Lichenoid drug eruption to salsalate

Cutaneous lichenoid eruptions can arise as a result of exogenous compound exposures. Pharmaceutical drugs, industrial compounds, and inhaled particles have been implicated as causative agents. To date, there have been no recorded cases of lichenoid drug eruptions (LDEs) caused by clinical use of the nonsteroidal anti-inflammatory drug salsalate. We describe a patient who experienced a lichenoid eruption after the initiation of salsalate for relief of arthritic pain. This eruption emerged after 1 month of therapy with salsalate, persisted for as long as salsalate was administered, and cleared within 3 weeks of discontinuing the medication. LDEs can clinically and histologically resemble idiopathic or classic lichen planus. Integrating drug history, clinical morphology, clinical distribution, and histopathology can aid in the differentiation. As in our patient's case, curative treatment for LDE requires discontinuation of the drug.

Increased throughput in quantitative bioanalysis using parallel-column liquid chromatography with mass spectrometric detection

The feasibility of quantitative bioanalysis by parallel-column liquid chromatography in conjunction with a conventional single-source electrospray mass spectrometer has been investigated using plasma samples containing a drug and its three metabolites. Within a single chromatographic run time, sample injections were made alternately onto each of two analytical columns in parallel at specified intervals, with a mass spectrometer data file opened at every injection. Thus, the mass spectrometer collected data from two sample injections into separate data files within a single chromatographic run time. Therefore, without sacrificing the chromatographic separation or the selected reaction monitoring (SRM) dwell time, the sample throughput was increased by a factor of two. Comparing the method validation results obtained using the two-column system with those obtained using the corresponding conventional single-column approach, the methods on the two systems were found to be equivalent in terms of accuracy and precision. The parallel-column system is simple and can be implemented using existing laboratory equipment with no additional capital outlays. A parallel-column system configured in this manner can be used not only for the within-a-run analysis of two samples containing two different sets of chemical entities, but also for the within-a-run analysis of two samples containing the same set of chemical entities.

An automated method of sample preparation of biofluids using pierceable caps to eliminate the uncapping of the sample tubes during sample transfer

Biological samples are normally collected and stored frozen in capped tubes until analysis. To obtain aliquots of biological samples for analysis, the sample tubes have to be thawed, uncapped, samples removed and then recapped for further storage. In this paper, we report an automated method of sample transfer devised to eliminate the uncapping and recapping process. This sampling method was incorporated into an automated liquid-liquid extraction procedure of plasma samples. Using a robotic system, the plasma samples were transferred directly from pierceable capped tubes into microtubes contained in a 96-position block. The aliquoted samples were extracted with methyl-tert-butyl ether in the same microtubes. The supernatant organic layers were transferred to a 96-well collection plate and evaporated to dryness. The dried extracts were reconstituted and injected from the same plate for analysis by liquid chromatography with tandem mass spectrometry.

Direct-injection LC-MS-MS method for high-throughput simultaneous quantitation of simvastatin and simvastatin acid in human plasma

A direct-injection liquid chromatography-mass spectrometry-mass spectrometry (LC-MS-MS) method was developed and validated for the simultaneous quantitation in human plasma of the widely used cholesterol-lowering prodrug simvastatin and its in vivo generated active drug, simvastatin acid. The plasma samples were injected into the LC-MS-MS system after simply adding the internal standard solution in an aqueous buffer and centrifuging. The analytes in the buffered plasma samples were found to be stable for at least 24 h at 4 degrees C. The method was successfully validated under the challenging condition of using a large number of quality control (QC) samples including those in which the ratio of the simvastatin concentration to the simvastatin acid concentration was different from the concentration ratio in the calibration curve standards. Under the dual stabilizing conditions of lower temperature (4 degrees C) and lower plasma pH of 4.9, the in-process hydrolysis of simvastatin to simvastatin acid or the lactonization of simvastatin acid to simvastatin was minimized to < or = 1.0%. Although the entire run time for on-line cleanup and analysis was only 2.5 min, chromatographic base-line separation of simvastatin from simvastatin acid, which was required to avoid the interference by simvastatin acid with the simvastatin selected reaction monitoring channel, was achieved. The desired lower limit of quantitation of 0.5 ng/ml was achieved by injecting only an equivalent of 8.0 microl of the plasma sample. The extraction column lasted for at least 500 injections.

