In vitro characterization of protonitazene metabolites, using human liver microsomes, and first application to two urines collected from death cases.

Protonitazene, or N,N-diethyl-5-nitro-2-[(4-propoxyphenyl)methyl]-1H-benzimidazole-1-ethanamine, is a novel synthetic opioid, which belongs to the nitazene family. Over the last four years, nitazenes have re-emerged on the new psychoactive substances market and have been reported in several fatal intoxication cases. The metabolism of several nitazene analogues have already been studied, but to date, no data exists regarding protonitazene. The aim of the study was the detection of protonitazene and its metabolites in authentic human urine collected in two fatal intoxication cases, comparing the data after in vitro incubation with human liver microsomes, and subsequent analysis by ultra-performance liquid chromatography-tandem mass spectrometry and ultra-performance liquid chromatography-high-resolution mass spectrometry. Protonitazene metabolites, including N-desethyl-protonitazene, 5-amino-protonitazene and 4-hydroxy-nitazene, were characterized in vitro and were identified in the urine of both cases. The ratios between metabolites and parent protonitazene, higher than 1, were calculated to estimate the proportionality of metabolites. The results suggest that testing protonitazene metabolites should increase the window detection of exposure to protonitazene.

Investigation of Bemethyl Biotransformation Pathways by Combination of LC-MS/HRMS and In Silico Methods.

Bemethyl is an actoprotector, an antihypoxant, and a moderate psychostimulant. Even though the therapeutic effectiveness of bemethyl is well documented, there is a gap in knowledge regarding its metabolic products and their quantitative and qualitative characteristics. Since 2018, bemethyl is included to the Monitoring Program of the World Anti-Doping Agency, which highlights the challenge of identifying its urinary metabolites. The objective of the study was to investigate the biotransformation pathways of bemethyl using a combination of liquid chromatography-high-resolution mass spectrometry and in silico studies. Metabolites were analyzed in a 24 h rat urine collected after oral administration of bemethyl at a single dose of 330 mg/kg. The urine samples were prepared for analysis by a procedure developed in the present work and analyzed by high performance liquid chromatography-tandem mass spectrometry. For the first time, nine metabolites of bemethyl with six molecular formulas were identified in rat urine. The most abundant metabolite was a benzimidazole-acetylcysteine conjugate; this biotransformation pathway is associated with the detoxification of xenobiotics. The BioTransformer and GLORY computational tools were used to predict bemethyl metabolites in silico. The molecular docking of bemethyl and its derivatives to the binding site of glutathione S-transferase has revealed the mechanism of bemethyl conjugation with glutathione. The findings will help to understand the pharmacokinetics and pharmacodynamics of actoprotectors and to improve antihypoxant and adaptogenic therapy.

Development and Greenness Evaluation of Spectrofluorometric Methods for Flibanserin Determination in Dosage Form and Human Urine Samples.

Green, economic and sensitive two spectrofluorometric methods were developed for the quantitation of flibanserin (FB) in different matrices, which are based on FB native fluorescence properties. The first technique depends on measuring the relative fluorescence intensity of FB directly at emission and excitation wavelengths(λem/λex) (371 nm/247 nm), while the second technique is a first derivative (D1) spectrofluorometric method, which depends on measuring the peak amplitudes at 351 nm. Linear regressions were observed in the range of 0.1-1.5 µg/mL for both methods. Moreover, both methods were efficiently extended to analyze FB in human urine, indicating the ultra-sensitivity of the methods, and linear regression was found within a range 0.05-0.7 µg/mL for both methods. Excellent selectivity of the proposed methods and good recoveries were obtained upon the analysis of FB in pharmaceutical dosage form and human urine samples without interference from matrix components with acceptable ranges, from 98.86 to 101.46% and from 98.08 to 102.37%, respectively. Greenness of the developed methods was assessed using the national environmental method index (NEMI) and Analytical Eco-scale and Green Analytical Procedure Index (GAPI). The three approaches confirmed that the developed methods are green, safe and environment-friendly.

High viral load predicts virologic failure in chronic genotype 2 hepatitis C virus-infected patients receiving glecaprevir/pibrentasvir therapy.

