its main metabolites in human blood or plasma. This method is generally applicable to aromatic nitro compounds that are reducible with tin(II) chloride. In particular, it is possible to determine primary amines in nanogram amounts. Fluorescamine is used as a regent to produce fluorescent derivatives. The method is suitable for pharmacokinetic studies of flunitrazepam and its main metabolites in human blood and plasma.