Simultaneous determination of dextromethorphan, dextrorphan and doxylamine in human plasma by HPLC coupled to electrospray ionization tandem mass spectrometry: Application to a pharmacokinetic study

Incorporation of doxylamine and N-doxylamine-oxide in human hair and the impact of a permanent oxidative hair dye

Knowledge of the drug incorporation in hair and impact of cosmetic treatments remains essential to correctly interpret forensic cases. The study shows the analysis of doxylamine and doxylamine-N-oxide and the evaluation of the relationship between dose and hair concentration and the impact of hair treatment (oxidative dying). The study included (A) three subjects participated to the study: a regular user (Subject 1) and two single-dose users (Subject 2, 1 single dose; and Subject 3, 2 single doses spaced 5 months apart). Subject 3 applied a permanent oxidative hair dying monthly. (B) A permanent oxidative hair dying was applied twice to the hair collected from Subject 2. (A) The average concentrations in head hair for doxylamine and its N-doxylamine-oxide, respectively, were as follows: Subject 1, 1825 pg/mg and 16 pg/mg; Subject 2, 182 and Collapse

Key Words

• N-doxylamine-oxide
• cosmetic treatment
• doxylamine
• hair
• interpretation

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Affiliation(s)

Maria Del Mar Ramirez Fernandez Department of Toxicology, National Institute of Criminalistics and Criminology, Brussels, Belgium
Sarah M R Wille Department of Toxicology, National Institute of Criminalistics and Criminology, Brussels, Belgium
Nele Samyn Department of Toxicology, National Institute of Criminalistics and Criminology, Brussels, Belgium

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Low-volume plasma sampling for determination of dextromethorphan and dextrorphan in rat plasma: LC-MS/MS method and its application in pharmacokinetic study

Dextromethorphan (DM) and its metabolite dextrorphan (DX) continue to draw the attention of researchers owing to their diverse pharmacodynamics. Thus, there are possibilities for repurposing DM. Most of the pharmacodynamics of DM needs further validation in different preclinical models. Also, it is necessary to correlate the pharmacodynamics with relevant pharmacokinetics data. Multiple bioanalytical techniques developed for this purpose primarily use a high sample processing volume. Since sample volume is a limiting factor for many preclinical models, an effort was taken to develop an alternative method suitable for handling low sample processing volumes. An efficient solid-phase extraction technique, robust liquid chromatographic (LC) separation and highly sensitive tandem mass spectrometric detection (MS/MS) showed suitability for use of a 30 μl sample processing volume. This led to the development of a highly specific, selective, accurate and precise-bio-analytical method for simultaneous quantification of DM and DX in rat plasma. The validated method was linear in the range of 0.196-403.356 ng/ml for DM and 0.102-209.017 ng/ml for DX. The application of the method was demonstrated through the estimation of pharmacokinetic parameters that showed good congruence with earlier studies.

A simple and sensitive LC-MS/MS method for determination of doxylamine in human plasma and its application in a bioequivalence study in healthy Chinese volunteers

A simple, rapid, sensitive and specific LC-MS/MS method was developed and validated for the quantitative determination of doxylamine in human plasma, using isotope doxylamine-d5 as internal standard (IS). The detection was conducted on a QTRAP 5500 tandem mass spectrometer coupled with electrospray ionization (ESI) source in positive ion mode. Quantification was achieved by positive electrospray ionization containing multiple reaction monitoring (MRM) transitions of m/z 271.0→182.0 for doxylamine and m/z 276.2→187.3 for IS. The mobile phase A was methanol, and mobile phase B was 20 mM ammonium acetate (0.2 % formic acid) in water, using a gradient elution procedure at a flow rate of 0.6 mL/min. The method was validated with a sensitivity of 0.500 ng/mL and a linear concentration range of 0.500-200 ng/mL. The inter-batch precision (%CV) was less than 5.4 %, and the accuracy deviation (%RE) ranged from - 10.6 % to 3.7 %; the inter-batch precision (%CV) was less than 6.6 %, and the accuracy deviation (%RE) was ranged from - 2.7 % to 0.1 %. The selectivity, sensitivity, extraction recovery, matrix effect, carryover, dilution reliability, stability and other characteristics were within the acceptable range. This validated method was successfully applied to a bioequivalence study that orally administered 25 mg of doxylamine succinate tablets in 60 healthy Chinese volunteers.