BACKGROUND: The real-world data of glecaprevir/pibrentasvir (GLE/PIB) therapy for patients with chronic hepatitis C virus (HCV) genotype 2 infection remained limited. We aimed to evaluate the possible predictors of virological failure and side effects of GLE/PIB therapy for chronic genotype 2 HCV-infected patients in a real-world setting. METHODS: A total of 326 compensated HCV genotype 2 patients treated with GLE/PIB 12 weeks for cirrhotic patients (n = 56) and 8 weeks for non-cirrhotic patients (n = 270) were enrolled. RESULTS: The sustained virological response 12 weeks off therapy (SVR12) was 98.1%, 100%, and 97.7% in overall, GLE/PIB 12-week, and 8-week group, respectively. There were 6 (1.8%) patients with early withdrawal, and 14.1% patients had pruritus, the major adverse effect. In multivariate analyses, end-stage renal disease (odds ratio (OR) = 4.056, 95% confidence interval (CI) = 1.477-11.14, p = 0.007) and hypertension (OR = 2.325, 95% CI = 1.171-4.616, p = 0.016) were two significant factors associated with pruritus. There were 6 patients with virologic failure. In patients receiving 8-week GLE/PIB therapy, the SVR12 rate was significant lower in high baseline viral load (≥107 IU/ml) group compared to low viral load group (90.6% v.s 98.7%, p = 0.025). Multivariate analyses showed that HCV RNA≥107 IU/ml was one of the independent factors (OR = 0.134, 95% CI = 0.024-0.748; p = 0.022) associated with SVR12. CONCLUSION: GIE/PIB is an effective, tolerable and safe agent to treat genotype 2 HCV infected patients. However, high viral load (≥107 IU/ml) may predict virologic failure in non-cirrhotic patients receiving 8 weeks GIE/PIB treatment. This result should be further validated in a large cohort in the future.

Update on metabolism of abemaciclib: In silico, in vitro, and in vivo metabolite identification and characterization using high resolution mass spectrometry.

Abemaciclib was approved by the US Food and Drug Administration in 2015 as an advanced treatment for metastatic breast cancer. Identification and characterization of limited numbers of abemaciclib metabolites have been reported in the literature. Therefore, the current study focused on the investigation of the in vitro and in vivo metabolic fate of abemaciclib using high resolution mass spectrometry. Initially, a vulnerable site of metabolism was predicted by the Xenosite web predictor tool. Later, in vitro metabolites were identified from pooled rat liver microsomes, rat S9 fractions, and human liver microsomes. Finally, in vivo metabolites have been detected in plasma, urine, and feces matrix of male Sprague-Dawley rats. A total of 12 putative metabolites (11 phase I and 1 phase II) of abemaciclib and their metabolic pathways were proposed by considering accurate mass, mass fragmentation pattern, nitrogen rule, and ring double bonds of the detected metabolites. Abemaciclib was metabolized via hydroxylation, N-oxidation, N-dealkylation, oxidative deamination followed by reduction and sulfate conjugation. In the human liver microsomes, maximum numbers of metabolites (11 metabolites) were observed, from which M7, M8, M9, and M11 were human specific.

A high-performance liquid chromatography-tandem mass spectrometry method for the determination of lifrafenib, a novel RAF kinase and EGFR inhibitor, in human plasma and urine and its application in clinical pharmacokinetic study.

Lifirafenib (BGB-283), a dual inhibitor trageting BRAF kinase and EGFR, showed favorable efficacy and safety in treating patients with different cancer types harboring mutations in BRAF, KRAS and NRAS. In order to support the clinical pharmacokinetic study, a sensitive high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed and validated to quantify lifirafenib concentration in human plasma and urine. Plasma samples were purified using protein precipitation. Urine samples were pre-treated by adding tween 80 with the purpose of preventing non-specific adsorption, then extracted by centrifugation. Chromatographic separation was achieved on Phenomenex Luna C18 column with a gradient elution. The mass detection was performed using electrospray ionization (ESI) source under multiple reaction monitoring (MRM) in positive ionization mode. The method was fully validated, and the result of inter-assay and intra-assay precisions were less than 15% and the accuracy within the scope of ±15%. The linear range for plasma and urine covered from 10 to 10,000 ng/mL and 1 to 200 ng/mL, respectively, with correlation coefficients of 0.99. The validation for matrix effect, recovery, stability and carryover were met the acceptance criteria. The method showed robust and sensitive, it successfully fulfilled the requirement of clinical pharmacokinetic study of lifirafenib in Chinese patients with locally advanced or metastatic solid tumors.

