Determination of oxprenolol in human plasma by high-performance liquid chromatography, in comparison with gas chromatography and gas chromatography-mass spectrometry

Optimization of mobile phase in the separation of beta-blockers by HPLC

Beta-blockers are generally determined using high-performance liquid chromatography (HPLC). Previous HPLC separations of beta-blockers have often required a mobile phase containing three components; acetonitrile or methanol to control the retention; buffer to control the ionic strength and pH of the mobile phase; ion-pairing reagent to provide adequate retention of beta-blockers or organic amines as masking agent to reduce peak tailing. Due to the complexity of the mobile phases employed, development of these assays can be a laborious process. Additionally, alkyl sulphonates and organic amines dramatically reduces the life-time reduction of silica based C18 columns. The results of this study demonstrated that the addition of tested alkyl sulphonates and organic amines is not essential for an adequate separation of beta-blockers. In this study, we developed a simple HPLC method for the simultaneous separation of model beta-blockers, atenolol, practolol, metoprolol, oxprenolol and propranolol. Atenolol, practolol, metoprolol, oxprenolol and propranolol adequately separated with high peak symmetries using a mobile phase consisted of methanol/acetonitrile/phosphate buffer (10 mM, pH 3.0) (15:15:70, v/v/v). By altering only the fraction of methanol with respect to acetonitrile, method development becomes a more efficient separation. Furthermore, atenolol, practolol, metoprolol, oxprenolol and propranolol can be detected up to 0.25, 5, 10, 50 and 10 ng ml(-1). In this publication, we present the simultaneous separation of beta-blockers having a wide range of polarity. It is proposed that this new mobile phase, consisting only acetonitrile, methanol and phosphate buffer can be used for the analysis of the several beta-blockers presently in doping control analysis as well as others.

Enantioselective determination of oxprenolol in human plasma using dialysis coupled on-line to reversed-phase chiral liquid chromatography

A fully automated method for the determination of the enantiomers of oxprenolol in human plasma was developed, involving dialysis through a cellulose acetate membrane, clean-up and enrichment of the dialysate on a short precolumn and subsequent chiral liquid chromatographic (LC) analysis. All sample handling operations were executed automatically by a sample processor equipped with a robotic arm (ASTED system). The trace enrichment column (TEC) was packed with octadecylsilica. After conditioning of the TEC with the LC mobile phase and pH 3.0 acetate buffer. After the enrichment step, the analyte was transferred by the LC mobile phase to the analytical column by means of a switching valve. The influence of different parameters of the dialysis process on the recovery of oxprenolol was first investigated using achiral LC conditions. The volume as well as the aspirating and dispensing flow rates of the acceptor solution were the main parameters studied. Oxprenolol was separated on a C18 stationary phase used for the enantioseparation of oxprenolol was a Chiralcel OD-R column which contained cellulose tris (3,5-dimethylphenylcarbamate) coated on silica as chiral selector. The corresponding mobile phase consisted of a mixture of pH 6.0 phosphate buffer containing NaClO4 at 0.45 M concentration and acetonitrile (70:30 v/v). UV detection was performed at 273 nm. The method developed was validated. Recoveries for each enantiomer of oxprenolol were about 80%. The method was found to be linear in the 50-2500 ng ml-1 concentration range (r2 = 0.999 for both enantiomers) and good results with respect to intra- and inter-day reproducibility as well as accuracy were obtained.

Chromatography of beta-adrenergic blocking agents

The determination of beta-blockers has posed pharmaceutical analysts with a variety of problems arising from the essential characteristics of these compounds as bases and the variability of physicochemical properties of individual drugs. Liquid chromatography has become the favoured method of analysis and to a certain extent there is a standardised approach to analysis based on either solvent or solid-phase extraction and reversed-phase high-performance liquid chromatography coupled to fluorescence detection. The analyst must be aware of interactions occurring during extraction stages. All manipulations should be fully evaluated for individual drugs and metabolites prior to use. Other analytical options are chosen for specific or more demanding applications. The use of unmodified silicas for the liquid chromatography of beta-blockers (and other basic drugs) is an example of a potential alternative mode of chromatography. The stereoselectivity of the pharmacology of beta-blockers has spawned a great deal of literature describing the resolution of enantiomers by chromatographic methods. It is envisaged that this area will achieve greater prominence in the future as drug development pursues optical purity. The demand for the availability of enantiomerically pure pharmaceutical preparations will certainly see developments for preparative-scale separations as well as analytical methods and will surely promote developments in new and established methods of chromatography.