Infant dextromethorphan and dextrorphan exposure via breast milk from mothers who are CYP2D6 extensive metabolizers

The risk of infant exposure to dextromethorphan (DM) and its active metabolite, dextrorphan (DX), through breast milk has not been evaluated. In this study, bound and unbound DM and DX concentrations in breast milk and plasma at 2 h post-dose were measured in 20 lactating women (n = 20) following a single 30 mg oral dose of DM. The DM and DX concentrations in breast milk were positively correlated with their respective plasma concentrations. The breast milk-to-plasma (M/P) ratios of 1.0 and 1.6 and the unbound M/P ratios of 1.1 and 2.0 for DM and DX, respectively, suggested that DM and DX are extensively distributed into breast milk. The infant exposure following a single dose of 30 mg DM was estimated using the breast milk concentrations to be 0.33 ± 0.32 μg/kg/day and 1.8 ± 1.0 μg/kg/day for DM and DX, respectively. The steady-state infant exposure was estimated using the M/P ratios and previously reported AUC of DM and DX following repeated dosing of DM 60 mg orally twice daily to be 0.64 ± 0.22 μg/kg/day and 1.23 ± 0.38 μg/kg/day, respectively. Based on these estimated infant doses, the relative infant doses (RIDs) were estimated to be <1%, suggesting the infant is only exposed to a minor fraction of adult dose through breast milk; however, one nursing infant developed an erythematous rash during this study which warrants additional research to fully elucidate the risks of infant exposure to DM and DX through breast milk. This article is protected by copyright. All rights reserved.

A stability-indicating HPLC method for estimation of doxylamine succinate in tablets and characterization of its major alkaline stress degradation product

Background

A new selective rapid RP-HPLC-DAD method was developed and evaluated for the quantification of doxylamine succinate (DOX) in bulk and pharmaceutical dosage form. The separation of DOX at different degradation conditions was achieved with a Kromasil C18 (4.6 × 250 mm, 5-μm particle size). The mobile phase employed comprised of phosphate buffer (pH 3.5) and methanol in the ratio of 45:55 v/v. The flow rate was kept maintained at 1.0 ml/min and eluents were detected at 262 nm. The drug was subjected to different stress conditions like acid, base, neutral, hydrolysis, oxidation, photolysis, and thermal degradation. The analytical performance of the proposed HPLC method was thoroughly validated in terms of linearity, precision, accuracy, specificity, robustness, detection, and quantification limits.

Results

The method produces linear responses that were found in the range of 10–50 μg/ml. The regression equation was found to be Y = 42984x − 10260. The correlation coefficient was found to be 0.9998. The LOD and LOQ for DOX were found to be 0.96 and 3.28 μg/ml, respectively. The short-term solution stability of DOX (100 μg/ml) was evaluated under (25 ± 2°C) storage condition and found to be 98.82 to 101%. The percentage recovery for DOX was in the range of 99.73 to 99.91%. The obtained results of the stress degradation study and peak purity data indicate the potential of the developed HPLC method to resolve degradants from DOX peak. The major alkaline degradation product was isolated using preparative chromatographic technique and extensive FT-IR was performed to ascertain the structure of the alkaline degradant.

Conclusion

It was concluded that the proposed method was simple, sensitive, accurate, cost-effective, and less time-consuming for the quantification of DOX. This method was successfully utilized for stability testing of commercially available DOX tablets. Hence, the proposed method can be applied for routine quality control of DOX in bulk drug as well as in marketed formulations.

Chiral separation of five antihistamine drug enantiomers and enantioselective pharmacokinetic study of carbinoxamine in rat plasma by HPLC-MS/MS

Chiral separation and pharmacokinetic study of antihistamine drugs.

A novel and simple LC–MS/MS quantitative method for dextromethorphan and dextrorphan in oral fluid

Aim: To develop and validate a simple method using LC–MS/MS for determination of dextromethorphan (DXM) and dextrorphan (DT) in human oral fluid. Results: Following protein precipitation, chromatographic separation used a phenyl column with isocratic elution (1 ml/min) of 10 mM ammonium-formate buffer and acetonitrile (65:35; v/v) with 0.1% formic acid. Retention times were 2.6 min for DT and 5 min for DXM. Total run time was 7 min. The intra- and inter-assay deviations (accuracy) for DT (1–100 ng/ml) and DXM (5–1000 ng/ml) ranged from -13.6 to 8.8% and -9.6 to 5.7%, respectively. Precision variations were ≤7.5%. Matrix effect was ≤11.8%. Conclusion: This method may prove helpful for quantification of DT and DXM in oral fluid for either clinical or toxicological purposes.

