Doping analysis of beta-blocking drugs using high-performance liquid chromatography

LC and LC-MS/MS studies for the identification and characterization of degradation products of acebutolol

The aim of the present investigation was to demonstrate an approach involving use of liquid chromatography (LC) and liquid chromatography-mass spectrometry (LC-MS) to separate, identify and characterize very small quantities of degradation products (DPs) of acebutolol without their isolation from the reaction mixtures. The drug was subjected to oxidative, hydrolytic, thermal and photolytic stress conditions as per International Conference on Harmonization (ICH) guideline Q1A(R2). Among all the stress conditions the drug was found to be labile in hydrolytic (acidic & basic) and photolytic stress conditions, while it was stable in water-induced hydrolysis, oxidative and thermal stress conditions. A total of four degradation products were formed. A C₁₈ column was employed for the separation of all the DPs on a gradient mode by using high-performance liquid chromatography (HPLC). All the DPs were characterized with the help of their fragmentation pattern and the masses obtained upon LC-MS/MS and MSⁿ analysis. All the hitherto unknown degradation products were identified as 1-(2-(2-hydroxy-3-(isopropylamino)propoxy)-5-(amino)phenyl)ethanone (DP-I), N-(4-(2-hydroxy-3-(isopropylamino)propoxy)-3-acetylphenyl)acrylamide (DP-II), 1-(2-(2-hydroxy-3-(isopropylamino)propoxy)-5-(hydroxymethylamino)phenyl)ethanone (DP-III) and 1-(6-(2-hydroxy-3-(isopropylamino)propoxy)-2,3-dihydro-2-propylbenzo[d]oxazol-5-yl)ethanone (DP-IV). Finally the in-silico carcinogenicity and hepatotoxicity predictions of the drug and all the DPs were performed by using toxicity prediction softwares viz., TOPKAT, LAZAR and Discovery Studio ADMET. The results of in-silico toxicity studies revealed that acebutolol (0.967) and DP-I (0.986) were found to be carcinogenic, while acebutolol (0.490) and DP-IV (0.437) were found to be hepatotoxic.

A minisensor for the rapid screening of atenolol in pharmaceutical preparations based on surface-stabilized bilayer lipid membranes with incorporated DNA

This work describes an electrochemical technique that is suitable for the rapid and sensitive screening of atenolol based on surface-stabilized bilayer lipid membranes (s-BLMs) composed from egg phosphatidylcholine (PC). The interactions of atenolol with s-BLMs produced electrochemical ion current increases that reproducible appeared within a few seconds after the exposure of the membranes to the drug. The current signal increase was related to the concentration of atenolol in bulk solution in the micromolar range. The present lipid film-based sensor provided fast response (i.e. on the order of a few seconds) to alterations of atenolol concentration (20 to 200 micro M) in electrolyte solution. ssDNA incorporated into s-BLMs can interact with atenolol, and decreased the detection limit of this drug by one order of magnitude. The oligomers used were single stranded deoxyribonucleic acids: thymidylic acid icosanucleotide terminated with a C-16 alkyl chain to assist incorporation into s-BLMs (5'-hexadecyl-deoxythymidylic acid icosanucleotide, dT(20)-C(16)). The electrochemical transduction of the interactions of atenolol with s-BLMs was applied in the determination of these compounds in pharmaceutical preparations by using the present minisensor.

Detection of beta-blockers in urine by solid-phase extraction-supercritical fluid extraction and gas chromatography-mass spectrometry

The most convenient way to perform supercritical fluid extraction (SFE) of liquid sample matrices is to combine it with solid-phase extraction (SPE). beta-Blockers from urine were collected on an Empore disc, which was then placed into an extraction cell for derivatization and SFE. SPE recovery was best at pH 10. Effects of temperature, pressure and volume of pyridine on the acetylation and SFE processes were studied. Without acetylation the beta-blockers were not significantly soluble in CO2. SFE temperatures of 70 degree C and 150 degree C together with 200 microliters of acetic anhydride and 400 microliters pyridine gave the best results. With the SPE-SFE-GC-MS method developed here, beta-blockers like oxprenolol, metoprolol and propranolol could easily be detected in urine samples, and the limit of detection (LOD) for these compounds was found to be 20 ng/ml, 30 ng/ml and 40 ng/ml, respectively.

High-performance liquid chromatography with amperometric detection applied to the screening of beta-blockers in human urine

A high-performance liquid chromatographic method with electrochemical detection has been developed for the determination of six beta-blockers: atenolol, nadolol, timolol, metoprolol, oxprenolol, and alprenolol. The chromatographic separation was performed using a mu Bondapack C18 column, a mobile phase of acetonitrile-water (40:60), containing 5 mM KH2PO4/K2HPO4 proved to be optimal at a 1.3 ml/min flow-rate, and a pH of 6.5. The temperature was optimized at 30 +/- 0.2 degrees C. The amperometric detector, equipped with a glassy carbon electrode, was operated at 1300 mV versus Ag/AgCl in the direct current mode. The method was applied to the determination of these compounds at two concentration levels: ppm and ppb (ng/ml), obtaining relative standard deviations lower than 5% at ppm levels and lower than 10% at ppb levels, and quantitation limits ranging from 15 ppb to 500 ppb. The method was applied to the screening of beta-blockers in spiked urine samples, with a total elution time lower than 12 min, obtaining the best recoveries for timolol and metoprolol (never greater than 93%). These recoveries together with the low limits of quantitation achieved, allows its application to doping analysis in human urine.

Screening and determination of beta-blockers, narcotic analgesics and stimulants in urine by high-performance liquid chromatography with column switching

A fast method is described for the screening of eleven beta-blockers, two narcotic analgesics and two stimulants in urine by HPLC with column switching. The urine sample (100 microliters), buffered to pH 9-9.5, is injected onto a short extraction column packed with CN stationary phase. The extraction column is flushed with water for 2.5 min to elute polar matrix components to waste. The retained components are then backflushed by means of a six-port valve onto the ODS analytical column where they are separated. Phosphate buffer pH 3.0 and acetonitrile were used as mobile phase. Gradient elution was applied in the screening method to improve separation. Detection was performed with a diode-array detector at 220, 235 and 300 nm. Recoveries were near 100%, precision was excellent and sensitivity about 0.25 micrograms/l. To speed up the quantitative analysis, the same method but with isocratic elution was successfully applied to the determination of acebutolol and metoprolol in urine samples collected 4 h after administration of the compounds as single doses.