High-performance liquid chromatographic determination of beta-adrenoceptor blocking agents in body fluids

Several reports have been published reviewing high-performance liquid chromatographic (HPLC) methods for the determination of beta-adrenoceptor blocking agents (beta-blockers) in biological materials (Flouvat et al., 1981; Mehta, 1983; Marko and Soltés, 1984; Ahnoff et al., 1985; Tkaczyková and Safarík, 1987). Of these, the paper by Mehta (1983) briefly summarizes the interrelationship between physiocochemical properties of beta-blockers with prechromatographic treatment of biological samples, as well as with the HPLC methods used for the determination of 12 beta-adrenoceptor blocking drugs. The work by Ahnoff et al. (1985) concerning the monitoring of cardiovascular drugs also deals with HPLC assays of 18 beta-blockers in plasma. The Appendix to this report presents the great majority of HPLC methods for determining 30 beta-blockers in various body fluids. HPLC methods providing resolution and determination of individual beta-blocker enantiomers have not been included since this topic is being covered by Walle and Walle (1989). The Appendix is just a guide to the methods reviewed for the HPLC determination of parent beta-blockers as well as some of their metabolites co-assayed in various body fluids. It does not include details such as the internal standard, recovery, setting of the detector, limit of determination, etc., given in the individual methods listed. The isolation technique of the drug(s) from the given body fluid represents the main step in the sample work-up procedure. Along with this information, only the type of the HPLC column packing and the detection principle used by each method's developers are given.

Jejunal and ileal absorption of oxprenolol in man: influence of nutrients and digestive secretions on jejunal absorption and systemic availability

1 Study I evaluated the absorption of oxprenolol in the ileum, compared to jejunum, in healthy volunteers by an intestinal perfusion technique. Around 80 mg of drug were delivered as a saline solution directly in the small bowel. 2 Samples taken 30 cm distally to the site of perfusion showed that 63% of perfused oxprenolol was absorbed in the jejunum and 48% in the ileum; the differences were significant. 3 The plasma concentration-time profiles were similar for the two perfusions. The AUC and Cmax values of free and conjugated oxprenolol for the jejunal perfusion were significantly lower than those of ileum. They showed large but consistent intersubject variations in the two treatments. 4 Study II investigated, using the same technique, the influence of nutrients and digestive secretions on jejunal absorption and systemic availability of this drug. A saline (in treatments A and B) or a nutrient (in treatment C) solution containing oxprenolol was perfused into the jejunum below a balloon either inflated (A) or deflated (B and C). 5 The disappearance rate of oxprenolol from the jejunum was unaffected by endogenous secretions. The mean amount of drug absorbed along a 30-cm jejunal segment accounted for 52 (A) and 57% (B) of the total amount perfused. The intestinal absorption rate was markedly increased in the presence of nutrients (mean amount absorbed 96% for C). 6 The change in the rate of disappearance from the intestine had no effect on the systemic availability of oxprenolol (mean AUC values 8740, 8250 and 8020 nmol l-1 h for A, B and C, respectively) or its elimination from plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric and intestinal absorption of oxprenolol in humans

The gastrointestinal absorption of the beta blocker oxprenolol was investigated in four healthy subjects by an intubation technique. Oxprenolol was introduced into the stomach, dissolved in a homogenized meal containing the marker 14C-polyethylene glycol (PEG) 4000. Unlabeled PEG 4000 was perfused during the whole experiment into the duodenum at the ampulla of Vater. Samples of luminal contents were collected at regular intervals over four hours in the stomach, at the angle of Treitz, and 30 cm below this point. Blood was also collected. Oxprenolol was not absorbed in the stomach. About 80% of the drug emptied from the stomach was absorbed in the duodenum, and 80% of that released from the duodenum was absorbed in a 30-cm segment of the jejunum. The amounts absorbed in these two intestinal segments were directly proportional to the amounts delivered. The areas under the plasma concentration-time curves were not related to the amounts absorbed. A single dose of oxprenolol taken with an homogenized meal did not modify the gastric emptying and secretory response.