Lithium salts are known to treat bipolar disorder. Their high potential as neuroprotective agents in cerebral ischemia determines relevance for preclinical studies for the registration of new drugs based on them. Aim of the study was to investigate the toxic properties and local tolerability with an assessment of the toxicokinetics of the developed lithium chloride preparation for injection in dwarf pigs with repeated intravenous administration. Material and methods. Lithium chloride (solution, for intravenous administration 4.2 %) has been administered to minipigs (control and 3 experimental groups of animals of 3 males and 3 females) for 28 days at doses of 12.6; 29.4 and 63 mg/kg. General toxicity, local irritation, and basic pharmacokinetic parameters (Cmax, AUC0-24, MRT, T1/2, Vss, and Cl) were evaluated. Serum lithium ion concentration was estimated colorimetrically using quinizarin. Results and discussion. Toxic properties of the test drug were revealed, expressed in a change in the clinical state (vomiting after administration, inhibition of behavior and feed refusal), body weight negative dynamics, clinical and laboratory changes, shortening of the “QT” interval, accompanied by abnormalities according to the pathomorphological study results (focal infiltration with single renal tubular necrosis areas, kidneys fibrosis, replacement of thyroid tissue with adipose tissue). There were no signs of locally irritating effects of the test product. To evaluate toxicokinetic parameters, a bioanalytical assay (calibration range – from 0.17 to 5.45 μg/mL) was developed and validated, which is not inferior by its characteristics to the commercial reagent kits. According to the results of biomaterial analysis no lithium accumulation in the pig’s body was found with repeated use of the test drug. Doses of the drug that provide toxic concentrations of lithium (above 3 μg/ml) in the minipig’s serum were identified. The NOAEL was 12.6 mg/kg and the LOAEL was 29.4 mg/kg. Conclusions. The comprehensive approach to the consideration of toxic manifestations and toxicokinetics, including its analytical component of studies of this kind, was noted. The obtained results should be taken into account to assess the benefit/risk ratio in the clinical use of lithium chloride injection.

Relevance. The evaluation of control samples contamination is a necessary element for confirming the correctness of toxicokinetic studies (TK), concomitant with the study of toxicity of drugs and products. At the same time, insufficient elaboration of existing regulatory documents necessitates discussion of practical aspects and improvement of the regulatory framework. Purpose. The work is devoted to the consideration of experimental experience of control samples contamination in TK studies. Materials and methods. As experimental examples, two studies of TK drugs performed using rabbits with oral administration of study drugs for 28 (Study 1) or 90 (Study 2) days were considered. Results. Study 1 revealed a contamination level of 17–25 % (on the first and last days of study drug administration, respectively). Contamination of bioassays can occur in vivo (contamination of animals) and ex vivo (at the stage of bioassay sampling, at the pre-analytical stage and analytical stage). The nature of the analyte detection in the samples made it possible to exclude contamination in vivo, and the results of an internal investigation suggested that it occurred at the stage of biosample selection. In Study 2, a number of preventive measures were implemented and a slight level of contamination was obtained (0.83 %), which did not affect the completeness and correctness of results interpretation. Conclusion. Based on experimental experience, recommendations for minimizing and preventing contamination of control samples during the biological part, pre-analytical and analytical stages of studies were formulated. Presumably, in the presence of a random nature of contamination indicating its ex vivo origin, the level of contamination not exceeding 25 % can be considered insignificant, i.e. not leading to further deviation and cancellation of the results of the entire study

Background. Pembrolizumab belongs to a fundamentally new class of antitumor agents with biological source – monoclonal antibodies. when creating generic biological medicinal products, it is necessary to assess the comparability of the pharmacokinetics of the developed drug and the original (reference) drug product in relevant animal species.Aim. To compare the pharmacokinetics of two drugs with INN pembrolizumab, concentrate for solution for infusion, administered once intravenously to Macaca fascicularis.Materials and methods. Biosimilar RPH-075 (INN pembrolizumab, JSC R-Pharm, Russia) and reference drug Keytruda® (INN pembrolizumab, MSD International GmbH) were administered once intravenously to male monkeys (2 groups of 4 males each) at a dose of 30 mg/kg. Macaque blood samples were collected for analysis before administration and at 1, 2, 4, 8, 24, 48, 72, 144, 312, 480, 648, 984, 1320 h after administration. Plasma concentrations of the active ingredient were determined by bridging ELISA using commercially available antibodies, followed by calculation of the main pharmacokinetic parameters (Cmax, AUC, MRT, Vss, T1/2, Cl).Results. Using antibodies more available than commercial reagent kits, the pembrolizumab assay method recommended by the antibody manufacturer has been replicated. The method has been validated and applied to the analysis of biosamples obtained in the preclinical study. There was no effect of the test drug and the reference drug upon single intravenous administration to monkeys condition and animals body weigh; drugs were found to have comparable pharmacokinetic profiles.Conclusion. The creation of a biosimilar drug in the Russian Federation will improve the treatment of patients with cancer, reduce the cost of treatment and increase the number of patients receiving high-quality medical care.

