Efficacy of DRIVEN-FLOW® M7-II, a new on-site drug screening kit in postmortem urine compared with Triage DOA®.

The efficacy of DRIVEN-FLOW® M7-II(DFM7II) for seven drug groups was compared with Triage DOA® (Triage) using 340 autopsy urine samples taken from bodies within 1 month of death based on mass screening analysis of GC/MS and LC-MS/MS. The sensitivity to benzodiazepines was 0.56 in Triage and 0.53 in DFM7II with few false positives, and their accuracy was 0.88. Triage detected triazolo diazepine derivatives more easily than DFM7II. DFM7II detected diazepam and nitro benzodiazepines more easily than Triage. There were nine amphetamine false-positive cases of more than 10 days after death in Triage, but these were absent in DFM7II during this period. The accuracy of amphetamines for Triage was 0.96 and for DFM7II was 1. Tricyclic antidepressant (TCA) was detected in five cases by mass analysis, while there were four false-positive cases using Triage and eight cases using DFM7II. In the TCA false-positive cases of both kits, tricyclic psychotics such as chlorpromazine, carbamazepine, and quetiapine were included as well as the drug poisoning cases. There were no samples containing cocaine or THC. The accuracy of DFM7II for opiate and barbiturates was 1, but those of Triage was less than 1. Based on the above, DFM7II is a more accurate kit with fewer false-positives for target drug groups, other than TCA, than Triage.

UPLC-MS/MS determination of suvorexant in urine by a simplified dispersive liquid-liquid micro-extraction followed by ultrasound assisted back extraction from solidified floating organic droplets.

Suvorexant is a novel sedative/hypnotic drug approved for treatment of insomnia. It has significant forensic importance due to its hypnotic and depressant effects on central nervous system. In this study, a highly sensitive UPLC-MS/MS assay was developed and validated for the determination of suvorexant in urine sample. A simplified dispersive liquid-liquid microextraction followed by ultrasound assisted back extraction from solidified floating organic droplets was employed for sample preparation. The 20 µL of 1-undecanol and 200 µL of acetonitrile were used as extraction solvent and dispersive solvent, respectively. An ultrasound assisted back extraction step was employed to enable the cleanup procedure compatible with mass spectrometric detection. Acquity CSH™C18 column with mobile phase composition of 15 mM ammonium acetate: acetonitrile: formic acid (15:85:0.1%; v/v/v) were used for chromatographic separation. The multiple reaction monitoring transition of 451.12 →104.01 and 451.12→186.04 were used for identification and quantification of suvorexant, respectively, whereas 237.06→194.1 was used for IS in positive mode. The assay demonstrated good linearity in the range of 0.27-1000 ng mL-1 with limit of detection (LOD) and quantification (LOQ) of 0.10 and 0.27 ng mL-1, respectively. Assay validation was performed by following SWGTOX guidelines and all validation results were found to be within acceptable limits. This is the first report of dispersive liquid-liquid microextraction based on solidification of floating organic droplets employed to UPLC-MS/MS for application in biological fluids.

Mass balance, routes of excretion, and pharmacokinetics of investigational oral [14C]-alisertib (MLN8237), an Aurora A kinase inhibitor in patients with advanced solid tumors.

Aims This two-part, phase I study evaluated the mass balance, excretion, pharmacokinetics and safety of the investigational aurora A kinase inhibitor, alisertib, in three patients with advanced malignancies. Methods Part A; patients received a single 35-mg dose of [14C]-alisertib oral solution (~80 µCi total radioactivity [TRA]). Serial blood, urine, and fecal samples were collected up to 336 h post-dose for alisertib mass balance and pharmacokinetics in plasma and urine by liquid chromatography-tandem mass spectrometry, and mass balance/recovery of [14C]-radioactivity in urine and feces by liquid scintillation counting. Part B; patients received non-radiolabeled alisertib 50 mg as enteric-coated tablets twice-daily for 7 days in 21-day cycles. Results In part A, absorption was fast (median plasma Tmax, 1 h) for alisertib and TRA. Mean plasma t1/2 for alisertib and TRA were 23.4 and 42.0 h, respectively. Mean plasma alisertib/TRA AUC0-inf ratio was 0.45, indicating presence of alisertib metabolites in circulation. Mean TRA blood/plasma AUC0-last ratio was 0.60, indicating preferential distribution of drug-related material in plasma. On average, 87.8% and 2.7% of administered radioactivity was recovered in feces and urine, respectively (total recovery, 90.5% by 14 days post-dose). In part B, patients received a median 3 cycles of alisertib. The most common any-grade adverse events were fatigue and alopecia. Conclusions Findings suggest that alisertib is eliminated mainly via feces, consistent with hepatic metabolism and biliary excretion of drug-related material. Further investigation of alisertib pharmacokinetics in patients with moderate-severe hepatic impairment is warranted to inform dosing recommendations in these patient populations.

