Assay of free captopril in human plasma as monobromobimane derivative, using RPLC/(+)ESI/MS/MS: validation aspects and bioequivalence evaluation

Square root law model for the delivery and intestinal absorption of drugs: a case of hydrophilic captopril

The in vivo release and absorption of drugs are dependent on the interplay between many factors related to compound, formulation, and physiological properties. The mathematical models of oral drug absorption attempt to strike a balance between a complete description that takes into consideration as many independent factors as possible, and simple models that operate with fewer parameters, based mainly on critical factors. The latter models are by far more robust and easier to apply to predict the extent and sometimes even the rate of absorption. The present paper attempted to develop a simple model to describe the time course of absorption of the hydrophilic drug captopril (CPT) at the early phases of absorption, with implications mainly in the induction and early stages of achieving its therapeutic effect. As a phenomenological model, the instantaneous release of CPT was considered in the gastrointestinal fluid, leading to a constant drug concentration for a prolonged time, followed by a ‘long path diffusion’ inside the intestinal wall and a very low concentration at the interface intestinal wall-blood. These conditions regarding CPT concentration were translated into initial and boundary mathematical conditions for the diffusion equation in the intestinal wall. The solution of the diffusion equation led in the end to a square root law describing the dependence between the fraction of the drug absorbed and time. The model was successfully applied to data obtained in five bioequivalence studies: three comparing plasma levels achieved after the administration of a single dose of CPT 50 mg, one evaluating CPT pharmacokinetics after a 100 mg dose, and a fifth comparing CPT pharmacokinetics of two fixed-dose combinations of CPT 50 mg and hydrochlorothiazide 25 mg.

Occurrence and Fate of Bisphenol A and its Congeners in Two Wastewater Treatment Plants and Receiving Surface Waters in Romania

The present study investigated the distribution and environmental fate of Bisphenol A (BPA), the 4-hydroxyacetophenone (4-HAP) metabolite, and 5 other bisphenol congeners in 2 municipal wastewater treatment plants (WWTPs) and their receiving rivers in Romania. Accordingly, a new, highly sensitive and accurate solid-phase extraction-liquid chromatography-electrospray ionization-tandem mass spectrometry method was developed and validated. This technique generated low limit of quantitation values: below 2.3 ng/L for surface water and less than 2.4 and 2.7 ng/L for WWTP effluent and influent water. The sum of detected analytes in wastewater was between 1337 and 16 118 ng/L for influent samples and between 15 and 96 ng/L for effluent samples. In surface water, the total of all compounds was somewhere between 34 and 240 ng/L. The highest concentration observed was for BPA in all 3 types of analyzed water (up to 9140 ng/L for influent, as high as 75 ng/L for effluent, and a maximum of 135 ng/L in surface waters). All analyzed samples were free of bisphenols B, C, and F. For all analytes detected in surface water, the concentration values were higher than those determined in the effluent samples, which may be caused by intrinsic contamination of the 2 rivers (Danube and Jiu Rivers). Values of environmental risk coefficients, calculated for both effluents and surface waters, indicated a low ecological risk or no ecological risk for 3 types of organisms (algae, daphnia, and fish). Human risk assessment calculation suggests no risk to human health as a result of the presence of BPA in either of the 2 rivers. Environ Toxicol Chem 2021;40:435-446. © 2020 SETAC.

Derivatization procedures and their analytical performances for HPLC determination in bioanalysis

Derivatization, or chemical structure modification, is often used in bioanalysis performed by liquid chromatography technique in order to enhance detectability or to improve the chromatographic performance for the target analytes. The derivatization process is discussed according to the analytical procedure used to achieve the reaction between the reagent and the target compounds (containing hydroxyl, thiol, amino, carbonyl and carboxyl as the main functional groups involved in derivatization). Important procedures for derivatization used in bioanalysis are in situ or based on extraction processes (liquid-liquid, solid-phase and related techniques) applied to the biomatrix. In the review, chiral, isotope-labeling, hydrophobicity-tailored and post-column derivatizations are also included, based on representative publications in the literature during the last two decades. Examples of derivatization reagents and brief reaction conditions are included, together with some bioanalytical applications and performances (chromatographic conditions, detection limit, stability and sample biomatrix).

In Vitro and In Vivo Evaluation of Different Solid Dosage Forms Containing Captopril

AIM

Comparison of Captopril generic formulations on the Romanian market with the reference formulation Capoten (Bristol Myers Squibb), in terms of in vitro release kinetics of active substance and in vivo pharmacokinetics.

MATERIALS AND METHODS

Dissolution studies were performed using Apparatus 1 (Basket), DT 800H, Erweka, Germany in acidic medium (0.01 N hydrochloric acid) and an agitation speed of 50 rpm. Experiments were run on 12 tablets of each formulation. Quantification of Captopril was achieved by using a spectrophotometric method, λ=205nm. Clinical pharmacokinetics was determined in the frame of four different bioequivalence studies comparing a single dose four different Captopril 50mg generic tablet products to the innovator drug, Capoten 50mg (Bristol Myers Squibb).