Ternary-column system for high-throughput direct-injection bioanalysis by liquid chromatography/tandem mass spectrometry

As a continuation of our efforts to improve our high-flow on-line bioanalytical approach for high-throughput quantitation of drugs and metabolites in biological matrices by high-performance liquid chromatography (LC) and tandem mass spectrometry (MS/MS), we have developed a ternary-column on-line LC/MS/MS system with dual extraction columns used in parallel for purification and an analytical column for analysis. The advantage of the dual extraction column system is that sample analysis can take place in one of the extraction columns while the other column is being equilibrated. Thus, the equilibration time does not add to the run time, hence shortening the injection cycle time and increasing the sample throughput. Moreover, the use of two extraction columns in parallel increases the number of samples that can be injected before the system fails due to an overused extraction column. Such a system has successfully been used to develop and validate a positive ion electrospray LC/MS/MS bioanalytical method for the quantitative determination of a guanidine-containing drug candidate in rat plasma. The system used for this work utilized two Oasis HLB extraction columns (1 x 50 mm, 30 microm), one C18 analytical column (3.9 x 50 mm, 5 microm), a ten-port switching value and a tandem mass spectrometer. The on-line analysis was accomplished by the direct injection of 10 microL of the sample, obtained by mixing a rat plasma sample 1:1 with an aqueous internal standard solution. Selected reaction monitoring (SRM) was utilized for the detection of the analyte and internal standard. The standard curve range was 1.00-200 ng/mL. The intra- and inter-day precision and accuracy were within 6.6%. The on-line purification step lasted for only 0.3 min and total run time was only 1.6 min.

Direct injection versus liquid-liquid extraction for plasma sample analysis by high performance liquid chromatography with tandem mass spectrometry

Direct injection versus liquid-liquid extraction for post-dose human plasma sample analysis by high performance liquid chromatography with tandem mass spectrometry (LC/MS/MS) have been studied using a drug candidate compound. For the direct-injection method, an Oasis(R) HLB column (1 x 50 mm, 30 micrometer) was used as the on-line extraction column and a conventional Waters symmetry C18 column (3.9 x 50 mm, 5 micrometer) was used as the analytical column. Each plasma sample (100 microL) was mixed with 100 microL of a working solution of the internal standard in aqueous 0.05 M ammonium acetate (pH 6.9), and portions (10 microL) of these samples were then injected into the LC/MS/MS system. For the liquid-liquid extraction method, a YMC Basic C18 column (2.0 x 50 mm, 5 micrometer) was used as the analytical column. Each sample (0.5 mL) was extracted with methyl tert-butyl ether and the extract was reconstituted and injected into the LC/MS/MS system. The total analysis time for both methods was 2.0 min per sample. The accuracy, inter-day precision and intra-day precision obtained from the quality control samples were within 8% for both methods. The analysis results of post-dose human plasma samples showed that the deviations of 91% of the concentrations obtained using the direct-injection method were within +/-20% from the concentrations obtained using the liquid-liquid extraction method, and the overall average percentage deviation was -1.5%. The results showed that the two methods were equivalent in terms of total chromatographic run time, accuracy and precision. However, for a batch of 100 samples, the sample preparation time for the direct-injection method was only about 25% of the time required for liquid-liquid extraction. This decrease in sample preparation time resulted in the doubling of the overall sample analysis throughput.

A versatile system of high-flow high performance liquid chromatography with tandem mass spectrometry for rapid direct-injection analysis of plasma samples for quantitation of a beta-lactam drug candidate and its open-ring biotransformation product

A bioanalytical method has been developed and validated for quantitation of a beta-lactam drug candidate and its open-ring biotransformation product utilizing high-flow high-performance liquid chromatography (HPLC) for on-line purification of plasma samples and electrospray tandem mass spectrometry for detection and quantitation. The HPLC system used two columns: an Oasis column (1 x 50 mm, 30 microm) as the on-line extraction column and a conventional C18 column (2 x 50 mm, 5 microm) as the analytical column. Each plasma standard or quality control (QC) sample (50 microL) was mixed with 50 microL of a working solution of the internal standard in aqueous 0.5 M ammonium acetate (pH 4.0). Portions (10 microL) of these samples were then injected into an Oasis column with a mobile phase consisting of 100% aqueous 1 mM formic acid at a high flow rate (4.0 mL/min), with the effluent from the Oasis column directed to waste and not to the mass spectrometer. After the purification step, the Oasis column effluent was directed to the analytical column and the mass spectrometer and the analytes were eluted with methanol/aqueous 1 mM formic acid (70:30) at a flow rate of 1.0 mL/min. The total analysis time was 1.6 min per sample. The standard curve range was 0.980 to 250 ng/mL. The accuracy, inter-day precision and intra-day precision were within 10% for both compounds.

