Pharmacokinetics and bioavailability of hydromorphone following intravenous and oral administration to human subjects.

In a relatively small pilot study, the half-life of elimination of hydromorphone in six subjects was 2.64 +/- 0.88 hours and the drug had a high volume of distribution, 1.22 l./kg. In addition, the drug was rapidly but incompletely absorbed after oral administration. An equation to predict the plasma concentration of hydromorphone on oral administration was developed from the data of these six subjects.

Plasma levels of clobazam after 10-, 20-, and 40-mg tablet doses in healthy subjects.

It is evident that substantial intersubject and intrasubject varition in the bioavailability of clobazam exists following ingestion of 10, 20 and 40 mg doses in these 12 volunteers. Peak concentrations and area under the plasma level-time curve were directly proportional to the dose of clobazam and the mean plasma half-life of clobazam was about 18 hours regardless of dose administered. The t1/2 value was less than that previously reported, as the current results allow differentiation of parent drug from metabolites. This 18 hr t1/2 compares favorably with the half-life of other benzodiazepines.

Plasma levels of clobazam after three oral dosage forms in health subjects.

As can be seen from the tables, the terminal half-life of clobazam is about 50 hours, and from a solid dosage form the peak plasma level occurs approximately 1.5 hours after ingestion. Thus, there is a significant, yet relatively short, dosage form delay effect when the solid dosage forms are compared to the rapidly available solution of the drug. However, based on the areas under the curve, comparison of the solid dosage forms with the solution indicates that the fraction of clobazam absorbed is 1. Pupil diameter measurement at 2, 4, and 6 hours after ingestion of clobazam correlated well with the plasma levels at these times. Pupils were constricted to the highest degree at 2 hours and approached the initial pupillary diameter at the 6-hour measurement.

Plasma level studies of penbutolol after oral dose in man.

Plasma levels of penbutolol (HOE 893d) were determined in eight healthy adult male subjects after oral administration of 50-mg capsules. Fast absorpiton of the drug from the gastrointestinal tract was indicated by the rapid increase in plasma levels during the absorption phase, with a peak time at about 1 hour after dosing in all subjects. After the peak level, plasma concentrations declined biexponentially, with an average half-life of 2.5 and 27 hours for the fast and slow disposition phases, respectively. These values were in good agreement with data previously found for this drug. Cumulative excretion of intact drug in the urine of the eight subjects during 72 hours after dosing was less than 4 per cent, except for one subject who excreted 9.82 per cent of the dose. Large individual variations were found for area under the plasma level curves, disposition rates, and amounts of intact drug excreted in the urine. Significant pharmacologic effects were noted in all eight subjects at the 50-mg dose level, and mild side effects were evident in one half of these subjects. The average drop in blood pressure and pulse rate for all subjects was 26/18 mm Hg and 19 beats per minute, respectively.

Radioimmunoassay of hydromorphone and hydrocodone in human plasma.

A radioimmunoassay for hydromorphone in human plasma was developed using a commercially available morphine-6-antiserum and tritiated dihydromorphine. In the assay, free and bound drug are separated using dextran-coated charcoal. The method quantitates hydromorphone in the 2.5-20-ng/ml range with minimum sensitivity at 1.0 ng/ml. Within-run precision for hydromorphone as shown by the standard error of the estimate of the linear regression equation is +/- 1.01 ng/ml. Between-run precision data for hydromorphone at the 2,5-, 10-, and 20-ng/ml levels gave percent relative standard deviations of 22.35, 10.96, and 8.55%, respectively. A plasma concentration-time curve from a subject administered a single oral dose of hydromorphone demonstrates the usefulness of the assay in monitoring drug levels in a bioavailability study. The method also is applicable to the analysis of hydrocodone in human plasma in the 10-80-ng/ml range with minimum sensitivity at 3.0 ng/ml. Within-run precision for hydrocodone as shown by the standard error of the estimate of the linear regression equation is +/- 1.06 ng/ml. Between-run precision data at the 15-, 30, and 60-ng/ml levels gave percent relative standard deviations of 12.48, 7.67, and 6.03%, respectively.

Liquid chromatography in pharmaceutical analysis IX: Determination of muscle relaxant--analgesic mixtures using normal phase chromatography.