Identification of Suvorexant in Urine Using Liquid Chromatography-Quadrupole/Time-of-Flight Mass Spectrometry (LC-Q/TOF-MS).

Suvorexant (Belsomra®) is a new hypnotic drug with a novel mechanism of action. In prescribed doses of 10 mg before bedtime, the drug produces rapid onset of sleep by inhibiting the orexin neurons of the arousal system, promoting decreased wakefulness. Suvorexant is a potent and highly selective dual orexin receptor antagonist. Sedative hypnotics are of forensic importance due to their widespread use, potential for additive effects with other central nervous system depressants, impairing effects and potential for misuse. In this report we describe a highly sensitive assay for the identification and quantification of suvorexant in urine. Suvorexant was isolated using liquid/liquid extraction (LLE) and identified using liquid chromatography-quadrupole/time-of-flight mass spectrometry. Suvorexant was quantified using a quadratic calibration model between 5 and 250 ng/mL (R2 = 1.000, n = 6). Processed sample stability was demonstrated for up to 24 h. The limit of detection was 0.5 ng/mL and the limit of quantification (LOQ) was 5 ng/mL. The accuracy, bias and precision of the assay at the LOQ were 99% (81-117%), -1% and 12% (n = 18). Intraassay (n = 5) and interassay (n = 15) precision (% CV) at 10, 50 and 200 ng/mL were ≤8%, and bias ranged from -2% to 4% (98-104% accuracy). No qualitative interferences were detected from matrix, internal standard or 50 common drugs. Matrix effects evaluated at low and high concentrations were -16% and -9%, respectively, and produced CVs of 11% and 5% (n = 20). Suvorexant is a new drug of forensic importance. In this report we describe how a simple acidic/neutral LLE can be used to isolate this lipophilic drug with high recoveries and sound analytical performance.

Quantification of suvorexant in urine using gas chromatography/mass spectrometry.

Suvorexant (Belsomra®) is a novel sedative hypnotic drug that is prescribed to promote sleep in patients with insomnia. It is the first of a new class of drugs classified as dual orexin receptor antagonists (DORAs). Sedative hypnotics with central nervous system depressant effects feature prominently in forensic toxicology investigations. For this reason, a new analytical method was developed to identify suvorexant in urine using liquid-liquid extraction (LLE) and gas chromatography/mass spectrometry (GC/MS). Due to the absence of a commercially available isotopically labeled internal standard, estazolam-D5 was used due to its azepine, triazole and chlorinated functionality. The limit of detection and limit of quantitation was 10ng/mL and the linear range of the assay was 10-1000ng/mL. Accuracy and precision (%CV) were 98-101% and <11% at 30, 250 and 800ng/mL. Interferences from matrix and fifty common drugs were not present and processed samples were stable for 24h at room temperature. Suvorexant is a new drug of significant forensic interest due to its hypnotic and central nervous system depressant effects. The absence of commercially available metabolites and its chromatographic properties present some challenges in terms of identification. Nevertheless, a robust, reliable and sensitive assay was developed to identify suvorexant using GC/MS analysis.

[Comparison of four immunoassay screening devices for detection of benzodiazepine and its metabolites in urine: mainly detection of etizolam, thienodiazepine and its metabolites].