RESULTS

Different batches of the reference formulations achieved dissolution profiles of the same form and very closed to each other at all dissolution points. Dissolution profiles of the tested formulations shown similar behavior for all references. Two generic formulations achieved a slower release at early dissolution time points, their release being "diffusion controlled", described by law of Higuchi. In vivo, products proved to be bioequivalent, but variability of space distribution and forms of plasma profiles was much bigger than for the in vitro release curves. Due to very rapid in vitro dissolution, a direct Level A in vitro-in vivo correlation was not possible, but, strangely, the fraction absorbed vs. time clearly followed the same Higuchi law.

CONCLUSION

All the studied formulations achieved more than 85% dissolution after 15 minutes which means that whatever the values of dissolution metrics f1 and f2, formulations behave like a solution and generally should not have therapeutic equivalence problems. Slower dissolution profiles correlates with in vivo absorption being described by the same square root law of Higuchi which describe diffusion controlled transport phenomena.

Development and validation of a simple and sensitive HPLC-UV method for the determination of captopril in human plasma using a new derivatizing reagent 2-naphthyl propiolate

In this study, a simple, sensitive and reliable HPLC-UV method applying rapid sample preparation technique for the determination of captopril in human plasma was developed and validated. The method is based on pre-column derivatization of captopril and 2-propene-1-thiol (internal standard) with a new reagent 2-naphthyl propiolate. Sample clean-up, derivatization and extraction were carried out in two steps, totally less than 30min. The extracts were chromatographed on a C18 column (5μm, 150mm×4.6mmi.d.). The mobile phase consisted of methanol (75%, v/v) and phosphate buffer (25%, pH=8, 0.01M). UV detection was performed at 290nm. To obtain the best reaction yield, the factors that could influence the derivatization process, including the concentration of derivatization reagent, pH of sample solution and temperature were investigated in detail and optimized using Box-Behnken response surface methodology. Under optimized conditions the average extraction recovery of captopril and internal standard were >86%. The achieved lower limit of quantification (LLOQ) was 3ng/mL; the assay exhibited a linear dynamic range of 3-2000ng/mL with correlation coefficient (r(2)) of ≥0.99. The precision was satisfactory in the whole calibration range with RSD of 5.9-12.4% (accuracy: from 97.5% to 93.6%) and of 6.4-12.8% (accuracy: from 97.3% to 95.2%) for intra- and inter-assay, respectively. The method stability was confirmed in a series of experiments including: freeze-thaw, short- and long-term stability testing. Lastly, the developed method was successfully applied to the bioequivalence study of captopril administrated as a single oral dose (50mg) to 12 healthy male volunteers.

Derivatization methods for quantitative bioanalysis by LC–MS/MS

LC with atmospheric pressure ionization MS is essential to a large number of quantitative bioanalyses for a variety of compounds, especially nonvolatile or highly polar compounds. However, in many instances, weak ionization, poor LC retention and instability of certain analytes hinder the development of the LC–MS/MS method. Chemical derivatization has been used for different classes of analytes to improve their ionization efficiency, chromatographic separation and chemical stability. This work presents an overview of chemical derivatization methods that have been applied to the quantitative LC–MS/MS analyses of nine classes of molecules, including aldehydes, amino acids, bisphosphonate drugs, carbohydrates, carboxylic acids, nucleosides and their associated analogs, steroids, thiol-containing compounds and vitamin D metabolites, in biological matrices.

Automated determination of total captopril in urine by liquid chromatography with post-column derivatization coupled to on-line solid phase extraction in a sequential injection manifold

The present study reports a new liquid chromatographic (HPLC) method for the determination of the anti-hypertension drug captopril (CAP) in human urine. After its separation from the sample matrix in a reversed phase HPLC column, CAP reacts with the thiol-selective reagent ethyl-propiolate (EP) in a post-column configuration and the formed thioacrylate derivative is detected at 285 nm. Automated 4-fold preconcentration of the analyte prior to analysis was achieved by an on-line solid phase extraction (SPE) step using a sequential injection (SI) manifold. The Oasis HLB SPE cartridges offered quantitative recoveries and effective sample cleaning by applying a simple SPE protocol. The limits of detection and quantitation were 10 μg L(-1) and 35 μg L(-1) respectively. The percent recoveries for the analysis of human urine samples ranged between 90 and 96% and 95 and 104% using aqueous and matrix matched calibration curves respectively.

Automated tagging of pharmaceutically active thiols under flow conditions using monobromobimane

The thiol-specific derivatization reagent monobromobimane (MBB) is applied--for the first time--under flow conditions. Sequential injection analysis allows the handling of precise volumes of the reagent in the micro-liter range. The effect of the main chemical and instrumental variables was investigated using captopril (CAP), N-acetylcysteine (NAC) and penicillamine (PEN) as representative pharmaceutically active thiols. Previously reported hydrolysis of MBB due to interaction with nucleophilic components of the buffers was avoided kinetically under flow conditions. The proposed analytical scheme is suitable for the fluorimetric determination of thiols at a sampling rate of 36 h(-1).