In pharmacokinetics (PK) studies of medicinal products with small laboratory animals models, primarily rodents, the design of the animal-point experiment is often used, involves the selection of biological material after euthanasia of the animal. The question of experimental data processing and the PK parameters calculation method in a situation where all concentration values are obtained from different individuals is relevant. Purpose of the study . Comparison of pharmacokinetic parameters calculation methods in studies with the animal-point design. Materials and methods . For a number of previously conducted studies with male outbred rats test systems, a retrospective data analysis was performed and PK parameters were calculated in three different ways: from the average concentration values at each time point (method 1): from data obtained for animals with the same sequence numbers in subgroups corresponding to time points (method 2); using resempling based on modeling of individual PK profiles (method 3). Pharmacokinetic parameters (maximum concentration — Cmax, time to reach maximum concentration — Tmax, area under the curve "concentration-time" — AUC0-t, average time to stay in the body — MRT, half-life — T1/2) were calculated by non-compartment method of statistical moments using the validated PKSolver application for Microsoft Office Excel. Results . The comparison of the obtained results did not reveal any patterns and preferences for the use of a particular method of calculating PK parameters depending on the studied drugs, route and administration way. For all evaluated PK parameters (Cmax, Tmax, AUC0-t, MRT, T1/2), similar values and/or intervals were obtained, which indicated the correctness of all considered calculation methods. Conclusion . Based on advantages and disadvantages of the calculation methods comparison it is shown that it is optimal to use method 2, which is a special case of reception (method 3) with a minimum number of replications. It is important to emphasis the method of PK parameters calculation when describing the methodology of studies to improve their quality.

The high prevalence of fungal skin infections motivates expanding the range of sertaconazole products for ex-ternal use. The aim of the study was a preclinical comparison of the safety, antifungal activity, and pharmacokinetics of Sertaverin® 2% medicated shampoo (VERTEX JSC, Russia) with those of Sertamicol® 2% solution for external use (Glenmark Pharmaceuticals Ltd, India) and Nizoral® 2% shampoo (Janssen Pharmaceuticals N.V., Belgium) approved in the Russian Federation. Materials and methods. In the toxicity study, the medicinal products were applied to the skin of male and female outbred rats at doses of 0.5 or 1.5 mL/animal for 28 days. The authors evaluated the pharmacokinetics of two sertaconazole formulations (shampoo and solution) following a single administration to adult male rats at the same dose. Nizoral® was not used in the pharmacokinetics study because it contains a different active substance, ketoconazole. The minimum inhibitory concentration (MIC) was determined using the serial microdilution method in a wide range of concentrations. Results. The medicinal products did not exhibit any significant toxic effects in laboratory animals after 28 days of repeated dermal application. Plasma sertaconazole concentrations were negligible. Sertaconazole was intensively distributed in the liver, which is a highly vascularised organ, and in the target organ (skin at the site of application). The relative bioavailability of sertaconazole from the shampoo relative to that from the solution for external use was approximately 30% in liver tissues and approximately 363% in skin tissues at the application site. Sertaverin® was comparable to sertaconazole in the active substance form in terms of inhibiting the growth of Malassezia furfur strains. The MICs calculated on the active substance basis were ≤16–64 μg/mL. Conclusions. With its synergistic dual mechanism of action, broad-spectrum antifungal activity, lipophilic properties, and low systemic absorption, Sertaverin® may provide a more effective and safe alternative to marketed medicinal products for scalp diseases.