Quantitative analytical methods for the determination of a new hypertension drug, CGS 25462, and its metabolites (CGS 25659 and CGS 24592) in human plasma by high-performance liquid chromatography

Two simple and sensitive reversed-phase high-performance liquid chromatography (HPLC) methods were developed and validated for the quantitative determination of a novel hypertension drug CGS 25462 and its major metabolites CGS 24592 and CGS 25659 in human plasma. CGS 25462 and CGS 25798 (internal standard) were purified by one-step liquid-liquid extraction with methylene chloride. The metabolites were analyzed on HPLC after plasma protein precipitation with 10% trichloroacetic acid (TCA). Separations were achieved on a Zorbax RX C18 column. All compounds were detected by using a fluorescence detector. The excitation wavelength was 254 nm, and emission was monitored at 325+/-12.5 nm. Assessment of recovery and reproducibility indicated good accuracy and precision. Over the validation concentration range of 10 to 1000 ng/ml for CGS 25462 and 25 to 5000 ng/ml for both metabolites, overall mean relative recoveries were 96% for CGS 25462, 101% for CGS 25659 and 107% for CGS 24592, and the coefficients of variation were 4.6 to 13% for CGS 25462, 9.5 to 13% for CGS 25659 and 7.7 to 15% for CGS 24592. The limits of quantification (LOQs) were 10 ng/ml for CGS 25462 and 25 ng/ml for CGS 24592 and CGS 25659, which were of sufficient sensitivity to measure the concentrations of CGS 25462, CGS 25659 and CGS 24592 in plasma samples from normal volunteers following a single 800 mg oral dose.

Enantioselective determination of selfotel in human urine by high-performance liquid chromatography on a chiral stationary phase after derivatization with 9-fluorenylmethyl chloroformate

An analytical method for the enantioselective determination of selfotel in human urine has been developed and validated. The method is based on high-performance liquid chromatography and utilizes CGS 20005 (a selfotel analog) as the internal standard. Urine samples were derivatized in situ with o-phthalic dicarboxaldehyde-3-mercaptopropionic acid and 9-fluorenylmethyl chloroformate (FMOC). Chromatographic separations of the FMOC derivatives of selfotel enantiomers and the internal standard were achieved using a column switching system consisting of an Inertsil ODS-2 column (75x4.6 mm I.D., 5 microm) and a Chiralcel OD-R column (250x4.6 mm I.D., 10 microm). The composition of the mobile phase was acetonitrile-0.1 M phosphate buffer, pH 2.50 (35:65) for the Inertsil ODS-2 column and acetonitrile-0.1 M phosphate buffer, pH 2.00 (35:65) for the Chiralcel OD-R column. The analytes were monitored using fluorescence detection at an excitation wavelength of 262 nm and an emission wavelength of 314 nm. The limit of quantification (LOQ) for this method is 0.25 microg/ml for each selfotel enantiomer. The method was successfully utilized to determine preliminary selfotel stereospecific pharmacokinetics.

Explaining variable absorption of a hypolipidemic agent (CGP 43371) in healthy subjects by gamma scintigraphy and pharmacokinetics

The gastrointestinal absorption of a hypolipidemic agent (CGP 43371) was investigated using an external scintigraphy technique in six healthy men. After an overnight fast, subjects received a single 800-mg oral dose of CGP 43371 (4 capsules of 200 mg each) and one capsule of radioactive samarium-153 oxide (100-130 microCi) as a nonabsorbable marker of gastrointestinal transit and fecal recovery for CGP 43371. In vivo gastrointestinal transit of samarium-153 was monitored via gamma scintigraphy for 48 hours after administration to coincide with blood sampling. Samarium-153 content in whole fecal samples was determined by external gamma scintigraphy, and CGP 43371 content in both fecal and plasma samples was determined using high-performance liquid chromatography (HPLC). The results of fecal analysis indicated that transit of the two compounds in the gastrointestinal tract were similar, and bioavailability of CGP 43371 was calculated to be 9% based on the difference between the cumulative amounts of the nonabsorbable radioactive marker and CGP 43371 found in the feces. The onset of drug absorption occurred 4 hours after administration when radioactive samarium-153 was in the distal small bowel, and peak plasma drug level occurred 6 hours after administration, which corresponded with the arrival of samarium-153 in the terminal ileum and ileal/cecal junction. This observation supported the concept that primary absorption of this compound was in the distal to terminal portion of the ileum. Although the onset of drug absorption was delayed, it was curious that the rate of gastric emptying also affected the extent of absorption. A positive correlation (r = 0.91) between area under the drug curve (AUC) and area under the transit curve (AUTC) of the gastric emptying showed that longer gastric residence improved oral absorption of CGP 43371.