The immunoassay screening of benzodiazepines in urine is one of the most important methods of drug analysis in clinical and forensic laboratories. We experienced an unusual case of poisoning wherein the result of Triage DOA immunoassay screening was negative, although Depas (etizolam) was detected in the blood of the victim who had been suspected to prescribe Depas by gas chromatography-mass spectrometry. Depas has been widely used for the treatment of anxiety in Japan. Three immunoassay screening devices (AccuSign BZO, Monitect-3, and Fastect II) were evaluated for their specificity for etizolam, its 2 major metabolites M-III and M-VI, and other metabolites of benzodiazepines in urine. With AccuSign BZO, etizolam, M-III, and M-VI could be detected at concentrations of 1,000 ng/mL in urine; however, they could not be detected even at concentrations of 25,000 ng/mL with the other kits. In the case of etizolam poisoning, the result of AccuSign BZO was positive; however, Triage DOA, which is mainly used for the detection of drugs in urine at intensive care units (ICUs) or forensic laboratories, showed negative result for benzodiazepines. The concentrations of etizolam and its metabolites in urine were measured by the established high-performance liquid chromatographic method. The concentrations of M-III and M-V were 700 and 1,600 ng/mL, respectively. AccuSign BZO demonstrated higher specificity-than the other screening kits for the detection of etizolam and its metabolites in urine. Therefore, the types of drugs detected would be increased by combining Triage DOA with AccuSign BZO in ICUs or forensic laboratories.

Liquid chromatographic high-throughput analysis of the new ultra-short acting hypnotic 'HIE-124' and its metabolite in mice serum using a monolithic silica column.

For the first time, a fast, high-performance liquid chromatography (HPLC) method was developed and validated for the simultaneous determination of the new ultra-short hypnotic HIE-124 and its metabolite in mice serum. Each compound, together with carbamazepine (internal standard) was extracted from the serum matrix using liquid-liquid extraction (LLE). Chromatographic resolution of the analytes was performed on a Chromolith Speed Rod monolithic silica column (100 mm × 4.6 mm i.d.) under isocratic conditions using a mobile phase of 65:35 (v/v), 20 mM phosphate buffer (pH 7.0 adjusted with phosphoric acid)-acetonitrile. The elution of the analytes were monitored at 240 nm and conducted at ambient temperature. Because of high column efficiency the mobile phase was pumped at a flow rate of 2.5 mL min(-1). The total run time of the assay was 2 min. The method was validated over the range of 60-2000 ng mL(-1) for HIE-124 and 200-1600 ng mL(-1) for the metabolite (r(2) = 0.99). The limit of detection (LOD) for HIE-124 and its metabolite were 20 ng mL(-1) and 65 ng mL(-1), respectively. The proposed method was validated in compliance with ICH guidelines, in terms of accuracy, precision, limits of detection and quantitation and other aspects of analytical validation. The developed method could be used for the trace analyses of HIE-124 and its metabolite in serum and was finally used for the pharmacokinetic study investigation of HIE-124 in mice serum.

Voltammetric sensor for buzepide methiodide determination based on TiO2 nanoparticle-modified carbon paste electrode.

In this work, we have prepared nano-material modified carbon paste electrode (CPE) for the sensing of an antidepressant, buzepide methiodide (BZP) by incorporating TiO2 nanoparticles in carbon paste matrix. Electrochemical studies indicated that the TiO2 nanoparticles efficiently increased the electron transfer kinetics between drug and the electrode. Compared with the nonmodified CPE, the TiO2-modified CPE greatly enhances the oxidation signal of BZP with negative shift in peak potential. Based on this, we have proposed a sensitive, rapid and convenient electrochemical method for the determination of BZP. Under the optimized conditions, the oxidation peak current of BZP is found to be proportional to its concentration in the range of 5 x 10(-8) to 5 x 10(-5)M with a detection limit of 8.2 x 10(-9)M. Finally, this sensing method was successfully applied for the determination of BZP in human blood serum and urine samples with good recoveries.

Strategies on efficient method development of on-line extraction assays for determination of MK-0974 in human plasma and urine using turbulent-flow chromatography and tandem mass spectrometry.