Esomeprazole, the S-isomer of omeprazole, is a second-generation proton pump inhibitor widely used for acid-related diseases of the oesophagus, stomach, and duodenum (peptic ulcer, gastro-oesophageal reflux disease, etc.). Studies on esomeprazole safety and toxicokinetics (TK) are essential for increasing the number of modified-release esomeprazole products manufactured in Russia. The aim of the study was to compare the safety and toxicokinetics of a new esomeprazole product, 40 mg modifiedrelease capsules (Valenta Pharm JSC, Russia), and Nexium ® 40 mg film-coated tablets (AstraZeneca AB, Sweden). Materials and methods. This toxicity study involved oral administration of esomeprazole 40 mg modified-release capsules (Valenta Pharm JSC, Russia) and Nexium ® 40 mg film-coated tablets (AstraZeneca AB, Sweden) to 5 groups of rabbits (8 males and 8 females per group) for 28 days at a dose of 1 or 3 capsules, or tablets, corresponding to approximately 4.8 or 14.3 maximum human therapeutic doses (MHTDs), respectively. Comparisons included general toxicity, local tolerance, safety pharmacology, effects on immune system organs, reproductive toxicity, and basic TK parameters ( C max , T max , AUC 0-24 , MRT , and T 1/2 ). Results. No toxic effects, including local irritation and immunotoxicity, were observed for the test product. The safety pharmacology testing demonstrated the safety of repeated oral administration of the test product for the cardiovascular, excretory, respiratory systems and the liver. The test product did not affect the reproductive system of male and female rabbits. The No Observed Adverse Effect Level (NOAEL) was determined to be 14.3 MHTDs. According to the TK parameters evaluated after single and repeated oral administration, the test product and Nexium ® demonstrated comparable TK profiles. Conclusions. The study demonstrated a favourable safety profile for the test product. All the test product parameters studied were comparable with those of Nexium ® . Positive clinical experience with Nexium ® supports the data obtained for the new esomeprazole product. Thea safety of these medicinal products may be considered similar.

Abstract New analgetic tridecapeptide (TDP) with an octaarginine vector was proposed for clinical use in chronic pain syndrome. The aim of the work was to investigate pharmacokinetic properties of TDP in the form for oral administration. Special analytical approach was proposed because classical chromatographic methods are low powerful for peptides quantification in biological matrices. The study was carried out on male rats and rabbits with a single oral administration of the drug in three doses, a single intravenous administration in one dose and multiple administrations to rats in one dose. To determine TDP concentration in blood plasma, tissues, and excretes, enzyme immunoassay with commercially available reagent kit for similar target analyte (Elisa kit for 1-Deamino 8D-Arginine Vasopressin (DDAVP), Cloud Clone Corp., USA) have been developed and validated. Pharmacokinetic parameters were calculated by noncompartment method of statistical moments.The pharmacokinetics of TDP was found to be linear after single administration in the dose range 10-50 mg/kg for rats and 5-25 mg/kg for rabbits. The absolute bioavailability of the TDP after oral (intragastrical) via intravenous administration for rats and rabbits was about 8-16%.The active substance was intensively distributed into muscles, liver, spleen, the lowest tissue distribution was detected for kidneys. TDP was excreted with urine in trace amounts (about 0.2%), with feces – about 1.2%; repeated administration did not lead to its cumulation. Pharmacokinetics parameters of new analgetic tridecapeptide with an octaarginine vector were evaluated after original analytical approach. Final study included all main areas necessary to characterize the original drug pharmacokinetic.