Collision cross section (CCS) as a complementary parameter to characterize human and veterinary drugs.

In the context of human and veterinary drugs identification, ion mobility spectrometry (IMS) in combination with mass spectrometry (MS) may provide a relevant complementary piece of information to mass-to-charge ratio (m/z), the so-called collision-cross-section (CCS). Up to now, however, the application of CCS as identification parameter has not been fully investigated due to the reduced number of these drugs that have being characterized in terms of CCS. This work proposes a CCS database for 92 human and veterinary drugs, including eighteen benzimidazoles, eleven 5-nitroimidazoles, eleven aminoglycosides, nineteen quinolones, eighteen ß-lactams, ten sulfonamides and five tetracyclines. Among them, 37 drugs have been characterized in terms of CCS for the first time. The CCS values of the other 55 compounds have been compared with those from a recently published database in order to evaluate inter-laboratory reproducibility, which is crucial for the implementation of the CCS as identification parameter. CCS values were measured by traveling wave ion mobility spectrometry (TWIMS) under positive ionization conditions. Nitrogen was used as drift gas in the ion mobility cell. The proposed database covers 173 ions including [M+H]+ and [M+Na]+ species. High correlation between m/z and CCS has been observed for [M+H]+ (R2 = 0.9518, n = 91) and [M+Na]+ (R2 = 0.9135, n = 82) ions. As expected, CCS values for sodium adducts are generally greater than for protonated molecules because they exhibit higher molecular weight. However, sodium adducts of aminoglycosides, ß-lactams, and of several quinolones and benzimidazoles, were characterized as more compact ions than their related protonated molecule. In addition, this work describes the fragmentation pattern observed for the studied molecules. For the first time, the main fragment ions for most of the compounds have also been characterized in terms of CCS, involving a total of 238 ions. As proof of concept, for the application of this database to biological matrices, eleven veterinary drugs in bovine urine samples were characterized in terms of CCS, showing that this parameter was not influenced by the matrix.

Detection of bemitil and its metabolite in urine by means of LC-MS/MS in view of doping control analysis.

2-(Ethylthio) benzimidazole is an active ingredient of Antihot, a dietary supplement sold in Ukraine. The substance, available also under names of Bemitil, Metaprot, and Bemaktor, was developed in the USSR in 1970s, and after tests on Soviet cosmonauts and soldiers, several studies on its influence on athletes' performances were conducted. The research showed that bemitil is a synthetic adaptogen which is capable to significantly increase physical performance and reduce the time of regeneration. Moreover, according to supplement's distributor, the substance improves both physical performance and resistance to stress. Taking into account these properties, it appears plausible that the World Anti-Doping Agency (WADA) decided to include bemitil in its 2018 monitoring program. To select markers of bemitil use, six doses of the supplement (two per day, on three consecutive days) were administrated to six healthy volunteers (three men, three women, 26-49 years). Urine samples were collected before, during and up to 30 days after the first ingestion. Samples were analyzed by means of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The study revealed that bemitil can be traced in urine as either a parent compound or its glucuronide conjugate, which is more abundant and has a wider detection window.

Coupling sweeping-micellar electrokinetic chromatography with tandem mass spectrometry for the therapeutic monitoring of benzimidazoles in animal urine by dilute and shoot.

A new method based on micellar electrokinetic chromatography-tandem mass spectrometry (MEKC-MS/MS) has been developed for the identification and simultaneous quantification of thirteen benzimidazoles in animal urine. In order to obtain an appropriate separation with the highest sensitivity, different electrophoretic parameters were evaluated. Under optimum conditions, the separation was performed using ammonium perfluorooctanoate as volatile surfactant and electrophoretic buffer (50mM, pH 9). To increase the sensitivity, a stacking mode named sweeping was applied, using water as injection solvent at 50mbar for 75s, obtaining sensitivity enhancement factors from 50 to 181. The method was applied to different animal urine samples, including sheep, cow and goat. The sample treatment consisted of a 1:10 (v/v) dilution with water. Calibration using sheep urine samples can be used for both goat and cow urine samples with a relative bias below 25% and relative standard deviations lower than 8%. The limits of detection were below 70µgL-1. As a result, the applicability of this rapid, simple, sensitive, and environmentally friendly method for therapeutic drug monitoring of benzimidazoles based on the analysis of animal urine has been demonstrated.

