Toxicological detection of pholcodine in blood, urine and hair in three cases of fatal intoxication.

Pholcodine is an opioid antitussive reputed for its low toxicity and absence of addictive effect. We report three cases of pholcodine intoxication with fatal outcome. Large concentrations of pholcodine were quantified by gas chromatography coupled to mass spectrometry (GC/MS) in peripheral postmortem blood (respectively 2890 ng/mL, 979 ng/mL and 12,280 ng/mL). Segmental hair analyses by GC/MS and detected pholcodine in three 1.5-2 cm segments (38-161 ng/mg, 8.54-41.6 ng/mg, and 0.26-2.66 ng/mg, respectively). These findings underline that pholcodine can be involved in fatal poisoning and raise the question of misuse or abuse and of taking account of this drug in opioid overdose prevention policies.

Pharmacokinetics of dextromethorphan and its metabolites in horses following a single oral administration.

Dextromethorphan is an N-methyl-D-aspartate (NMDA) non-competitive antagonist commonly used in human medicine as an antitussive. Dextromethorphan is metabolized in humans by cytochrome P450 2D6 into dextrorphan, which is reported to be more potent than the parent compound. The goal of this study is to describe the metabolism of and determine the pharmacokinetics of dextromethorphan and its major metabolites following oral administration to horses. A total of 23 horses received a single oral dose of 2 mg/kg. Blood samples were collected at time 0 and at various times up to 96 h post drug administration. Urine samples were collected from 12 horses up to 120 h post administration. Plasma and urine samples were analyzed using liquid chromatography-mass spectrometry, and the resulting data analyzed using non-compartmental analysis. The Cmax , Tmax , and the t1/2 of dextromethorphan were 519.4 ng/mL, 0.55 h, and 12.4 h respectively. The area under the curve of dextromethorphan, free dextrorphan, and conjugated dextrorphan were 563.8, 2.19, and 6,691 h*ng/mL respectively. In addition to free and glucuronidated dextrorphan, several additional glucuronide metabolites were identified in plasma, including hydroxyl-desmethyl dextrorphan, desmethyl dextrorphan, and three forms of hydroxylated dextrorphan. Dextromethorphan was found to be eliminated from the urine predominately as the O-demethylated metabolite, dextrorphan. Several additional metabolites including several novel hydroxy-dextrorphan metabolites were also detected in the urine in both free and glucuronidated forms. No significant undesirable behavioural effects were noted throughout the duration of the study. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of the Chinese herbal formula "Zuojin Pill" on the pharmacokinetics of dextromethorphan in healthy Chinese volunteers with CYP2D6*10 genotype.

OBJECTIVE: Zuojin Pill has been shown to inhibit the cytochrome P450 (CYP) 2D6 isoenzyme in vitro. In Chinese individuals, CYP 2D6*10 is the most common allele with reduced enzyme activity. In this study, we investigated the pharmacokinetic interaction between Zuojin Pill and the sensitive CYP2D6 probe dextromethorphan in healthy Chinese volunteers with CYP2D6*10 genotype. METHODS: A pharmacokinetics interaction study was carried out in three groups with CYP2D6*1/*1 (n = 6), CYP2D6*1/*10 (n = 6), and CYP2D6*10/*10 (n = 6) genotypes. Each participant received a single oral dose of dextromethorphan (15 mg) followed by Zuojin Pill (3 g twice daily) for 7 days, and received 3 g Zuojin Pill with 15 mg dextromethorphan in the last day. Blood samples (0-24 h) and urine samples (0-12 h) were collected at baseline and after the administration of Zuojin Pill, and the samples' concentration of dextromethorphan and its main metabolite dextrorphan was determined. RESULTS: Compared to baseline values, co-administration of Zuojin Pill (3 g twice daily) for 7 days increased the AUC0-24 of dextromethorphan [mean (90 % CI)] by 3.00-fold (2.49∼3.61) and 1.71-fold (1.42∼2.06), and decreased oral clearance(CL/F) by 0.27-fold (0.2-0.40) and 0.57-fold (0.48-0.67) in the participants with CYP2D6*1/*1 and CYP2D6*1/*10 genotypes, respectively. In contrast, no significant change was observed in these pharmacokinetic parameters of the participants with CYP2D6*10/*10 genotype. CONCLUSION: These data demonstrated that administration of Zuojin Pill inhibited moderately CYP2D6-mediated metabolism of dextromethorphan in healthy volunteers. The inhibitory influence of CYP2D6 was greater in CYP2D6*1/*1 and CYP2D6*1/*10 groups than CYP2D6 *10/*10 group.