High-pressure liquid chromatography was used to optimize the resolution of eight widely prescribed therapeutic agents commonly found in muscle relaxant--analgesic mixtures. The compounds were chromatographed on normal phase porpous silica or cyanopropylsilane columns, using various solvent systems paired on the basis of Synder's solvent selectivity scheme to give a polarity index for each system of 3.3. A carisoprodol, phenacetin, and caffeine mixture was selected to demonstrate the utility of the separation and quantification method. The mixture was chromatographed on a porous silica column, using tetrahydrofuran--toluene (50:50) at a flow rate of 2.0 ml/min. Each determination can be achieved in approximately 8 min with an accuracy of 3--5%.

Fluorometric determination of clobazam, a 1,5-benzodiazepine, in human plasma.

A fluorometric procedure for clobazam, a 1,5-benzodiazepine, based on a fluorophore formed upon irradiation of the drug using short wavelength UV light (254 nm) for 35 min is presented. Fluorescence is linear over a 100-6400-ng/ml range using excitation and emission wavelengths of 350 and 400 nm, respectively. Application of the method to the determination of clobazam in spiked human plasma samples revealed that the drug can be determined at nanogram per milliliter levels with an accuracy of 1-5%. The procedure is specific for clobazam in samples containing its major plasma metabolite, N-desmethylclobazam, and also in samples containing 1,4-benzodiazepines and other selected drugs. A plasma level-time profile after oral administration of a single 40-mg dose of clobazam to a healthy adult male is also illustrated.

Liquid chromatography in pharmaceutical analysis XI: determination of muscle relaxant--analgesic mixture using reversed-phase and ion-pair techniques.

High pressure liquid chromatography using reversed-phase and/or ion-pair techniques was used to optimize resolution of aspirin-containing muscle relaxant mixtures as well as other therapeutic agents commonly found in muscle relaxant-analgesic mixtures. The compounds were chromatographed on an octadecylsilane column using methanol--water solvent systems, some of which contained tetrabutylammonium cation as counterion. Mixtures of methocarbamol--aspirin and chlorzoxazone--acetaminophen were selected to demonstrate separation and quantification. The methocarbamol--aspirin mixture was chromatographed with methanol--water (40:60, pH 6.8) containing 0.01 M tetrabutylammonium cation at a flow rate of 2.0 ml/min. The chlorzoxazone--acetaminophen mixture was chromatographed with methanol--water (50:50) at a 2.0 ml/min flow rate. The separation and quantitation of each mixture were achieved in approximately 8 min with accuracy in the 2--3% range.

Liquid chromatography in pharmaceutical analysis X: Determination of chlorzoxazone and hydroxy metabolite in plasma.

A method for the high-pressure liquid chromatographic determination of chlorzoxazone and its hydroxy metabolite in human plasma samples is presented. The separation of the compounds is achieved on an octadecylsilane column with a mobile phase of absolute methanol-distilled water (40:60) at a flow rate of 2.0 ml/min (3100 psig). The chromatographic separation is achieved within 10 min. The overall analysis time is about 45 min, which includes extraction of the drug and metabolite from plasma followed by high-pressure liquid chromatographic separation and quantification. The accuracy of the procedure is in the 1-5% range.

Liquid chromatography in pharmaceutical analysis VII: determination of dantrolene sodium in biological fluids.

Dantrolene sodium can be determined in plasma and urine samples by high-pressure liquid chromatography without interference from its two major metabolites, the hydroxy and acetamido compounds. The minimum detectability of the drug using this procedure is 8 ng. The complete assay including extraction, evaporation, and separation steps can be performed in approximately 70 min with an accuracy of 1--3%.

Liquid chromatography in pharmaceutical analysis VIII: determination of isoniazid and acetyl derivative in plasma and urine samples.

Parameters are described for the qualitative and quantitative analysis of a mixture of isoniazid and its acetyl derivative. The compounds are chromatographed on an octadecylsilane column, using absolute methanol-distilled water (60:40) at pH 2.5 containing 0.01 M dioctyl sodium sulfosuccinate. The flow rate was 2.0 ml/min (2500 psig). The separation and quantification are applicable to plasma and urine samples. The determination in each biological fluid can be achieved in approximately 90 min with percentage accuracies for isoniazid of 5.25 and 7.45 and for the acetyl derivative of 4.47 and 1.56 in plasma and urine, respectively.