On-line extraction assays using cohesive high-turbulence liquid chromatography (HTLC) coupled with tandem mass spectrometer (MS/MS) have been developed for the determination of MK-0974 in human plasma and urine. In this report, a four-step strategy for efficient method development of an on-line extraction assay was discussed. Several challenges - namely extraction recovery, carryover and analyte loss to urine container - were addressed. The assay procedures included sample preparation on a Packard MultiPROBE II liquid-handling system, direct injection on a Cohesive Flux 2300 system, on-line extraction with a Cohesive C(18) column (0.5mmx50mm, 50microm), HPLC separation on a FluophasePFP column (50mmx3mm, 5microm) under cohesive quick-elution mode and MS detection on a Sciex API4000 in multiple-reaction monitoring (MRM) mode using positive ionization and turbo ion-spray. Since 37-80% analyte loss was observed in urine QCs, 1% BSA was added to bring urine QC accuracy back to approximately 100% of nominal. Because of the nature of BSA, the urine assay was established by adapting the plasma method. Thus, the two assays were able to be validated side-by-side, which reduced the validation time by approximately two-fold. The linear dynamic ranges were 0.5-500 and 1-1000nM for the plasma and urine assays, respectively. Obtained from five standard curves constructed with five lots of human plasma or urine, the intra-day precision (%CV) was <3.14 and <2.62%, and the accuracy was 98.3-101.0 and 99.13-100.64% of nominal for plasma and urine assays, respectively. Both plasma and urine QC samples were stable when kept at room temperature for 4h, at -70 degrees C for 3 weeks, or after three freeze-thaw cycles. Both assays gave reasonable relative recovery (>88.8%) and acceptable matrix effect (<15%). The carryover from the upper limit of quantification (ULOQ) was able to be controlled at <20% of lower limit of quantification (LLOQ).

[The metabolic transformation of (-)-securinine].

AIM: To study the in vitro and in vivo metabolism of (-)-securinine. METHODS: The metabolic transformation of (-)-securinine was studied by using phenobarbital-induced rat liver microsomal incubate containing the NADPH-generating system in vitro and the constitution of the system was optimized. A reversed phase HPLC method was established to analyze the parent drug and its metabolites. The major metabolites were isolated and purified by liquid-liquid extraction, preparative TLC and HPLC, and their structures were elucidated as 6-hydroxyl securinine, 6-carbonyl securinine, 5 beta-hydroxyl securinine and 5 alpha-hydroxyl securinine by 1HNMR, 13CNMR and MS spectral analysis. An HPLC method was developed to analyze securinine and its metabolites in biofluids (bile, urine) of rat. The bile, urine and their enzymatic hydrolyzed samples of the rat i.p. administrated with (-)-securinine were determined by using this method. RESULTS: Four main metabolites of (-)-securinine in rat hepatic microsome incubation were obtained and their structures were elucidated. Metabolites from in vitro study were confirmed in biofluids (bile, urine) which were collected from rats given securinine i.p. It was suggested that 6-hydroxyl securinine was excreted in conjugated form as well by analyzing enzymatic hydrolyzed bile. CONCLUSION: The main metabolic pathway of (-)-securinine in vitro and in vivo is basically elucidated.

[Study on the chiral separation of securinine by high-performance capillary electrophoresis and its stereoselective metabolism in rat].

AIM: To establish a high-performance capillary electrophoresis (HPCE) chiral separation method for d-securinine and l-securinine, and use this method to investigate the stereoselective metabolism process of d- and l-securinine in Wistar rats. METHODS: The electrophoretic condition and parameters were investigated and the optimized conditions were as following: the electrophoretic medium was 40 mmol.L-1 Tris-H3PO4 buffer (pH adjusted to 6.0 with H3PO4) containing 32 mmol.L-1 HP-beta-CD as chiral selector. Determination was carried out with a UV detector at 254 nm. The separations were performed at 16 degrees C with a positive voltage of 15 kV. Samples were injected into the capillary by pressure for 6 s. The biological samples (urine, bile, plasma and feces) of rats were alkalized and extracted with ethyl acetate. RESULTS: The experimental results showed that the concentration of HP-beta-CD, the concentration of the running buffer and the pH value of the buffer were the main important factors which effected the resolution. d-Securinine and l-securinine were separated at baseline level under the determination conditions. The determination was not interfered by endogenous components and metabolites. After i.p. administration, the rats excreted more d-securinine than l-securinine through bile, urine and feces. The metabolism process in rats was stereoselective. CONCLUSION: This method is simple, reliable and suitable for studying the stereoselective metabolism of securinine in rats.

Determination of the anti-platelet-activating factor BN-50727 and metabolites in human urine by high-performance liquid chromatography using solid-phase extraction.