Potential transducers based man-tailored biomimetic sensors for selective recognition of dextromethorphan as an antitussive drug.

A biomimetic potentiometric sensor for specific recognition of dextromethorphan (DXM), a drug classified according to the Drug Enforcement Administration (DEA) as a "drug of concern", is designed and characterized. A molecularly imprinted polymer (MIP), with special molecular recognition properties of DXM, was prepared by thermal polymerization in which DXM acted as template molecule, methacrylic acid (MAA) and acrylonitrile (AN) acted as functional monomers in the presence of ethylene glycol dimethacrylate (EGDMA) as crosslinker. The sensors showed a high selectivity and a sensitive response to the template in aqueous system. Electrochemical evaluation of these sensors revealed near-Nernstian response with slopes of 49.6±0.5 and 53.4±0.5 mV decade(-1) with a detection limit of 1.9×10(-6), and 1.0×10(-6) mol L(-1) DXM with MIP/MAA and MIP/AN membrane based sensors, respectively. Significantly improved accuracy, precision, response time, stability, selectivity and sensitivity were offered by these simple and cost-effective potentiometric sensors compared with other standard techniques. The method has the requisite accuracy, sensitivity and precision to assay DXM in pharmaceutical products.

The effect of grape seed extract on the pharmacokinetics of dextromethorphan in healthy volunteers.

PURPOSE: Grape seed extract (GSE) has been shown to inhibit the cytochrome P450 (CYP) 2D6 isoenzyme in vitro. To determine the clinical effect of GSE on CYP2D6, the pharmacokinetic interaction between GSE and the sensitive CYP2D6 probe dextromethorphan in healthy adult volunteers was examined. METHODS: In this open label, randomized, cross-over study, 30 subjects were assigned to cohort A or B. Both cohorts ingested 30 mg dextromethorphan hydrobromide on day 1 and day 10. Cohort A received 100 mg GSE capsules three times daily on days 8, 9 and 10, while cohort B started with GSE on day -1 until day 1. After urine collection (0-8 h) on day 1 and day 10, the urinary dextromethorphan to dextrorphan metabolic ratio was determined. RESULTS: Among 28 evaluable subjects, an increase of the urinary metabolic ratio was observed in 16 subjects (57 %). The mean metabolic ratio (± standard deviation) before and after GSE supplementation was 0.41 (± 0.56) and 0.48 (± 0.59), respectively. This result was neither statistically (P = 0.342) nor clinically [geometric mean ratio 1.10, 90 % CI (0.93-1.30)] significant. Further, the majority (73 %) of the included subjects did not experience any adverse events after intake of dextromethorphan or GSE. CONCLUSIONS: Supplementation of GSE did not significantly affect the urinary dextromethorphan to dextrorphan metabolic ratio in healthy volunteers. The results of this clinical study indicate that GSE appears to be safe to combine with drugs extensively metabolized by CYP2D6, such as dextromethorphan and tamoxifen.

Determination of the active metabolite of moguisteine in human plasma and urine by LC-ESI-MS method and its application in pharmacokinetic study.