UPLC-MS/MS analysis of dextromethorphan-O-demethylation kinetics in rat brain microsomes

Formation of dextrorphan (DXT) from dextromethorphan (DXM) has been widely used to assess cytochrome P450 2D (CYP2D) activity. Additionally, the kinetics of CYP2D activity have been well characterized in the liver microsomes. However, studies in brain microsomes are limited due to the lower microsomal content and abundance of CYP2D in the brain relative to the liver. In the present study, we developed a micro-scale enzymatic incubation method, coupled with a sensitive UPLC-MS/MS assay for the quantitation of the rate of DXT formation from DXM in brain microsomes. Rat brain microsomes were incubated with different concentrations of DXM for various times. The reaction was stopped, and the proteins were precipitated by the addition of acetonitrile, containing internal standard (d₃-DXT). After centrifugation, supernatant (2 μL) was injected onto a UPLC, C18 column with gradient elution. Analytes were quantitated using triple-quadrupole MS/MS with electrospray ionization in positive ion mode. The assay, which was validated for accuracy and precision in the linear range of 0.25 nM to 100 nM DXT, has a lower limit of quantitation of 0.125 fmol on the column. Using our optimized incubation and quantitation methods, we were able to reduce the incubation volume (25 μL), microsomal protein amount (5 μg), and incubation time (20 min), compared with reported methods. The method was successfully applied to estimation of the Michaelis-Menten (MM) kinetic parameters of dextromethorphan-O-demethylase activity in the rat brain microsomes (mean ± SD, n = 4), which showed a maximum velocity of 2.24 ± 0.42 pmol/min/mg and a MM constant of 282 ± 62 μM. It is concluded that by requiring far less biological material and time, our method represents a significant improvement over the existing techniques for investigation of CYP2D activity in rat brain microsomes.

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.

Development and validation of a sensitive UHPLC-MS/MS method for the simultaneous analysis of tramadol, dextromethorphan chlorpheniramine and their major metabolites in human plasma in forensic context: application to pharmacokinetics

The prerequisites for forensic confirmatory analysis by LC/MS/MS with respect to European Union guidelines are chromatographic separation, a minimum number of two MS/MS transitions to obtain the required identification points and predefined thresholds for the variability of the relative intensities of the MS/MS transitions (MRM transitions) in samples and reference standards. In the present study, a fast, sensitive and robust method to quantify tramadol, chlorpheniramine, dextromethorphan and their major metabolites, O-desmethyltramadol, dsmethyl-chlorpheniramine and dextrophan, respectively, in human plasma using ibuprofen as internal standard (IS) is described. The analytes and the IS were extracted from plasma by a liquid-liquid extraction method using ethyl acetate-diethyl-ether (1:1). Extracted samples were analyzed by ultra-high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS). Chromatographic separation was performed by pumping the mobile phase containing acetonitrile, water and formic acid (89.2:11.7:0.1) for 2.0 min at a flow rate of 0.25 μL/min into a Hypersil-Gold C18 column, 20 × 2.0 mm (1.9 µm) from Thermoscientific, New York, USA. The calibration curve was linear for the six analytes. The intraday precision (RSD) and accuracy (RE) of the method were 3-9.8 and -1.7-4.5%, respectively. The analytical procedure herein described was used to assess the pharmacokinetics of the analytes in 24 healthy volunteers after a single oral dose containing 50 mg of tramadol hydrochloride, 3 mg chlorpheniramine maleate and 15 mg of dextromethorphan hydrobromide.

Determination of lomerizine in human plasma by liquid chromatography/tandem mass spectrometry and its application to a pharmacokinetic study

A rapid, sensitive and selective high performance liquid chromatography-electrospray ionization-tandem mass spectrometry method (HPLC-ESI-MS/MS) was developed and validated for the determination and pharmacokinetic investigation of lomerizine in human plasma. Protein precipitation process was used to extract lomerizine from human plasma. Plasma samples were separated by HPLC on an Agela Venusil XBP Phenyl column (100 mm × 2.1 mm, 5 μm) using a mobile phase consisting of methanol-2mM ammonium acetate-formic acid (70:30:0.1, v/v/v) and the flow rate was set at 0.35 mL/min. The total run time was 4.0 min and the elution of lomerizine was at 1.9 min. The detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction-monitoring (MRM) mode using the respective [M+H](+) ions m/z 469.2→181.0 for lomerizine and m/z 405.2→202.9 for the I.S. The calibration curve was linear over the range of 0.1-25 ng/mL (r(2)>0.99) with a limit of quantitation (LOQ) of 0.1 ng/mL. The intra- and inter-day precision (relative standard deviation, RSD) values were below 9.65% and the mean accuracy was from 99.00 to 103.00% at four quality control levels. Lomerizine was stable during stability studies, i.e., long term, auto-sampler and freeze/thaw cycles. The method was successfully applied for the evaluation of pharmacokinetics of lomerizine after single oral doses of 10 mg lomerizine to 18 healthy volunteers.