Liquid chromatography in pharmaceutical analysis III: separation of diuretic-antihypertensive mixtures.

High-pressure liquid chromatography was used to optimize the resolution of therapeutic agents commonly found in antihypertensive preparations. Seven widely prescribed drugs were investigated. The compounds were chromatographed on reversed-phase octadecyltrichlorosilane (C18) or diphenyldichlorosilane (phenyl) columns, using mixtures of acetonitrile or absolute methanol and distilled water buffered with ammonium acetate, ammonium chloride, or ammonium carbonate. By calculating approximate resolution values, the separation of selected drug mixtures can be predicted.

Liquid chromatography in pharmaceutical analysis IV: determination of antispasmodic mixtures.

Parameters associated with the separation of antianxiety-antispasmodic agents were investigated using high-pressure liquid chromatography. Eight widely prescribed drugs were studied. The compounds were chromatographed on reversed-phase octadecyltrichlorosilane (C18) or diphenyldichlorosilane (phenyl) columns, using mixtures of absolute methanol and distilled water buffered with ammonium dihydrogen phosphate, ammonium acid phosphate, or ammonium carbonate. A mixture of phenobarbital-propantheline bromide was selected to demonstrate the utility of the separation and quantification method. The mixture was chromatographed on a phenyl column, using absolute methanol-aqueous 1 percent ammonium dihydrogen phosphate (60:40) (pH 5.85) at a flow rate of 1.4 ml/min. Each determination can be achieved in approximately 15 min with an accuracy of 1-2 percent.

Liquid chromatography in pharmaceutical analysis VI: determination of dantrolene sodium in a dosage form.

Operating conditions are described for the qualitative and quantitative determination of dantrolene sodium by high-pressure liquid chromatography. A 10-mum porous silica column was employed, using carbon tetrachloride-dimethylformamide (90:10) as the mobile phase. The flow rate was 2.0 ml/min (1800 psig), and the peaks were detected at 375 nm. The analysis of a dosage form can be carried out within 30 min with an accuracy of 3.1%. The results agree favorably with those obtained with a modified spectrophotofluorometric method.

Stable-isotope methodology in the bioavailability study of 17 alpha-methyltestosterone using gas chromatography-mass spectrometry.

The application of a stable-isotope coadministration technique for estimating the relative bioavailability of 17 alpha-methyltestosterone is described. Eight healthy male subjects were administered orally a single 10-mg 17 alpha-methyltestosterone tablet together with a 10-mg 17 alpha-methyltestosterone-d3 solution. The serum concentrations of 17 alpha-methyltestosterone and 17 alpha-methyltestosterone-d3 were determined by gas chromatography-mass spectrometry with selected ion monitoring using 17 alpha-methyltestosterone-d6 as an internal standard. The extent of absorption from the tablet formulation was comparable to that from the oral solution. The stable-isotope methodology was compared with the conventional cross-over method for evaluating the bioavailability of 17 alpha-methyltestosterone.

Examination of blood clobazam levels and several pupillary measures in humans.

The State-Trait Anxiety Inventory was administered to 15 subjects before initiation of the experiment. Three subgroups of five subjects were defined by computing the unweighted sum of the state and trait anxiety scores. A 40-mg dose of clobazam, a 1.5-benzodiazepine, was administered to each subject and repeated with two additional dosage forms following a 2-week washout period. Blood samples were withdrawn, and blood levels were determined by fluorometric analysis. Additionally, pupillary measures of critical flicker fusion, constriction, and dilation in response to a cognitive task were obtained at 0, 2, 4, and 6 hr. A repeated measures analysis of variance revealed that blood levels were, as expected, statistically different over time and dosage form. The pupillary constriction mirrored the blood levels in statistical patterns. The pupillary measure of cognition related to the anxiety state after the performance effects of the cognitive task were statistically removed. The results suggest that clobazam has less immediate human effect than does diazepam.

Liquid chromatography in pharmaceutical analysis V: determination of an isoniazid-pyridoxine hydrochloride mixture.