In this study, a sensitive and reproducible electro-spray ionization liquid chromatography-mass spectrometry (LC-ESI-MS) method was established to determine the concentration of M1, the main active metabolite of moguisteine in human plasma and urine. The analysis was performed on a Diamonsil® C18(2) column (150 mm × 4.6 mm, 5 µm) with the mobile phase consisting of 0.1% formic acid-acetonitrile (57:43, v/v, pH=3.0) at a flow rate of 0.8 mL min⁻¹. The pseudo-molecular ions [M+H]+ (m/z 312.2 for M1 and 446.3 for glipizide) were selected as the target ions for quantification in the selected ion monitoring (SIM) mode. Plasma samples were analyzed after being processed by acidification with formic acid and protein precipitation with acetonitrile. Urine samples were appropriately diluted with blank urine for analysis. Calibration curve was ranged from 0.02 to 8 µg mL⁻¹. The extraction recovery in plasma was over 90%. Both the inter- and intra-day precision values were less than 7.5%, and the accuracy was in the range from -6.0% to 6.0%. This is the first reported LC-ESI-MS method for analyzing M1 in human plasma and urine. The method was successfully applied to the pharmacokinetic study after oral administration of single-dose and multiple-dose of moguisteine tablets in healthy Chinese subjects.

Metabolism and excretion studies of oral administered naringin, a putative antitussive, in rats and dogs.

Naringin, a major active flavonone glycoside from a traditional Chinese medicine Huajuhong, has been demonstrated to have activities such as peripheral antitussive, mucoregulator and anti-inflammatory. The purpose of this study was to elucidate the metabolism and mass balance of orally administered naringin in rats and dogs. After oral administration of naringin to rats and dogs at doses of 42 mg/kg and 12.4 mg/kg, respectively, metabolites in excreta were identified using a LC-Q-TOF system. The major metabolites including naringin, total naringenin (including free naringenin and its conjugates) and 4-hydroxyphenylpropionic acid in excreta were quantified by a LC-MS/MS system. Twenty-two metabolites were identified in dogs and 17 metabolites were detected in rats. The observed routes of naringin metabolism were hydroxylation, methylation, acetylation, hydrogenation, deglycosylation, dehydrogenation, glucuronidation, sulfation, glucosylation, ring-fission, oxidation, glycine conjugation and dehydroxylation. On the basis of these identified metabolites, a comprehensive metabolic pathway of naringin was proposed. About 21% of administered naringin was recovered in rat excreta in the form of naringin, total naringenin and 4-hydroxyphenylpropionic acid, and about 60% was recovered in dog excreta. The levels of 4-hydroxyphenylpropionic acid in excreta were higher than those of naringin and total naringenin, and the quantified metabolites were excreted more through feces, rather than urine. Most of these metabolites were excreted within 36 h post dose. The results of metabolism and excretion studies provide an explanation for future pharmacological and toxicological findings and are the groundwork for clinical studies.

Characterization of pentoxyverine metabolites in urine using GC/MS after intoxication with Silomat cough drops.

A nearly two and a half year old boy was hospitalized after showing symptoms of disorientation and hallucination. The parents remembered the child playing with a bottle of Silomat cough drops, so that an intoxication was taken into consideration. After liquid/liquid extraction of a urine sample collected in hospital, the underivatized and the acetylated extracts were analyzed by gas chromatography-mass spectrometry (GC/MS) using electron ionization (EI) as well as chemical ionization (CI). In the urine sample high amounts of pentoxyverine (carbetapentane) and several of its metabolites, e.g., different hydrolyzed, desalkylated and ring-hydroxylated products have been identified. The correlation of the results, the observed symptoms, and the access to the Silomat cough drops reveal an intoxication after ingestion of an unknown amount of the antitussive pentoxyverine. Corresponding EI- and CI-GC/MS spectra are presented characterizing the structure of its metabolites.

Assessment of activity levels for CYP2D6*1, CYP2D6*2, and CYP2D6*41 genes by population pharmacokinetics of dextromethorphan.