According to current regulatory views, a comparative study of the pharmacodynamics (PD) of low molecular weight heparin (LMWH) products and confirmation of their equivalence require comparing three PD markers: the anti-Xa activity, the anti-IIa activity, and the tissue factor pathway inhibitor (TFPI) concentration.The aim of this study was to analyse the features specific to the bioanalytical part of an equivalence study of a nadroparin calcium biosimilar after single subcutaneous administration.Material and methods: the anti-Xa and anti-IIa activity values and TFPI content were determined in human plasma samples obtained after single subcutaneous administration of the test and the reference product in the same dose, using commercially available reagent kits and pre-validated assays. The authors calculated the main PD parameters (surrogate pharmacokinetic markers), namely the maximum activity or concentration (Amax or Cmax), time to maximum activity or concentration (Tmax), area under the activity–time (or concentration–time) curve (AUC), and half-life period (T1/2), by means of the model-independent statistical moment analysis and carried out further statistical testing of the parameters.Results: the anti-Xa activity and TFPI concentration results provided for the possibility of calculating and comparing the PD parameters (Amax or Cmax, AUC0-24, AUC0-∞, Tmax, T1/2) and estimating the confidence intervals that are necessary to confirm the bioequivalence of the studied products. The anti-IIa activity data had a characteristic pattern of slight fluctuations around one level, which prevented the calculation and comparison of PD parameters.Conclusion: the study identified specific features to consider when planning comparative PD studies of nadroparin calcium products. Firstly, it is feasible to divide samples into two test aliquots (one for anti-Xa and anti-IIa activity determination, the other for TFPI analysis) at the moment of collection in order to perform the analytical step correctly. Secondly, there is no need in full validation for the bioanalytical assays of the anti-Xa and anti-II activity and TFPI content in human plasma validated in the concentration ranges of 0.024–0.182 IU/mL, 0.0069–0.052 IU/mL and 1.56–100 ng/mL, respectively; a confirmation that the active ingredient does not interfere with the analytical procedure is adequate for the purpose. Finally, the data obtained may not allow for calculating PD parameters and comparing confidence intervals for all three markers. The listed considerations may be relevant for other LMWH products as well.

The high prevalence of fungal skin infections motivates expanding the range of sertaconazole products for external use.The aim of the study was a preclinical comparison of the safety, antifungal activity, and pharmacokinetics of Sertaverin® 2% medicated shampoo (VERTEX JSC, Russia) with those of Sertamicol® 2% solution for external use (Glenmark Pharmaceuticals Ltd, India) and Nizoral® 2% shampoo (Janssen Pharmaceuticals N.V., Belgium) approved in the Russian Federation.Materials and methods. In the toxicity study, the medicinal products were applied to the skin of male and female outbred rats at doses of 0.5 or 1.5 mL/animal for 28 days. The authors evaluated the pharmacokinetics of two sertaconazole formulations (shampoo and solution) following a single administration to adult male rats at the same dose. Nizoral® was not used in the pharmacokinetics study because it contains a different active substance, ketoconazole. The minimum inhibitory concentration (MIC) was determined using the serial microdilution method in a wide range of concentrations.Results. The medicinal products did not exhibit any significant toxic effects in laboratory animals after 28 days of repeated dermal application. Plasma sertaconazole concentrations were negligible. Sertaconazole was intensively distributed in the liver, which is a highly vascularised organ, and in the target organ (skin at the site of application). The relative bioavailability of sertaconazole from the shampoo relative to that from the solution for external use was approximately 30% in liver tissues and approximately 363% in skin tissues at the application site. Sertaverin® was comparable to sertaconazole in the active substance form in terms of inhibiting the growth of Malassezia furfur strains. The MICs calculated on the active substance basis were ≤16–64 μg/mL.Conclusions. With its synergistic dual mechanism of action, broad-spectrum antifungal activity, lipophilic properties, and low systemic absorption, Sertaverin® may provide a more effective and safe alternative to marketed medicinal products for scalp diseases.

Introduction: The pharmacokinetics studies are some of the necessary parts of the drugs preclinical investigations. Pharmacokinetic properties of new peptide drug 1-deamino-arginine-vasotocin (dAVT) in the form of an injection solution for intravenous and intramuscular administration for hypernatremia correction were investigated. Materials and methods: The study was carried out on male rats and rabbits with a single intravenous administration of the drug in three doses, a single intramuscular administration in one dose and multiple administration to rats in one dose. To determine natriiuretic peptide concentration in blood plasma, tissues, and excretes, assays based on a sodium level change measurement using a biochemical analyzer have been developed and validated. Pharmacokinetic parameters were calculated by the model-independent method of statistical moments. Results and discussion: The pharmacokinetics of the drug was found to be linear after a single administration of dAVT drug in the dose range 3–10 μg/kg for rats and rabbits. The relative bioavailability of dAVT after intramuscular and intravenous administrations was more than 30%. After a biomarker content change, the active substance was intensively distributed into highly vascularized organs (spleen), the organs that provide metabolism and subsequent excretion (liver and kidneys), whereas it hardly reached moderately and weakly vascularized tissues (muscles, omentum). Less than 10% dAVT was excreted with urine; no dAVT was determined in feces; and repeated administration did not lead to its cumulation. Conclusion: Pharmacokinetics parameters of new nonapeptide drug 1-deamino-arginine-vasotocin were evaluated after original analytical biomarker approach. The study included all main areas necessary to characterize the original drug pharmacokinetic.

