Introduction. Coronavirus disease (COVID-19) is an acute infectious disease caused by SARS-CoV-2 (severe acute respiratory syndrome-related coronavirus 2). Favipiravir is a synthetic prodrug with antiviral activity used for the treatment of COVID-19. There are oral and parenteral dosage forms of favipiravir. Compared with oral administration, parenteral administration has some advantages. Developing a method for the determination of favipiravir in human blood plasma is necessary for performing the analytical part of clinical studies of favipiravir for parenteral administration as an infusion, studying pharmacokinetics, and choosing the optimal dosage of the drug.Aim. The aim of this study is to develop and validate a method for quantitative determination of favipiravir in human plasma by high-performance liquid chromatography with ultraviolet detection (HPLC-UV) for pharmacokinetic studies.Materials and methods. Determination of favipiravir in human plasma by HPLC-UV. The UV detection was set at 323 ± 2 nm. The samples were processed by methanol protein precipitation. Internal standard: raltegravir. Mobile phase: 0.1 % formic acid in water with 0.08 % aqueous ammonia (eluent A), 0.1 % formic acid in acetonitrile with 0.08 % aqueous ammonia (eluent B). Column: Phenomenex Kinetex^®, C18, 150 × 4.6 mm, 5 μm. Analytical range: 0.25–200.00 μg/mL.Results and discussion. This method was validated by selectivity, calibration curve, accuracy, precision, spike recovery, the lower limit of quantification, carry-over effect and stability.Conclusion. We developed and validated the method of quantitative determination of favipiravir in human plasma by HPLC-UV. The analytical range was 0.25–200.00 μg/mL in human plasma. The method could be applied in pharmacokinetics studies of favipiravir.

Introduction.Allaforte® (JSC "Pharmcenter VILAR", Russia) is an antiarrhythmic long-acting drug. The dosage form of the drug Allaforte® provides a decrease in the frequency of taking the drug and also reduces the risk of side effects. It is relevant when taking antiarrhythmic drugs of the IC class. However, the pharmacokinetics of this drug has not been studied on humans. Therefore, it is important to fully study the pharmacokinetics to ensure the maximum efficacy and safety of arrhythmia therapy.Aim.The aim is pharmacokinetics study of long-acting antiarrhythmic drug Allaforte® (JSC "Pharmcenter VILAR", Russia), 25 mg. Materials and methods. Concentration of lappaconitine and its active metabolite N-desacetyllappaconitine in human plasma determinates by high performance liquid chromatography with tandem mass-spectrometry. Pharmacokinetic parameters calculated by R Project 3.5.1 software (package «bear», version 2.8.3-2), originally created by Hsin-ya Lee and Yung-jin Lee, Taiwan.Results and discussion.Pharmacokinetic parameters of lappaconitine and N-desacetyllappaconitine were calculated. Averaged pharmacokinetic profiles (in linear and semi-log scale) of lappaconitine and N-desacetyllappaconitine after single administration under fasting were built. The means of the maximum concentrations (Cmax) determined in the blood plasma of volunteers after single administration Allaforte® are 5.09 ± 4.07 ng/ml for lappaconitine and 11.66 ± 6.21 ng/ml for N-deacetyllappaconitine (Mean ± SD). The peak time of the maximum concentrations (Tmax) is 4.43 ± 3.54 hours for lappaconitine and 4.04 ± 2.18 hours for N-deacetyllappaconitine. The means of the areas under the curve plasma concentration – time from 0 to 48 hours (AUC0-t) and under the curve plasma concentration–time from zero to infinity (AUC0-∞) of Allaforte® is 42.96 ± 34.48 ng ∙ h/ml and 71.24 ± 43.20 ng ∙ h/ml for lappaconitine; 167.42 ± 114.41 ng ∙ h/ml and 189.42 ± 115.20 ng ∙ h/ml for N-deacetyllappaconitine. Allaforte® was eliminated from blood plasma with means of terminal half-life (T1/2) 8.45 ± 5.10 hours for lappaconitine and 9.04 ± 2.57 hours for N-deacetyllappaconitine.Conclusion.Pharmacokinetics study of long-acting antiarrhythmic drug Allaforte® (JSC "Pharmcenter VILAR", Russia) after single administration was researched. Results of the study allows to conduct an effective therapy of arrhythmia by study drug and minimize side effects.