Preconcentration and determination of 2-mercaptobenzimidazole by dispersive liquid-liquid microextraction and experimental design.

A method was developed to determine 2-mercaptobenzimidazole in water and urine samples using dispersive liquid-liquid microextraction technique coupled with ultraviolet-visible spectrophotometry. It was essential to peruse the effect of all parameters that can likely influence the performance of extraction. The influence of parameters, such as dispersive and extraction solvent volume and sample volume, on dispersive liquid-liquid microextraction was studied. The optimization was carried out by the central composite design method. The central composite design optimization method resulted in 1.10 mL dispersive solvent, 138.46 µL extraction solvent, and 4.46 mL sample volume. Under the optimal terms, the calibration curve was linear over the range of 0.003-0.18 and 0.007-0.18 µg/mL in water and urine samples, respectively. The limit of detection and quantification of the proposed approach for 2-mercaptobenzimidazole were 0.013 and 0.044 µg/mL in water samples and 0.016 and 0.052 µg/mL in urine samples, respectively. The method was successfully applied to determination of 2-mercaptobenzimidazole in urine and water samples.

Determination of selumetinib, N-desmethyl selumetinib and selumetinib amide in human biological samples by LC-MS/MS.

AIM: Selumetinib is an inhibitor of MEK1/2 in Phase III development that has activity in multiple tumor types. Validated bioanalytical methods were required to quantitate selumetinib and its N-desmethyl and amide metabolites in a variety of human biological matrices. Methodology & results: LC-MS/MS assays were developed and validated that demonstrated acceptable precision, accuracy and selectivity for selumetinib and the two metabolites in human plasma, urine, blood dialysate and plasma ultrafiltrate. Incurred sample re-analysis was acceptable and issues observed in plasma with the amide metabolite, due to potential instability, were addressed. CONCLUSION: Robust and sensitive LC-MS/MS assays for the quantification of selumetinib and two of its metabolites were validated in human biological matrices and are being used to support the clinical development program.

Matrix Effect Compensation in Small-Molecule Profiling for an LC-TOF Platform Using Multicomponent Postcolumn Infusion.

The possible presence of matrix effect is one of the main concerns in liquid chromatography-mass spectrometry (LC-MS)-driven bioanalysis due to its impact on the reliability of the obtained quantitative results. Here we propose an approach to correct for the matrix effect in LC-MS with electrospray ionization using postcolumn infusion of eight internal standards (PCI-IS). We applied this approach to a generic ultraperformance liquid chromatography-time-of-flight (UHPLC-TOF) platform developed for small-molecule profiling with a main focus on drugs. Different urine samples were spiked with 19 drugs with different physicochemical properties and analyzed in order to study matrix effect (in absolute and relative terms). Furthermore, calibration curves for each analyte were constructed and quality control samples at different concentration levels were analyzed to check the applicability of this approach in quantitative analysis. The matrix effect profiles of the PCI-ISs were different: this confirms that the matrix effect is compound-dependent, and therefore the most suitable PCI-IS has to be chosen for each analyte. Chromatograms were reconstructed using analyte and PCI-IS responses, which were used to develop an optimized method which compensates for variation in ionization efficiency. The approach presented here improved the results in terms of matrix effect dramatically. Furthermore, calibration curves of higher quality are obtained, dynamic range is enhanced, and accuracy and precision of QC samples is increased. The use of PCI-ISs is a very promising step toward an analytical platform free of matrix effect, which can make LC-MS analysis even more successful, adding a higher reliability in quantification to its intrinsic high sensitivity and selectivity.

Development of a molecularly imprinted solid-phase extraction sorbent for the selective extraction of telmisartan from human urine.