BACKGROUND: Phenosanic acid is a synthetic antioxidant, the active ingredient of the original domestic drug recommended for the treatment of epilepsy. To improve the effectiveness and safety of the use of phenosanoic acid, additional study of its pharmacokinetic properties is necessary. AIM: To study the pharmacokinetic parameters of the active ingredient of the drug Dibufelon, capsule 200 mg (LLC Piq-Pharma, Russia) in vitro and in vivo systems in rats after single administration in one dose. MATERIALS AND METHODS: Phenosanic acid binding to blood plasma proteins, microsomal stability and permeability through the monolayer of Caco-2 cells were evaluated in in vitro tests. The pharmacokinetics parameters were studied after a single intragastric administration in Wistar rats in dose of 80 mg/kg. The samples were analyzed by HPLC-UV. RESULTS: A high variability in the degree of binding of phenosanic acid to blood plasma proteins by 2065% depending on the concentration was revealed, relatively high microsomal stability (half-life 1106 789 min, internal clearance 2.05 0.86 l/min/mg protein of liver microsome; residual content after 60 min incubation 87.9 7.8%) and the ability to penetrate through the monolayer of cells Caco-2. The rapid absorbtion of the substance into the systemic bloodstream was established its maximum concentration in blood plasma was observed already 3.6 1.2 hours after administration, and its slow removal from the systemic bloodstream the half-life was about 19 h, the average retention time was about 29 h. Phenosanic acid with different degrees of intensity was distributed to all the examined organs and tissues: kidneys liver brain omentum muscle, and invariably excreted in a small amount with urine and feces, about 0.04% and 5.5%, respectively. CONCLUSIONS: As a result of the study, it was found that phenosanic acid is characterized by rapid absorbtion into the systemic bloodstream and a long stay in it invariably, which may be due to the peculiarities of its binding to blood plasma proteins and relatively high metabolic stability, revealed during the corresponding in vitro tests. The study of the permeability and transport of phenosanic acid showed that it can presumably be attributed to compounds with medium permeability and is not a substrate for the transport protein P-glycoprotein (P-gp). The study of tissue availability of phenosanic acid confirmed its entry into peripheral tissues, including the brain, which is the area of implementation of the anticonvulsant effect.

Phenosanic acid prevents convulsions, reduces the frequency of epileptic seizures, and improves cognitive, intellectual and mnestic functions in patients with epilepsy. Therefore, phenosanic acid-based medicinal products are promising candidates for inclusion in combination antiepileptic therapy. In order to combine medicinal products rationally and ensure that the therapy is safe, it is useful to study the pharmacokinetic interaction of medicinal products planned for clinical co-administration.The aim of the study was to examine single-dose pharmacokinetic interactions between Dibufelon® 200 mg capsules (PIQ-PHARMA LLC, Russia) and two medicinal products planned for clinical co-application with it, namely, valproic acid and carbamazepine, in sexually mature dogs.Materials and methods: the study included medicinal products of phenosanic acid (Dibufelon® 200 mg capsules by PIQ-PHARMA LLC, Russia), valproic acid (300 mg prolonged-release film-coated tablets), and carbamazepine (200 mg tablets). The medicinal products were administered to beagle dogs (2 groups of 9 males each) as a single oral dose separately and in the following combinations: phenosanic acid with valproic acid and phenosanic acid with carbamazepine. Dose selection involved adjusting maximum human therapeutic doses using interspecies conversion factors. Phenosanic acid was administered at a dose of 24 mg/kg; valproic acid and carbamazepine were administered at a dose of 60 mg/kg. Blood sampling took place at baseline and in 0.5, 0.75, 1, 2, 4, 6, 8, 10, and 24 h after dosing. Plasma concentrations of active substances were determined by HPLC-UV. Pharmacokinetic interactions were evaluated by changes in the main pharmacokinetic parameters (Сmax, Тmax, AUC0-24, MRT, Т1/2).Results: the study demonstrated rapid gastrointestinal absorption and prolonged systemic circulation of phenosanic acid administered separately (Tmax 2–4 h, T1/2 13–28 h) and combined with valproic acid (Tmax 2 h, T1/2 22 h). When administered with carbamazepine, phenosanic acid was eliminated from the systemic blood flow faster (T1/2 7.4 h).Conclusions: co-administration of phenosanic acid and valproic acid medicinal products had no significant effect on their respective pharmacokinetics. Whereas, the combination of phenosanic acid and carbamazepine demonstrated a significant decrease in the Tmax values of phenosanic acid and the MRT values of carbamazepine. The pharmacokinetic changes suggestive of a possible interaction between phenosanic acid and carbamazepine need further clinical investigation.