Introduction. Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the SARS-CoV-2 virus (severe acute respiratory syndrome-related coronavirus 2). COVID-19 is now expected to stay with us for many years as a recurring disease. Molnupiravir and favipiravir are oral antiviral drugs with anti-RNA polymerase activity. The Russian Health Ministry has approved molnupiravir and favipiravir for the treatment of COVID-19. The study describes development and validation of high-performance liquid chromatography – tandem mass spectrometry (HPLC-MS/MS) method for the simultaneous determination of β-D-N4-Hydroxycytidine and favipiravir in human blood plasma. The method could be applied in pharmacokinetic study of molnupiravir and favipiravir.Aim. The aim of this study is to develop and validate a HPLC-MS/MS bioanalytical method for the determination of β-D-N4-Hydroxycytidine and favipiravir in human plasma.Materials and methods. The determination of β-D-N4-Hydroxycytidine and favipiravir in human plasma by HPLC-MS/MS. The samples were processed by 0.1 % formic acid in acetonitrile. Internal standard: promethazine. Mobile phase: 0.01 mol/L Ammonium formate buffer solution (Eluent A), 0.1 % formic acid and 0.08 % aqueous ammonia in water/acetonitrile 10 : 90 (Eluent B). Column: Shim-pack GWS C18, 150 × 4.6 mm, 5 μm. Analytical range: 50.00–10000.00 ng/mL for β-D-N4-Hydroxycytidine, 250.00–20000.00 ng/mL for favipiravir in human plasma. Ionization source: electrospray ionization. Detection conditions: 260.00 m/z → 82.10 m/z, 260.00 m/z → 111.00 m/z, 260.00 m/z → 127.95 m/z (β-D-N4-Hydroxycytidine); 156.15 m/z → 65.95 m/z, 156.15 m/z → 85.00 m/z, 156.15 m/z → 113.10 m/z (favipiravir); 285.05 m/z → 198.05 m/z (promethazine).Results and discussion. This method was validated by selectivity, suitability of reference standard, matrix effect, calibration curve, accuracy, precision, spike recovery, the lower limit of quantification, carry-over effect and stability.Conclusion. The HPLC-MS/MS method for quantitative determination of β-D-N4-Hydroxycytidine and favipiravir in human plasma was developed and validated. The analytical range was 50.00–10000.00 ng/mL for β-D-N4-Hydroxycytidine, 250.00–20000.00 ng/mL for favipiravir in human plasma. This method was applied to investigate the pharmacokinetics of molnupiravir and favipiravir.

Introduction. Currently, physicochemical methods of quantification are actively used to determine the content of drugs in biological fluids. High-performance liquid chromatography with various detection methods is particularly widespread. One of the most difficult practical tasks is the chromatographic separation of so-called poorly retained compounds – drug substances poorly retained on the chromatographic column. Valganciclovir and Ganciclovir are among such substances. Aim. The aim of this study is to develop a method for valganciclovir and ganciclovir in human plasma by high performance liquid chromatography with tandem mass-spectrometry (HPLC-MS/MS) for pharmacokinetic studies.Materials and methods. Determination of valganciclovir and ganciclovir in plasma by HPLC-MS/MS. The samples were processed by acetonitrile protein precipitation.Results and discussion. This method was validated by next parameters: selectivity, matrix effect, calibration curve, accuracy, precision, recovery, lower limit of quantification, carry-over and stability.Conclusion. The method of the determination of valganciclovir and ganciclovir in human plasma was developed and validated by HPLC-MS/MS. The linearity in plasma sample was achieved in the concentration range of 5.00–1000.00 ng/ml for valganciclovir and 50.00–10000.00 ng/ml for ganciclovir. Method could be applied to valganciclovir and ganciclovir determination in plasma for PK and BE studies.