The pharmacokinetics of dextromethorphan (DM) is markedly influenced by cytochrome P450 2D6 (CYP2D6) enzyme polymorphisms. The aim of this study was to quantify the effects of the CYP2D6*1, *2, and *41 variants on DM metabolism in vivo and to identify other sources of pharmacokinetic variability. Concentrations of DM and dextrorphan (DO) in plasma and urine were evaluated in 36 healthy Caucasian men. These volunteers participated in three clinical studies and received a single oral dose of 30 mg DM-HBr. Data were modeled simultaneously using the population pharmacokinetics NONMEM software. A five-compartment model adequately described the data. The activity levels of the alleles assessed differed significantly. The clearance attributable to an individual CYP2D6*1 copy was 2.5-fold higher as compared with CYP2D6*2 (5,010 vs. 2,020 l/h), whereas the metabolic activity of CYP2D6*41 was very low (85 l/h). Urinary pH was confirmed as a significant covariate for DM renal clearance. These results refine genotype-based predictions of pharmacokinetics for DM and presumably for other CYP2D6 substrates as well.

Identification of two novel metabolites of SCH 486757, a nociceptin/orphanin FQ peptide receptor agonist, in humans.

The study of human metabolism of endo-8[bis(2-chlorophenyl)methyl]-3-(2-pyrimidinyl)-8-azabicyclo[3.2.1]octan-3-ol (SCH 486757) after a 200-mg oral dose of the drug to healthy volunteers in the first-in-human study is presented. The structural elucidation of two unique metabolites, which were detected in the process of metabolite characterization in human plasma and urine by liquid chromatography-mass spectrometry (LC-MS), is described. These metabolites (M27 and M34) were initially detected in human plasma at high levels (>35% of the LC-MS response of the parent drug). Additional LC-MS experiments (hydrogen/deuterium exchange and accurate mass measurement) were used to determine structures of metabolites. It was found that both metabolites were formed through a loss of the C-C bridge from the tropane moiety with the conversion into a substituted pyridinium compound. This metabolic process has not been reported previously. Because of the apparent high abundance of metabolites based on the LC-MS response, actual circulating amounts of these metabolites relative to the parent drug were determined semiquantitatively to evaluate their coverage in preclinical species. With the use of reference standards, it was shown that the LC-MS response of M27 and M34 in human plasma was much higher than that of the parent compound. Actual amounts of M27 and M34 metabolites were less than 5% of the level of the parent drug; therefore, additional assessment was not required.

Dose-response relationship for the pharmacokinetic interaction of grapefruit juice with dextromethorphan investigated by human urinary metabolite profiles.

Grapefruit juice (GFJ) has been shown to affect the pharmacokinetics of a large number of drugs, essentially by inhibition of efflux transporters and CYP3A4 monooxygenase in the small intestine. The GFJ dose usually used in human studies was one glass single-strength (1x). Information on a respective dose-response relationship is not available. We investigated the effect of GFJ of different concentration (0.25 x, 0.5x, 1x, 2x) dosed in biweekly intervals in 19 volunteers. Components considered responsible for drug interactions, naringin, naringenin, bergamottin, and 6',7'-dihydroxybergamottin were determined by LC-tandem mass spectrometry. Immediately after ingestion of GFJ, participants took an aqueous solution of dextromethorphan (DEX) as probe drug. Urine was collected in two sampling periods, 0-2 and 2-4h, and excreted amounts of DEX and five metabolites associated with CYP3A4 and/or CYP2D6 enzyme activity were determined. Effects of GFJ were analyzed by the Wilcoxon matched-pairs signed-rank test against an average of four water control experiments. Two effects were highly significant: (i) a delay of total metabolite excretion in the first 2h and (ii) an inhibition of the CYP3A4-dependent metabolic pathways. Effect magnitude and significance levels were dose-dependent and indicated 200 ml 1x GFJ as "lowest observed effect level" LOEL.

A validated SIM GC/MS method for the simultaneous determination of dextromethorphan and its metabolites dextrorphan, 3-methoxymorphinan and 3-hydroxymorphinan in biological matrices and its application to in vitro CYP2D6 and CYP3A4 inhibition study.