Инграмон представляет собой пептидный фрагмент (65 – 76) моноцитарного хемотаксического белка-1 (МСР-1) человека, обладающий противовоспалительной активностью. Фармакокинетические параметры инграмона после однократного внутримышечного введения кроликам в дозе 0,5 мг/кг составляют: Cmax = 840 ± 68 нг/мл, Tmax = 0,08 ± 0,00 ч, AUC0-8 = 981 ± 17 ч  нг/мл, AUC0-∞ = 1052 ± 16 ч  нг/мл, MRT = = 1,04 ± 0,04 ч, Т1/2 = 0,70 ± 0,02 ч.

Introduction. The study of pharmacokinetics of medicinal substances and evaluation of their pharmacokinetic parameters is a necessary stage of pharmaceutical development of original medicinal agents, allowing to choose the composition and dosage form of the preparation. This is due to obtaining characteristics of all processes that occur in the body of an animal (human), from the absorption of a drug from the place of administration to its excretion from the body.Aim. To conduct a study of the pharmacokinetics of the pharmaceutical substance and the complex compounds based on it to confirm the pharmaceutical development of a drug of 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil and to justify the optimal composition of the ready dosage form (GLP).Materials and methods. The study was carried out on male rabbits with a single oral administration of investigated objects in one dose. Plasma concentrations of 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil were determined by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection. Pharmacokinetic parameters were calculated by extramodel method of statistical moments.Results and discussion. Assay 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil quantification in rabbit blood plasma by HPLC has been developed and validated in the concentration range 10–720 ng/ml in accordance with modern requirements and satisfies them for all indicators. Assay was applicated to analysis of plasma samples obtained from laboratory animals after a single oral administration of a substance and solid dispersion systems of 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil in one dose. The main pharmacokinetic parameters of the studied objects were calculated after obtained plasma concentrations of 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil. It was found that the solid dispersion system with Kollidon 17PF has the greatest relative bioavailability from the examined objects; its relative bioavailability to the substance by oral administration was 583 %.Conclusion. The solid dispersion system method increased the bioavailability of 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil. Obtained results confirmed correctness of solid dispersion system selection drug e composition and technology development.

The pharmacokinetic profiling of active compounds is necessary for drug development and application. Approaches to a pharmacokinetic study based on biological markers are alternatives to traditional approaches based on chromatographic methods. The aim of the study was to compare two analytical approaches to pharmacokinetics investigation for an example of sitagliptin in rabbits after one dose oral administration. The method for sitagliptin quantification in rabbit plasma samples based on a correlation between its concentration and dipeptidyl peptidase IV activity was proposed, validated, and applied. The high-performance liquid chromatography (HPLC)-ultraviolet (UV) method was also validated and applied for the same sample analysis. The plasma pharmacokinetics of sitagliptin after oral administration to the rabbits in one dose was characterized after two analytical assays. The close values of the main pharmacokinetic parameters were obtained after two approaches. The nontraditional approach based on correlation of special marker activity and active substance concentration appears to be more sensitive than HPLC-UV. Thus, the sitagliptin concentrations determined by biomarker assay were higher than the lower limit of quantification (LLOQ) for a longer period (more timepoints) than after the HPLC-UV assay. This feature may influence the values of some calculated concentration-dependent (area under the curve [AUC]0-t , etc.) and time-dependent parameters (mean residence time [MRT], T1/2 , etc.). The values of Tmax obtained by the two approaches were similar and adequate for oral drug administration that confirms the correctness of biomarker selection for pharmacokinetics assessment. The obtained results on the example of sitagliptin confirms that the biomarker approach is adequate and applicable for a pharmacokinetics study. Similar approaches may be effective for individual compounds and complex mixtures when it is difficult or impossible to analyze them traditionally by chromatographic methods.