A sensitive and selective HPLC solid-phase extraction procedure was developed for the determination of platelet-activating factor antagonist BN-50727 and its metabolites in human urine. The procedure consisted in a double solid-phase extraction of the urine samples on cyanopropyl and silica cartridges, followed by an automated solid-phase extraction of the drug and metabolites on CBA cartridges and posterior elution on-line to the chromatographic system for its separation. The method allowed quantitation in the concentration range 10-2400 ng/ml urine for both BN-50727 and the main metabolite, the O-demethylated BN-50727 product. The limit of quantitation for both compounds was 10 ng/ml. The inter-assay precision of the method, expressed as relative standard deviation, ranged from 1.9 to 4.5% for BN-50727 and from 2.5 to 9.0% for the metabolite. The accuracy, expressed as relative error, ranged from -2.4 to 4.2% and from 0.2 to 6.2%, respectively. This paper describes the validation of the analytical methodology for the determination of BN-50727 in human urine and also for its metabolites. The method has been used to follow the time course of BN-50727 and its metabolites in human urine after single-dose administration.

Quantitative measurement of BN50727 in human plasma and urine by combined liquid chromatography/negative ion chemical ionization mass spectrometry using a particle beam interface.

A new sensitive assay has been developed for the quantitative measurement of BN50727 at the picomole level in human plasma and urine. The drug and the internal standard (BN50788) were measured by combined liquid chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. A simple solid-liquid extraction procedure was used to isolate BN50727 from the complex biological matrices. The mass spectrometer was tuned to monitor the intense and stable ion at m/z 333 which was generated in the ion source by a dissociative capture process. This assay was performed with 1 ml of plasma or 0.1 ml of urine and the quantification limit of the method was statistically calculated as 1 ng ml-1. The very low relative standard deviations and mean percentages of error calculated during the different within-day or between-day repeatability assays have clearly demonstrated the ruggedness of the technique for the routine determination of BN50727 in biological fluids. Some preliminary results on the pharmacokinetics of the drug are presented to illustrate the applicability of this powerful liquid chromatographic/mass spectrometric method.

Quantitative measurement of a new synthetic hetrazepine derivative, BN50730, in human plasma and urine by combined liquid chromatography-negative chemical ionization mass spectrometry using a particle beam interface.

A new simple and sensitive assay has been developed for the quantitative measurement of BN50730 at the picomole level in human plasma and urine. The drug and the internal standard (BN50765) were measured by combined liquid chromatography-negative chemical ionization mass spectrometry with methane as the reagent gas. A simple solid-liquid extraction procedure was used to isolate BN50730 from complex biological matrices. Mild operating conditions were required to assay the parent drug with a particle beam interface from Hewlett-Packard. The mass spectrometer was tuned to monitor the intense ion m/z 333, which was generated in the ion source by a dissociative capture process. This assay was performed with 1 ml of plasma or 0.1 ml of urine, and the quantification limit of the method was statistically calculated as 1 ng ml-1. The very low relative standard deviation and mean percentage of error calculated during the different within-day or between-day repeatability assays clearly demonstrate the ruggedness of the technique for the routine determination of BN50730 in the biological fluids. Some preliminary results on the pharmacokinetics of the drug are presented to illustrate the applicability of this new powerful LC-MS method.

Percutaneous absorption of azone following single and multiple doses to human volunteers.

Azone (1-dodecylazacycloheptan-2-one) is an agent that has been shown to enhance percutaneous absorption of drugs. Azone is thought to act by partitioning into skin lipid bilayers and thereby disrupting the structure. An open-label study was done with nine volunteers (two males, seven females; aged 51-76 years) in which Azone cream (1.6%; 100 mg) was topically dosed on a 5 x 10-cm area of the ventral forearm for 21 consecutive days. On days 1, 8, and 15, the Azone cream contained 47 microCi of [14C]Azone. The skin application site was washed with soap and water after each 24-h dosing. Percutaneous absorption was determined by urinary radioactivity excretion. The [14C]Azone was ring labeled [14C-2-cyclo-heptan]. Radiochemical purity was > 98.6% and cold Azone purity was 99%. Percutaneous absorption of the first dose (day 1) was 1.84 +/- 1.56% (SD) of applied dose for 24-h skin application time. Day 8 percutaneous absorption, after repeated application, increased significantly (p < 0.002) to 2.76 +/- 1.91%. Day 15 percutaneous absorption, after continued repeated application, stayed the same at 2.72 +/- 1.21%. In humans, repeated application of Azone results in an initial self-absorption enhancement, probably due to its mechanism of action. However, steady-state percutaneous absorption of Azone is established after this initial change. Thus, Azone can enhance its own absorption as well as that of other compounds. This should be considered relevant for any pharmacological or toxicological evaluation. Washing the skin site of application with soap and water only recovered 1-2% of applied radioactivity. Previous published studies recovered the Azone dose with ethanol washes. Thus, there could potentially be an accumulation of Azone in skin.