Dextromethorphan is used as a probe drug for assessing CYP2D6 and CYP3A4 activity in vivo and in vitro. A SIM GC/MS method without derivatization for the simultaneous determination of dextromethorphan and its metabolites, dextrorphan, 3-methoxymorphinan and 3-hydroxymorphinan, in human plasma, urine and in vitro incubation matrix was developed and validated. Calibration curves indicated good linearity with a coefficient of variation (r) better than 0.995. The lower limit of quantitation was found to be 10 ng/mL for all analytes in all matrices. Intra-day and inter-day precision for dextromethorphan and its metabolites was better than 9.02 and 9.91%, respectively and accuracy ranged between 91.76 and 106.27%. Recovery for dextromethorphan, its metabolites and internal standard levallorphan was greater than 72.68%. The method has been successfully applied for the in vitro inhibition of metabolism of dextromethorphan by CYP2D6 and CYP3A4 using known inhibitors of CYPs such as quinidine and verapamil.

Development and validation of ELISA and GC-MS procedures for the quantification of dextromethorphan and its main metabolite dextrorphan in urine and oral fluid.

The development of a highly sensitive enzyme-linked immunosorbent assay and gas chromatography-mass spectrometry confirmation method for the detection of dextromethorphan and its major metabolite dextrorphan in urine and oral fluid is described. For the screening assay, the intraday precision was less than 8% for urine and less than 5% for oral fluid. The interday precision was less than 10% for both drugs in urine and oral fluid. For the confirmatory procedure, both inter- and intraday precision was less than 5% for both matrices. The detection limit for both methods was 1 ng/mL. The quantifying ions chosen from the full scan mass spectra were m/z 271 for dextromethorphan, m/z 329 for dextrorphan, and m/z 332 for tri-deuterated dextrorphan-d(3). A high recovery yield (> 93%) from the Quantisal oral fluid collection device was achieved, and the drugs were stable in the collection device for at least 10 days at room temperature. The extracted drugs from both matrices were stable for at least 48 h while kept at room temperature. Both screening and confirmatory procedures were applied to authentic urine and oral fluid specimens obtained from volunteers following therapeutic ingestion of dextromethorphan.

Standardization of method for the analysis of dextromethorphan in urine.

Dextromethorphan (DMP), an antitussive, is one of the most popular drugs among the younger generation in Korea. It usually is taken for its hallucinogenic properties and overdoses have been responsible for the fatalities that have been reported frequently. To control the abuse of DMP, the authorities restricted its use through classifying it as a controlled drug on October 2003. The purpose of this study is to provide a standard method for the analysis of DMP and its main metabolite, dextrorphan (DTP) in biological specimens. At first we established a standard operating procedure (SOP) for DMP/DTP in urine, and a method validation was performed. We also quantified DMP from 16 drug abuser's urine samples all of which were positive in the screening test for DMP. For the detection of DMP/DTP, urine samples were adjusted with 6N NaOH (pH 11) and extracted with ethylacetate. Thin layer chromatography was used as the screening test, and the final identification for DMP/DTP was used by GC/MS. The ions (m/z 271 for DMP, m/z 257 for DTP and m/z 86 for lidocaine as internal standard) were extracted from the full scan mass spectrum and were used for quantification. The selectivity, linearity of calibration, accuracy, within- and between day precision, limit of detection and quantification, recovery and stability were examined as parts of the method validation. Extracted calibration curves were linear from 100 to 2000 ng/mL for DMP and DTP with correlation coefficients better than 0.999. Limit detection was 50 ng/mL for DMP and DTP. Within-run precision (%CV) for DMP and DTP at three different concentrations (100, 500 and 1000 ng/mL) was 6.10-18.85%, and between-run precision was 1.70-7.86% for DMP and DTP. Absolute recovery for DMP and DTP was 57-74%, and relative recovery (extraction efficiency) was 80-89%. For 16 drug abuser's urine samples, the concentrations of DMP and DTP were 0.16-52.63 and 0.41-23.75 microg/mL, respectively. Method validation is an important requirement in the practice of chemical analysis, and it will be particularly useful in verifying the reliability of analytical results in the field of forensic science.

Identification and quantitative determination of benproperine metabolites in human plasma and urine by liquid chromatography-tandem mass spectrometry.