A novel molecularly imprinted solid-phase extraction with spectrofluorimetry method has been developed for the selective extraction of telmisartan from human urine. Molecularly imprinted polymers were prepared by a noncovalent imprinting approach through UV-radical polymerization using telmisartan as a template molecule, 2-dimethylamino ethyl methacrylate as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, N,N-azobisisobutyronitrile as an initiator, chloroform as a porogen. Molecularly imprinted polymers and nonimprinted control polymer sorbents were dry-packed into solid-phase extraction cartridges, and eluates from cartridges were analyzed using a spectrofluorimeter. Limit of detection and limit of quantitation values were 11.0 and 36.0 ng/mL, respectively. A very high imprinting factor (16.1) was achieved and recovery values for the telmisartan spiked in human urine were in the range of 76.1-79.1%. In addition, relatively low within-day (0.14-1.6%) and between-day (0.11-1.31%) precision values were obtained. Valsartan was used to evaluate the selectivity of sorbent as well. As a result, a sensitive, selective, and simple molecularly imprinted solid-phase extraction with spectrofluorimetry method has been developed and successfully applied to the direct determination telmisartan in human urine.

Mass balance, metabolite profile, and in vitro-in vivo comparison of clearance pathways of deleobuvir, a hepatitis C virus polymerase inhibitor.

The pharmacokinetics, mass balance, and metabolism of deleobuvir, a hepatitis C virus (HCV) polymerase inhibitor, were assessed in healthy subjects following a single oral dose of 800 mg of [(14)C]deleobuvir (100 µCi). The overall recovery of radioactivity was 95.2%, with 95.1% recovered from feces. Deleobuvir had moderate to high clearance, and the half-life of deleobuvir and radioactivity in plasma were ∼ 3 h, indicating that there were no metabolites with half-lives significantly longer than that of the parent. The most frequently reported adverse events (in 6 of 12 subjects) were gastrointestinal disorders. Two major metabolites of deleobuvir were identified in plasma: an acyl glucuronide and an alkene reduction metabolite formed in the gastrointestinal (GI) tract by gut bacteria (CD 6168), representing ∼ 20% and 15% of the total drug-related material, respectively. Deleobuvir and CD 6168 were the main components in the fecal samples, each representing ∼ 30 to 35% of the dose. The majority of the remaining radioactivity found in the fecal samples (∼ 21% of the dose) was accounted for by three metabolites in which deleobuvir underwent both alkene reduction and monohydroxylation. In fresh human hepatocytes that form biliary canaliculi in sandwich cultures, the biliary excretion for these excretory metabolites was markedly higher than that for deleobuvir and CD 6168, implying that rapid biliary elimination upon hepatic formation may underlie the absence of these metabolites in circulation. The low in vitro clearance was not predictive of the observed in vivo clearance, likely because major deleobuvir biotransformation occurred by non-CYP450-mediated enzymes that are not well represented in hepatocyte-based in vitro models.

Multiresidue analysis of pesticides in urine of healthy adult companion dogs.

The objective of this study was to determine the background exposures to pesticides as detected in urine from 21 healthy companion dogs in Northern Colorado. A panel of 301 pesticides was used to screen urine samples collected from dogs using an established ultraperformance liquid chromatography-mass spectrometry (UPLC-MS/MS) platform. Canine food intakes were controlled for one month on diets that were also screened for pesticide contents. Fifteen distinct pesticides were detected in urine. The most frequently detected compounds in canine urine samples collected over a 1 month period were atrazine, fuberidazole, imidacloprid, terbumeton, and clopyralid. Fuberidazole was the only pesticide detected in both the diets and urine. Companion dogs develop many similar chronic diseases as humans and represent a relevant model for biomonitoring combinations of environmental pesticide exposures, as well as for evaluating the potential relationships between environmental exposures and disease risk.

Novel methods for assessing oral direct factor Xa and thrombin inhibitors: use of point-of-care testing and urine samples.

Rivaroxaban and dabigatran are new oral anticoagulants (NOACs) that inhibit directly factor Xa and thrombin, respectively. These NOACs effectively prevent thromboembolic complications using fixed doses without the need for dose adjustment according to laboratory results. About 60% of rivaroxaban is cleared from circulation by glomerular filtration, 30% of which is excreted as active drug. About 80% of dabigatran is excreted into urine as active compound. Accordingly, both NOACs can be determined in urine by means of chromatographic methods. Only a few laboratories are able to perform such methods, and results are not available within short time frames. New methods have to be developed to obtain results within minutes and possibly as point-of-care (POC) techniques. This testing may be useful for special patient populations such as those with acute deterioration of renal function due to any disease, before surgical interventions, during unexpected bleeding or thrombotic episodes while on therapy with NOACs, the oldest and youngest populations, pregnancy, suspicion of overdose and intoxication, and to determine adherence to therapy. Here we describe results of a POC qualitative assay using urine samples from patients on treatment with dabigatran and rivaroxaban.