Introduction. Favipiravir is one of the most well-known broad-spectrum drugs against many RNA viruses, including the severe acute respiratory syndrome virus 2 [severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)]. Due to its structure, favipiravir is embedded in the RNA of the virus and blocks its further replication in the cell of the human body. Favipiravir is also included in the list of vital and essential medicines, which confirms the importance for Russian healthcare of this drug in the fight against common RNA viruses. We have already published bioanalytical methods for determining favipiravir in human blood plasma by high-performance liquid chromatography with an ultraviolet detector (HPLC–UV) in order to study the pharmacokinetics of favipiravir with parenteral administration (the analytical range of the technique was 0.25–200.00 µg/ ml for the dosage of favipiravir 400 mg in 1 vial of lyophilizate for the preparation of concentrate for the preparation of solution for infusions) and by HPLC with tandem mass-selective detection (HPLC-MS/MS) in order to study the pharmacokinetics of β-D-N4-hydroxycytidine and favipiravir in their joint determination in blood plasma with oral administration (the analytical range of the technique was 250.00–20000.00 ng/ml for the dosage of favipiravir 400 mg in 1 tablet). The expectation of low favipiravir’s concentrations (the dosage of favipiravir in the drugs in question is 200 mg in 1 tablet in this study) and, in this regard, the expansion of the range by reducing the value of the lower limit of quantitative determination (LLOQ) used in this study necessitates the development of another method. Therefore, this study is given the development and validation of a method for determining favipiravir in human blood plasma by HPLC-MS/MS with an analytical range of 50.00–15000.00 ng/ml.Aim. The aim of this study is to develop a method for quantitative determination of favipiravir in human blood plasma by HPLC-MS/MS for further for further researches of pharmacokinetics and bioequivalence of drugs.Materials and methods. In the process of sample preparation, a method of proteins precipitation with methanol was used. A solution labeled with stable isotopes of favipiravir-13C3 was used as an internal standard, the mobile phase was a 0.1 % solution of formic acid in water (eluent A) and methanol (eluent B). Chromatographic column – Phenomenex Kinetex C18, 100×3.0 mm. The determination of favipiravir in human blood plasma was carried out by HPLC using a tandem mass spectrometric detector with a triple quadrupole. The analytical range for favipiravir is 50.00– 15000.00 ng/ml in human blood plasma.Results and discussion. This method was validated by selectivity, calibration curve, accuracy, precision, matrix effect, spike recovery, carry-over effect, the lower limit of quantification and stability.Conclusion. A method of quantitative favipiravir’s determination in human blood plasma by HPLC-MS/MS with a confirmed analytical range of 50.00–15000.00 ng/ml in human blood plasma has been developed and validated. This method allows using it for the analytical part of pharmacokinetics and bioequivalence studies of drugs containing favipiravir in order to expand their range in the domestic pharmaceutical market.

Introduction. Lappaconitine is an alkaloid, contained into Aconitum leucostomum Vorosh. roots and herbs. The alkaloid is indicated to arrhythmia. The lappaconitine drugs are metabolized into eight pharmacologically active substances, but N-desacetyllappaconitine is the most effective. Drugs based on a lappaconitine has narrow therapeutic range and many kinds of side effects. Pharmacokinetics of lappaconitine should be more studied for safety medical use of lappaconitine drugs.Aim. The aim of this study is to develop method for the quantitative determination of lappaconitine and its active metabolite N-desacetyllappaconitine in human plasma and blood by high performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS). Materials and methods. Determination of lappaconitine and N-desacetyllappaconitine in plasma and blood was carried out by HPLC-MS/MS. The samples were processed by acetonitrile protein precipitation.Results and discussion. This method was validated by next parameters: selectivity, matrix effect, calibration curve, accuracy, precision, spike recovery, lower limit of quantification, carry-over effect and stability.Conclusion. The method of the quantitative determination of lappaconitine and N-desacetyllappaconitine in human plasma and blood was developed and validated by HPLC-MS/MS. The analytical range of the was 0.50-50.00 ng/ml for lappaconitine and 0.50-100.00 ng/ml for N-desacetyllappaconitine in biological matrix. Method could be applied to determination of lappaconitine and N-desacetyllappaconitine for PK studies.