Two novel metabolites of benproperine (BPP), 1-[1-methyl-2-[2-(phenylmethyl)phenoxy]ethyl]-3-piperidinol (3-OH-BPP) and 1-[1-methyl-2-[2-(phenylmethyl)phenoxy]ethyl]-4-piperidinol (4-OH-BPP), were confirmed by comparison of retention times and mass spectra with those of synthetic standards using liquid chromatography-tandem mass spectrometry. Selective and sensitive procedures were developed for the simultaneous determination of BPP, 3-OH-BPP and 4-OH-BPP in human plasma and urine. The analytes were extracted from plasma sample and enzymatically hydrolyzed urine samples by liquid-liquid extraction, separated through a Diamonsil C(18) column (150 mm x 4.6 mm i.d.) and determined by tandem mass spectrometry with an electrospray ionization interface in selected reaction monitoring mode. Dextromethorphan was used as internal standard. The mobile phase consisted of acetonitrile-water-formic acid (34:66:1, v/v/v), and flow-rate was 0.5 ml min(-1). This method has a lower limit of quantification (LLOQ) of 60, 4.0 and 4.0 nmol l(-1)for BPP, 3-OH-BPP and 4-OH-BPP in plasma, 4.9, 4.7 and 2.4 nmol l(-1) in urine, respectively. The intra- and inter-run precision were measured to be below 9.2%, and the accuracy was within +/-4.3% for the analytes. The method was successfully used to determine BPP, 3-OH-BPP and 4-OH-BPP in plasma and urine for pharmacokinetic investigation. The results indicated residue of 3-OH-BPP in the body at least 192 h after an oral dose of BPP.

Identification of some benproperine metabolites in humans and investigation of their antitussive effect.

AIM: To identify 4 unknown metabolites of benproperine (BPP, 1) in human urine after a po dose, and to investigate the antitussive effect of monohydroxylate metabolites. METHODS: The putative metabolite references were prepared using chemical synthesis. Their structures were identified using 1H and 13C nuclear magnetic resonance, and mass spectrometry. The metabolites in human urine were separated and assayed using liquid chromatography-ion trap mass spectrometry (LC/MS/MS), and further confirmed by comparison of their mass spectra and chromatographic retention times with those of synthesized reference substances. The antitussive effects of metabolites were evaluated on coughs induced by 7.5% citric acid in conscious guinea pigs. RESULTS: 1-[1-Methyl-2-[2-(phenylmethyl)phenoxy]-ethyl]-4-piperidinol (2), 1-[1-methyl-2-[2-(phenylmethyl)phenoxy] ethyl]-3-piperidinol (3) and their glucuronides 4 and 5 were obtained from chemical synthesis. Four urinary metabolites in human urine showed peaks with the same chromatographic retention times and mass spectra in LC/MS/MS as synthetic substances 2, 3, 4 and 5. Phosphates of compounds 2 and 3 prolonged the latency of cough and reduced the number of coughs during the 3 min test using citric acid, but did not reduce the number of coughs during the 5 min immediately after the test in conscious guinea pigs. CONCLUSION: Compounds 2, 3, 4, and 5 were identified as the metabolites of BPP in human urine. Among them, compounds 2 and 3 are inactive in the antitussive effect.

Simultaneous determination of phenytoin and dextromethorphan in urine by solid-phase extraction and HPLC-DAD.

A rapid and simple high-performance liquid chromatographic method with photodiode array detection was developed for the separation and the simultaneous determination of phenytoin and dextromethorphan in human urine. Analysis was performed in less than 4.5 min in isocratic mode on a reversed-phase C18 column (5 microm; 150 x 4.6 mm) using a mobile phase composed of acetonitrile-buffer phosphate 0.01 M (60:40, v/v) adjusted to pH 6.0, at 1 mL/min flow rate and UV absorbance at 210 nm. The elution order of analytes was dextromethorphan (DXM), Internal Standard (IS), and phenytoin (PHT). Calibration curves were linear in the 7.5-25 microg/mL range for PHT and in the 10-30 microg/mL range for DXM. Spike recoveries for urine samples prepared at three spiking levels ranged from 97.8 to 102.3% for PHT and from 94.8 to 100.4% for DXM. The detection limit (LOD) values ranged from 0.08 microg/mL for PHT to 0.5 microg/mL for DXM. The quantitation limit (LOQ) values ranged from 0.3 microg/mL for PHT to 1.6 microg/mL for DXM. The sample preparation method involves a rapid and simple procedure based on solid-phase extraction using a C18 reversed-phase column. Validation of the optimised method was carried out according to the ICH guidelines. The method developed in this study allows the reliable simultaneous analysis of PHT and DXM, drugs that were never quantified together in previously reported analytical methods. The described method has the advantage of being rapid and easy and it could be applied in therapeutic monitoring of these drugs in human urine of epileptic patients.