Pharmacokinetics and oral bioavailability of epimedin C after oral administration of epimedin C and Herba Epimedii extract in rats

Epimedin C, an ingredient of Herba Epimedii, has potential for treatment of cardiovascular disease and bone loss. However, there is still no sensitive analytical method to monitor epimedin C in biological samples. The goal of this study was to develop a sensitive and reliable method based on a LC-MS/MS for evaluating the pharmacokinetics of epimedin C after administration of Herba Epimedii in rat. Electrospray ionization in positive-ion mode and multiple reaction monitoring were used to identify and quantitate active components. Analytes were separated by a reverse-phase C18 column. Liquid-liquid extraction using ethyl acetate, evaporation and reconstitution was used to plasma sample preparation. Mass transition of precursor ion → product ion pairs were monitored at m/z 823.4 → 313.1 for epimedin C and m/z 237.1 → 178.9 for carbamazepine (internal standard). A calibration curve gave good linearity (r > 0.999) over the concentration range 2.5-500 ng/mL. Pharmacokinetic data demonstrated that there was rapid distribution and slow elimination after epimedin C administration (1 mg/kg, i.v.). Oral bioavailabilities of epimedin C in the pure compound and in the Herba Epimedii were around 0.58% and 0.13%, respectively. The result suggests that other herbal ingredients of Herba Epimedii may suppress the oral bioavailability of epimedin C.

Food effects on the pharmacokinetics of doxylamine hydrogen succinate 25 mg film-coated tablets: a single-dose, randomized, two-period crossover study in healthy volunteers

BACKGROUND

Doxylamine succinate, an ethanolamine-based antihistamine, is used in the short-term management of insomnia because of its sedative effects. The data available on the pharmacokinetic profile of doxylamine in humans are limited, notwithstanding that this drug has been marketed in European countries for more than 50 years. In fact, no data on the effect of food on the pharmacokinetic parameters of doxylamine are available.

OBJECTIVE

The objective of this study was to evaluate the pharmacokinetic parameters of doxylamine following a single oral dose of doxylamine hydrogen succinate 25 mg in healthy human subjects under fed and fasting conditions.

STUDY DESIGN

This was a single-center, randomized, single-dose, laboratory-blinded, two-period, two-sequence, crossover study.

SETTING

The study was conducted in a phase I clinical unit.

SUBJECTS AND METHODS

A single oral dose of doxylamine hydrogen succinate 25 mg (equivalent to 17.4 mg of doxylamine base) was administered to healthy volunteers under either fed conditions (high-fat, high-calorie food intake) or fasting conditions in each study period. The drug administrations were separated by a wash-out period of seven calendar days. Plasma samples were collected for up to 60 hours postdose, and plasma doxylamine concentrations were determined by a high-performance liquid chromatography method with tandem mass spectrometry detection. Pharmacokinetic parameters were calculated using noncompartmental analysis. Safety was evaluated through assessment of adverse events, standard laboratory evaluations, vital signs, and 12-lead electrocardiography.

RESULTS

In total, 24 healthy subjects (12 male and 12 female) were included in the study. Doxylamine succinate 25 mg tablets exhibited similar oral bioavailability of doxylamine in the fasting state (mean maximum plasma drug concentration [C(max)] 118.21 ng/mL, coefficient of variation [CV] 19.2%; mean area under the plasma concentration time curve from time zero to time t [AUC(t)] 1746.97 ng · h/mL, CV 31.6%) and in the fed state (mean C(max) 120.99 ng/mL, CV 15.0%; mean AUC(t) 1712.20 ng · h/mL, CV 26.7%). No statistically significant between-treatment differences were observed for any of the pharmacokinetic parameters under study. The fed : fasting ratios of the geometric least squares means with corresponding 90% confidence intervals for C(max) and AUC(t) were within the range of 80-125%.

CONCLUSION

High-fat, high-calorie food intake does not affect the kinetics of doxylamine in healthy subjects. The drug was safe and well tolerated by the subjects in this study.