Quantitative determination and pharmacokinetics of a new antipsychotic (CGS 13429A) in human plasma using capillary gas chromatography/mass spectrometry

A quantitative analytical method is described for the determination of a new antipsychotic (CGS 13429A) in human plasma. The method relies on capillary gas chromatography/mass spectrometry in the positive chemical ionization mode, utilizing ammonia reagent gas. The limit of quantification (LOQ) was 0.1 ng ml-1 and the method was validated over a concentration range of 0.1-50 ng ml-1. The method was used to measure CGS 13429A plasma concentrations following the administration of single oral ascending doses ranging from 0.1 to 10 mg in healthy male volunteers. The drug was rapidly absorbed (Tmax ranged from 1.1 to 3.7 h) and showed a mean terminal elimination half-life of 8.1 h, which was independent of dose. Area-under-the-curve (AUC) along with Cmax values were proportional to the administered dose.

A quantitative analytical method for the determination of a new anxiolytic (CGS 19480A) in human plasma using high performance liquid chromatography

A sensitive and specific analytical method has been developed for the determination of a new anxiolytic (CGS 19480A) in human plasma using high performance liquid chromatography (HPLC). The drug and internal standard (CGS 18102A), were extracted with hexane at pH 7. Separations were achieved by reversed phase chromatography on a Nucleosil 5 C18 column at a flow rate of 1.0 mL/min. The mobile phase consisted of acetonitrile: 0.01 M phosphate buffer (pH 7): methanol (51:35:14, v:v:v), where the final pH of the mobile phase was adjusted to 4.0 using 85% phosphoric acid. Plasma standard curves were linear from 5.0 to 500 ng/ml, with recovery of the drug being greater than 95% at all concentrations. The method was validated over a concentration range of 5.0 to 500 ng/mL with a limit of quantification of 5.0 ng/mL. The method was successfully applied to the analysis of clinical samples from a single-dose safety and tolerability study conducted in six healthy male volunteers.

Determination of the rifamycin-related hypolipidemic drug CGP 43371 in human feces, plasma and urine by high-performance liquid chromatography

A simple, rapid and sensitive normal-phase high-performance liquid chromatographic (HPLC) method was developed and validated for the determination of a novel hypolipidemic agent in human feces, plasma and urine. This experimental drug candidate is structurally related to rifamycin. The compound and internal standard were isolated from biological matrices by a one step liquid-liquid extraction. Separations were achieved on a mu Porasil silica gel column. Recovery and reproducibility assessments indicated good accuracy and precision. The overall mean relative recoveries were 93.3% from feces (0.2-20 micrograms/mg), 95.1% from plasma (20-500 ng/ml) and 97.5% from urine (20-500 ng/ml), with coefficients of variation ranging from 0.7 to 10.0% for feces, 3.0 to 12.7% for plasma and 2.3 to 10.6% for urine. The limits of quantification were 0.2 micrograms/mg for feces and 20 ng/ml for plasma and urine. The method has sufficient sensitivity to support clinical trials, and was utilized to measure concentrations of the compound in fecal, plasma and urine samples from healthy male volunteers who had received a single 800-mg oral dose.