Biological monitoring for pesticide absorption.

This paper reviews the development of biological monitoring as a method of assessing absorption of pesticides during occupational exposure. An approach to human volunteer studies to estimate the relationship between exposure to pesticides and excretion of metabolites is described and practical aspects of applying biological monitoring to field studies are considered. Case studies are used to illustrate some of the pitfalls of extrapolating from animals to man and to demonstrate the importance of human volunteer studies in establishing a sound basis for biological monitoring for pesticides.

Metabolic polymorphism of E6123 in rhesus monkey.

1. The metabolic polymorphism of a new thienodiazepine platelet activating factor receptor antagonist (E6123) in rhesus monkey was studied in vivo and in vitro. 2. After i.v. dosing of 14C-E6123, the levels of radioactivity in blood, plasma and red blood cells were higher in poor metabolizers (PMs) with AUC(0-24 h) values which were about 1.3-1.5 times higher than those in extensive metabolizers (EMs). 3. After i.v. dosing of 14C-E6123, radioactivity was excreted rapidly by both EMs and PMs. However, EMs excreted the radioactivity mainly in urine whereas, for PMs, radioactivity was excreted fairly equally in urine and faeces. 4. In vivo and in vitro studies demonstrated that the metabolic polymorphism of E6123 in rhesus monkey is caused by a difference in the hydrolysis of an amide side chain. 5. Our results suggested that there are two types of the enzymes which metabolize E6123 by this route in EMs, but only one type in PMs. 6. The low affinity enzyme in EMs might be the same as the enzyme in PMs, indicating that the metabolic polymorphism of E6123 in rhesus monkey could depend on the existence of a high affinity enzyme.

Blood level, metabolism and excretion of [14C]-brotizolam in mice.

Blood level, metabolite pattern and excretion of [14C]-brotizolam, a hypnotic drug, were studied in mice following oral administration. [14C]-Brotizolam was rapidly absorbed which was indicated by a Tmax of the blood level of 0.5 h. Radioactive compounds were eliminated from the blood with a half-life of 5.6 h. Total excretion of radioactivity, the renal portion of which was 22.4%, was complete after 4 days. [14C]-Brotizolam was almost completely metabolized. Using TLC, HPLC and radioactivity measurement, the main metabolite in bile, urine and plasma was found to be brotizolam hydroxylated at the methyl group. Other major metabolites were brotizolam hydroxylated at the diazepine ring and a combination of both hydroxylations. In the bile, all metabolites were conjugated. The metabolism of brotizolam in mice is similar to that in dogs, monkeys and man but not in rats.

Disposition and metabolic profiling of the penetration enhancer Azone. I. In vitro studies: urinary profiles of hamster, rat, monkey, and man.

Chain-labeled 14C-Azone was intravenously administered to hamster, monkey, and rat, to compare its metabolic profile with that obtained previously in humans after dermal application. Azone-derived radioactivity was excreted predominantly in the urine for both hamster and monkey, which is similar to the disposition in humans. Metabolic profiling in urine revealed extensive systemic metabolism to occur in all species studied. The main fraction of the metabolites was most polar in man, followed by rat, monkey, and hamster. Traces of the parent compound were detectable only in hamster urine. Although some of the polar major human metabolites were also present in rat urine, the animals were unsuitable for collecting metabolites of Azone observed in humans. In rats, complete cleavage of the dodecyl side chain was ruled out by administering Azone that had been labeled at two distinct positions of the molecule. Additionally, oral administration of Azone to rats resulted in the same metabolic profile as intravenous administration, indicating that gastrointestinal metabolism does not occur or is similar to systemic metabolism.

Quantitative aspects of the urinary excretion of meptazinol and its metabolites in human volunteers.

1. The urinary excretion of meptazinol and its metabolites has been studied in five healthy human volunteers following oral administration of 200 mg of the 3H-labelled drug. 2. Meptazinol was well absorbed, with 90% of the radioactivity excreted in the urine; elimination of drug-related material took place rapidly. 3. Metabolism was extensive, no unchanged material being detected in the urine. Following selective enzymic hydrolysis the major metabolites were identified as glucuronide and sulphate conjugates of the parent drug present in an approximate ratio of 4:1. 4. A number of minor metabolites, also present in conjugated form, were tentatively identified.