Studies on the human metabolism and the toxicologic detection of the cough suppressant dropropizine in urine using gas chromatography-mass spectrometry.

Studies are described on the metabolism and the toxicologic analysis of the nonopioid cough suppressant dropropizine [R,S-3-(4-phenyl-1-piperazinyl)1,2-propandiol, DRO] in human urine using gas chromatography-mass spectrometry (GC-MS). The metabolism studies showed that DRO was metabolized in humans mainly by hydroxylation of the aromatic ring, by N-dealkylation of the parent drug and of the hydroxyl-metabolite to the corresponding N-phenylpiperazines, and by degradation of the piperazine moiety. The authors' systematic toxicologic analysis (STA) procedure using full-scan GC-MS after acid hydrolysis, liquid-liquid extraction, and microwave-assisted acetylation allowed the unambiguous detection of DRO and its above-mentioned metabolites in human urine up to about 32 hours after intake of a single common therapeutic dose. The target analytes were found to be the parent compound DRO (earlier phase of excretion) and the hydroxylated metabolite para-hydroxy-DRO (later phase of excretion). Both allowed unambiguous detection of an intake of DRO and also differentiation from other phenylpiperazine derivatives.

Single-point plasma or urine dextromethorphan method for determining CYP3A activity.

Dextromethorphan is used widely in vivo to phenotype the polymorphically expressed cytochrome P450 (CYP) 2D6. Also dextromethorphan is N-demethylated in vivo to 3-methoxymorphinan by human CYP3A4/5. The metabolic ratio (MR) of dextromethorphan/3-methoxymorphinan in plasma, saliva and urinary were examined as a possible in vivo probe of CYP3A activity. In limited previous studies, 4 h urinary samples were collected for determining the MR. To evaluate the repeatability and validity of previously reported and other potential phenotyping methods, the MR from urine samples (at various intervals), from plasma and from saliva (at varying time points) were determined after repetitive single doses of immediate-release or repetitive multiple doses of controlled-release dextromethorphan preparations. For the single-dose study, each of 12 subjects received 15 mg of immediate-release dextromethorphan in periods II and I, respectively, with a 1 week washout period. For the multiple dose study, each of 16 subjects received 60 mg controlled release dextromethorphan twice daily for 5 days in periods I and II, respectively, with a 2 week washout period. Dextromethorphan and 3-methoxymorphinan are assayed by high-performance liquid chromatography. In the single-dose study, all of the urine MR revealed good repeatabilities for the periods (paired t-test). The urine MR at any time interval of 0-6 h, 0-8 h and 0-12 h correlated significantly with the MR from 0-24 h urine (r>0.8, p<0.05). In the multiple-dose study, all MR revealed good repeatabilities for the two periods (paired t-test). The plasma MR at any time between 0.5 h and 12 h, the saliva MR at 12 h and the urine MR at any interval between 0-2 h, 0-4 h, 0-6 h, 0-8 h, 0-12 h and 0-24 h could predict the MR from AUCtau(ss). In conclusion, the urine sample as 0-6 h, 0-8 h or 0-12 h in the single immediate-release dose (15 mg) or in the multiple controlled-release dose (60 mg) procedure, the saliva sample at 12 h, the urine sample at 0-2 h, 0-4 h, 0-6 h, 0-8 h, 0-12 h, 0-24 h or all plasma-sampling points 0.5-12 h could be used as the dextromethorphan MR for determining the CYP3A activity.