Quantitative determination of the NMDA antagonist cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755) in human plasma using capillary gas chromatography/mass spectrometry

An analytical method has been developed and validated for the quantitative determination of the N-methyl-D-aspartate (NMDA) antagonist cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755) in human plasma. It is a member of a new class of compounds with the potential to be neuroprotective and attenuate neuronal damage resulting from brain trauma caused by stroke and head trauma. The method is based on gas chromatography/mass spectrometry and uses stable-isotope labeled CGS 19755 as the internal standard. Samples (1 ml) were first acidified (pH 2), then extracted using a solid-phase aminopropyl ion exchange column. The drug was eluted with NH4OH and evaporated until dry. Extracts were derivatized with a mixture of pentafluoropropionic anhydride and pentafluoropropanol, and analyzed by gas chromatography/mass spectrometry. Separation was accomplished on a DB-225 capillary column (15 m x 0.32 mm) with a 0.25 micron film thickness. Mass spectrometry was carried out under negative ion ammonia chemical ionization conditions with selected ion monitoring at m/z 760 and 764 for derivatized CGS 19755 and the internal standard, respectively. Specificity was shown by the lack of interfering peaks at the retention time of CGS 19755 and internal standard. Recovery and reproducibility assessments show good accuracy, precision and linearity over the validated concentration range of 2-5000 ng ml-1.

A quantitative analytical method for the determination of a new thromboxane synthetase inhibitor (CGS 22652) in human plasma using high performance liquid chromatography

A quantitative analytical method for the determination of a new thromboxane synthetase inhibitor (CGS 22652) in human plasma has been developed using high performance liquid chromatography (HPLC). The drug and internal standard (CGS 23298) were extracted with methylene chloride at pH 4.8. Separations were achieved by reversed phase chromatography using a mobile phase consisting of acetonitrile: 0.01M citrate/phosphate buffer (pH 3.5): methanol:tetrahydrofuran (45:45:9:1, v/v/v/v), on a 5 microns C18 column at a flow rate of 1.0 mL/min. Plasma standard curves were linear from 50 to 2000 ng/mL, with recovery of the drug being greater than 94% at all concentrations. The method was validated over a concentration range of 50 to 2000 ng/mL, with a limit of quantification of 50 ng/mL. The method was successfully applied to the analysis of clinical samples from a single-dose safety and tolerability study conducted in healthy male volunteers.

Perceived gender roles of managers and effective conflict management

This study examined the perceived conflict-management behavior and effectiveness of 45 managers who had been rated by 230 subordinates as representing masculine, feminine, or androgynous gender-role types. Analysis indicated that managers perceived by their subordinates as being androgynous were rated as better handlers of conflict situations than their masculine or feminine peers.

The metabolism of CGS—15873 in man using stable isotope pattern recognition techniques

CGS 15873 is a relatively specific dopamine agonist with preferential activity at the presynaptic autoreceptor and therefore may represent a novel agent for the treatment of schizophrenia and/or Parkinson's disease. Several metabolites have been identified in the rat and monkey using an isotopically enriched dosing solution and pattern recognition techniques coupled with GC/MS and LC/MS. In this study, the metabolism of CGS 15873 was investigated in man using these same techniques. In urine, specific isotope clusters were found that matched the dosing solution pattern. Three metabolites were identified: an O-glucuronide conjugate of the parent drug, N-despropyl CGS 15873, and a keto metabolite of CGS 15873. Thermospray LC/MS allowed for the direct confirmation of the conjugated metabolite. GC/MS required derivatization but afforded greater sensitivity compared to LC/MS.

An automated method for the determination of a new potential antiepileptic agent (CGP 33101) in human plasma using high performance liquid chromatography

An automated analytical method utilizing laboratory robotics has been developed and validated for quantifying concentrations of a new antiepileptic drug candidate (CGP 33101) in human plasma. The robotic system aliquots the biological sample, adds the internal standard (CGP 23901) and pH 12 buffer, extracts the compounds from the basified matrix into an organic phase (methyl-t-butyl ether:dichloromethane, 2:1) and concentrates the extracts for reversed-phase, high performance liquid chromatographic (HPLC) analysis. The robotic system is directly interfaced with the HPLC system. Separation is achieved on a Hypersil 3 microns C18 column (4.6 x 50 mm) with ultraviolet detection of the analytes at 230 nm. Specificity was demonstrated by the lack of interfering peaks at the retention times for both the drug and internal standard. Recovery and reproducibility assessments indicated good accuracy (overall mean relative recovery of 102.7%) and precision (coefficient of variation of 4.4 to 7.7%) for CGP 33101 over the concentration range of 50-4000 ng/mL. The limit of quantification (LOQ) is 50 ng/mL. The method has been successfully applied to a clinical study in which normal volunteers received single oral doses of 400-1200 mg of this new drug candidate.