Excretion of compound M-11 and its metabolites with urine and feces in rats.

The excretion of compound M-11 and its metabolites with the urine and feces was studied in rats after intraperitoneal and oral administration in a dose of 25 mg/kg. Experiments showed that 1% metabolites were detected in excretions over 24 h irrespective of the route of administration, while the initial compound was not found even in trace amounts.

Trace analysis of three antihistamines in human urine by on-line single drop liquid-liquid-liquid microextraction coupled to sweeping micellar electrokinetic chromatography and its application to pharmacokinetic study.

A rapid and efficient dual preconcentration method of on-line single drop liquid-liquid-liquid microextraction (SD-LLLME) coupled to sweeping micellar electrokinetic chromatography (MEKC) was developed for trace analysis of three antihistamines (mizolastine, chlorpheniramine and pheniramine) in human urine. Three analytes were firstly extracted from donor phase (4 mL urine sample) adjusted to alkaline condition (0.5 M NaOH). The unionized analytes were subsequently extracted into a drop of n-octanol layered over the urine sample, and then into a microdrop of acceptor phase (100 mM H(3)PO(4)) suspended from a capillary inlet. The enriched acceptor phase was on-line injected into capillary with a height difference and then analyzed directly by sweeping MEKC. Good linear relationships were obtained for all analytes in a range of 6.25 × 10(-6) to 2.5 × 10(-4)g/L with correlation coefficients (r) higher than 0.987. The proposed method achieved limits of detections (LOD) varied from 1.2 × 10(-7) to 9.5 × 10(-7)g/L based on a signal-to-noise of 3 (S/N=3) with 751- to 1372-fold increases in detection sensitivity for analytes, and it was successfully applied to the pharmacokinetic study of three antihistamines in human urine after an oral administration. The results demonstrated that this method was a promising combination for the rapid trace analysis of antihistamines in human urine with the advantages of operation simplicity, high enrichment factor and little solvent consumption.

Real-time 2D separation by LC × differential ion mobility hyphenated to mass spectrometry.

The liquid chromatography-mass spectrometry (LC-MS) analysis of complex samples such as biological fluid extracts is widespread when searching for new biomarkers as in metabolomics. The success of this hyphenation resides in the orthogonality of both separation techniques. However, there are frequent cases where compounds are co-eluting and the resolving power of mass spectrometry (MS) is not sufficient (e.g., isobaric compounds and interfering isotopic clusters). Different strategies are discussed to solve these cases and a mixture of eight compounds (i.e., bromazepam, chlorprothixene, clonapzepam, fendiline, flusilazol, oxfendazole, oxycodone, and pamaquine) with identical nominal mass (i.e., m/z 316) is taken to illustrate them. Among the different approaches, high-resolution mass spectrometry or liquid chromatography (i.e., UHPLC) can easily separate these compounds. Another technique, mostly used with low resolving power MS analyzers, is differential ion mobility spectrometry (DMS), where analytes are gas-phase separated according to their size-to-charge ratio. Detailed investigations of the addition of different polar modifiers (i.e., methanol, ethanol, and isopropanol) into the transport gas (nitrogen) to enhance the peak capacity of the technique were carried out. Finally, a complex urine sample fortified with 36 compounds of various chemical properties was analyzed by real-time 2D separation LC×DMS-MS(/MS). The addition of this orthogonal gas-phase separation technique in the LC-MS(/MS) hyphenation greatly improved data quality by resolving composite MS/MS spectra, which is mandatory in metabolomics when performing database generation and search.

[Pharmacokinetics of afobazole metabolite (M-11) in rats].

Pharmacokinetics of compound M-11 (main metabolite of afobazole) after administration via different routes was studied in rats. After oral and intravenous administration, M-11 exhibited weakly pronounced bioconversion with the formation of a few metabolites that could be detected in plasma samples for about 3 hours. The absolute bioavailability of M-11 after oral administration was 68.3%. It was found that M-11 was completely absorbed from gastrointestinal tract of rats and characterized by "the first pass effect", after which approximately 70% of administered dose entered the circulation. The parent substance was determined neither in urine nor in feces.