Operating parameters are described for the qualitative and quantitative analysis of an isoniazid-pyridoxine hydrochloride mixture by high-pressure liquid chromatography. Each compound was chromatographed on an octadecyl column, using absolute methanol-water (60:40) (pH 2.5) containing 0.01 M dioctyl sodium sulfosuccinate. The flow rate was 2.0 ml/min (2500 psig), and the peaks were detected at 293 nm. The analysis was accomplished using ion-pair formation for effecting chromatographic separation. The time required for separation of the drug mixture is approximately 12 min with an accuracy of 1.17-0.30%.

Multivariate analysis of capillary electrophoresis separation conditions for Z-E isomers of clomiphene.

Plackett-Burman (P-B) experimental design has been used to optimize the factors affecting separation of Z and E isomers of clomiphene (zuclomiphene and enclomiphene respectively) using capillary electrophoresis. The P-B design was used to simultaneously investigate the following five factors: buffer ionic strength, buffer pH, heptakis (2,3,6-tri-o-methyl) beta-cyclodextrin (TMCD) concentration, methanol concentration and injection time, each at three levels. In addition to these, a dummy variable was added to estimate the variability of the system. Effects on resolution and analysis time were calculated. Based on the information gained from the P-B design, the following set of conditions was chosen: 100 mM phosphate buffer pH 2.3, 5 mM TMCD, 5% methanol, and 1.7 s hydrodynamic injection time. These conditions gave well-resolved peaks for zuclomiphene and enclomiphene.

Separation of 13-cis and all-trans retinoic acid and their photodegradation products using capillary zone electrophoresis and micellar electrokinetic chromatography (MEC).

Two retinoic acid isomers; 13-cis retinoic acid and all-trans retinoic acid and their photodegradation products were resolved with capillary electrophoresis (CE) (UV detector, 345 nm) using three different mobile phases: method 1--an acetonitrile modified borate buffer (pH 8.5); method 2--borate buffer (pH 8.5) modified with acetonitrile and alpha-cyclodextrin; and method 3--borate buffer (pH 8.5) modified with SDS (MEC). Concentration of acetonitrile in the buffer was varied from 10 to 50% in method 1 and resolutions of 0-1.9 were obtained for the two retinoic acid isomers. Similarly in method 2, concentration of alpha-cyclodextrin in the buffer (with 10% acetonitrile) was varied from 0 to 40 mM, giving resolutions of 0-3.8. In method 3, concentration of SDS in the buffer was varied from 5 to 60 mM resulting in resolutions of 1.3-4.1. Optimum separation conditions for the three methods were applied to the separation of photodegradation products of the two retinoids after exposure to fluorescent light for 36 h. A buffer modified with 45% acetonitrile and the same buffer modified with 10 mM SDS gave incompletely resolved electropherograms with a 72 cm x 50 microns capillary (50 cm to the detector). A buffer containing 20 mM alpha-cyclodextrin 10% acetonitrile gave completely resolved peaks for each isomer. The buffer containing 10 mM SDS gave completely resolved peaks for the photodegradation products when a 122 cm x 50 microns capillary (100 cm to detector) was used.

Normal phase LC-MS determination of retinoic acid degradation products.

The degradation products formed when 13-cis retinoic acid (13-cis RA) and all-trans RA were exposed to fluorescent light and air were investigated. These retinoids are known to undergo Z-E isomerization (due to the existence of four unsaturated double bonds) and oxidation when exposed to light and air. Analysis by LC was carried out on a 25 cm x 4.6 mm Zorbax Rx-SIL (5 microns) with a mobile phase (1.4 ml min-1) of heptane-THF-acetic acid (96.5:3.5:0.015) and an in-line UV (365 nm) detector. The LC eluate was coupled through a Vestec universal interface to a Finnigan 4023 mass spectrometer. EI-mass spectra were obtained at 77 eV from m/z 200 to 350 with multiplier voltage of 1200 V. Solid samples of 13-cis RA and all-trans RA exposed to light and air and also solutions of these retinoids in the mobile phase exposed to the same conditions were used for the analysis. Tentative identities of the degradation products from the mass spectra suggest the isomerization of the retinoids (Z-E isomerism) and the formation of the 5,6-epoxides of these isomers. Identities of the 5,6-epoxides were confirmed with chromatographic and mass spectral data from synthetic samples of the epoxides. Isomerization occurred more readily in solution than in the solid form and the 13-cis RA isomer oxidized more readily than the all-trans isomer.