Quantitative determination of a new anticonvulsant (CGS 18416A) in human plasma using capillary gas chromatography/mass spectrometry

An analytical method has been developed for the determination of a new antiepileptic drug, CGS 18416A, in human plasma. CGS 18416A is a new anticonvulsant representative of a novel class of water-soluble agents being developed for the treatment of epilepsy. Preclinical trials indicate sustained efficacy at relatively low oral doses, indicating a need for a sensitive assay. The method is based on capillary gas chromatography/mass spectrometry and utilizes stable isotope-labelled CGS 18416A as the internal standard. Samples (1 mL) are acidified, then washed with pentane/ethyl acetate, followed by liquid/liquid extraction at pH 11 with pentane/ethyl acetate. Extracts are then concentrated and analysed directly by gas chromatography/mass spectrometry. Separation is accomplished on a thick film methylsilicone capillary column. Mass spectrometry was carried out under positive ion ammonia Cl conditions with selected ion monitoring of the protonated molecular ions (m/z = 248 and 252) for CGS 18416A and the 13CD3-CGS 18416A, respectively. Specificity was demonstrated by the lack of interfering peaks at the retention time of CGS 18416A and the internal standard. Recovery and reproducibility assessments indicate good accuracy and precision over the validated concentration range of 0.2-51 ng/mL. The limit of quantification is 0.2 ng/mL and the method has sufficient sensitivity to support clinical trials. This is illustrated with an example of quantification in a normal volunteer following oral dosing.

Quantitative determination of CGS 18102A, a new anxiolytic, in human plasma using capillary gas chromatography/mass spectrometry

CGS 18102A is a novel hexahydrobenzopyranopyridine that has a mixed pharmacological profile of 5-HT-1A agonist and 5-HT-2 antagonist properties. Based upon these mechanisms, the compound is predicted to have anxiolytic efficacy with possible efficacy in depression. Preclinical studies in the rat have shown the drug to be well absorbed and extensively metabolized. Because of the anticipated low plasma levels in humans a gas chromatography/mass spectrometry (GC/MS) analytical method has been developed and validated to determine plasma concentrations of CGS 18102A in early clinical studies. The method utilizes CGS 18416A as the internal standard. Samples (1 mL) were extracted with pentane:ethyl acetate (75:25, v:v). Extracts were then concentrated and analysed directly by GC/MS. Separation was accomplished on a methylsilicone capillary column (30 m x 0.32 mm i.d.). GC/MS was carried out under positive ion ammonia CI conditions, with selected ion monitoring of the [M + H]+ ions (m/z = 262 and 248) for CGS 18102A and CGS 18416A, respectively. The method was successively applied to the analysis of clinical samples from an ascending multidose safety and tolerability study conducted in six normal healthy male volunteers.

Relationship between systemic drug absorption and gastrointestinal transit after the simultaneous oral administration of carbamazepine as a controlled-release system and as a suspension of 15N-labelled drug to healthy volunteers

1. Plasma drug concentrations after a single oral administration of a suspension of carbamazepine (CBZ) and a 20/200 CBZ Oros osmotic pump system were measured in eight healthy male volunteers. The oral suspension contained 100 mg CBZ labelled with the stable isotope nitrogen-15, whilst the Oros contained 200 mg unlabelled CBZ. Plasma concentrations of [15N]-CBZ and CBZ were measured simultaneously by gas chromatography-mass spectrometry. 2. The position of the CBZ Oros (labelled with indium-111) in the gastrointestinal tract was followed by gamma scintigraphy. Plasma drug concentrations after the two treatments were used to relate pharmacokinetic with transit data. 3. The Oros was taken after breakfast and gastric emptying occurred between 1.1- greater than h post-dosing (median, 5.3 h). Small intestinal transit times ranged from 1.5- greater than 3.6 h, with a median of 2.2 h. There were wide individual variations in colonic transit, and the total transit time ranged from 10-60 h (median, 22 h). 4. Relative systemic bioavailability of CBZ from the Oros was reduced compared with that from the suspension (mean dose normalised AUC ratio = 0.69 +/- 0.17; mean dose-normalised AUC ratio = 0.85 +/- 0.13, allowing for actual release from the Oros system). 5. The in vivo absorption of drug into the systemic circulation from the Oros was estimated using the Wagner-Nelson method. This showed that absorption of CBZ was rapid when the Oros was present in the stomach and small intestine, the rate being determined by the release of drug from the system.(ABSTRACT TRUNCATED AT 250 WORDS)