Fate of beta blockers in aquatic-sediment systems: sorption and biotransformation

The fate of beta blockers (atenolol, acebutolol, bisoprolol, celiprolol, metoprolol, nadolol, pindolol, propranolol, and sotalol) was studied in surface water-sediment systems. A new analytical method was developed to determine the beta blockers in sediments by LC-ESI-tandem MS detection. The relative recoveries in sediments ranged from 89 +/- 7% (acebutolol) to 102 +/- 3% (nadolol) using deuterated surrogate standards. Beta blockers were present with concentrations up to 86 ng/g (bisoprolol) in the sediments of small German streams containing an elevated percentage of treated wastewater. Biotransformation studies and sorption isotherms of the beta blockers were performed with two natural river sediments ("Burgen", "Dausenau") differing in organic carbon content and particle size distribution. Biotransformation of beta blockers in the surface water-sediment systems exhibited a low to high persistence with 90% disappearance (DT(90)) ranging from 0.4-10 d (pindolol, atenolol) to >100 d (sotalol, propranolol or celiprolol). For sorption studies neither NaN(3) addition nor autoclavation led to a complete mass balance of the beta blockers, probably due to biotransformation. Isotherms at 6 h (apparent equilibrium, measuring aqueous and sediment phase) fitted by the Freundlich equation show that sorption of all beta blockers to the Burgen sediment were linear or close to it (i.e., n-values between 0.93 and 1.13), while in the Dausenau sediment the sorptions were slightly non linear (i.e., n-values 0.77-0.91). In river water the sorbed fraction is negligible in comparison to the dissolved fraction. Nevertheless, beta blockers can be detected with concentrations up to 86 ng/g (bisoprolol) in sediments of small streams containing more than 50% treated wastewater.

[Structure and activity of carvedilol]

Unique stereochemistry of the third-generation beta-adrenoblockers is a basis of advantages of the new drugs such as carvedilol. Data on the stereochemistry beta-adrenoblockers and the influence of their optical activity on the pharmacological effects of related drugs are presented. Main steps in the practical invest gation of carvedilol stereoisomers are reviewed. Clinical aspects of the use of carvedilol, representing a racemic mixture of two enantiomers, in the treatment chronic heart failure, arterial hypertension, and coronary heart disease are considered.

Ozonation of metoprolol: elucidation of oxidation pathways and major oxidation products

Oxidation products (OPs) formed during ozonation of metoprolol were identified via liquid chromatography and hybride Qq LIT-MS. Experiments carried out at pH 3 and 8 showed the formation of different OPs, depending on pH. The analysis of samples with and without tertiary butanol (t-BuOH) revealed the influence of OH radical reactions. The OH radical exposure was measured by adding a probe compound (para-chlorobenzoic acid, pCBA). Elucidation of chemical structures confirmed the formation of aldehyde moieties as well as the occurrence of hydroxylation reactions. Several reaction pathways for the formation of the oxidation products are proposed. Analysis of ozonated raw wastewater and the effluent of a municipal wastewater treatment plant spiked with 10 microM metoprolol exhibited a similar OP formation pattern as detected in the reaction system at pH 8 without a radical scavenger. This indicates a significant impact of OH radical exposure on the formation of OPs in real wastewater matrices.

Ozonation of propranolol: formation of oxidation products

Major oxidation products (OPs) of the beta blocker propranolol, formed during ozonation in aqueous solution were identified and oxidation pathways were proposed. Ozonation led to a high number of OPs being formed. In total, chemical structures were elucidated for five different nominal masses (including constitutional isomers, approximately 13 signals), whereas at least eight other OPs and their isomers (approximately 30 signals) remained unidentified. The structural elucidation was performed via liquid chromatography coupled with hybride triple quadrupole with linear ion trap (LC-Qq LIT MS). The primary ozonation product OP-291, was formed by ozone attacking the naphthalene ring, which resulted in the ring-opening and two aldehyde moieties being formed. OP-291 was further oxidized to OP-307, which was then oxidized to OP-281. Experiments were performed at pH 3 and pH 8, as well as in the presence and absence of a radical scavenger. Ozonation of wastewater treatment plant (WWTP) effluents spiked with propranolol (10 microM) led to the same OPs being formed as observed in the experiments with deionized water. Therefore, ozonation of WWTP effluent is resulting in the formation of a high number of OPs with an elevated toxic potential (i.e., formation of aldehydes).

[Comparative enantiomer separation of beta-blockers on polysaccharide derived chiral stationary phases using high performance liquid chromatography with acid or base additive in the mobile phases]

The liquid chromatographic enantiomer separation of beta-blockers on several polysaccharide derived chiral stationary phases (CSPs) (Chiralpak AD, Chiralcel OD, Chiralpak IA and Chiralpak IB) was performed and compared in the normal phase mode using hexane-ethanol in the presence of acid or base additives. The chromatographic conditions were 10% - 30% (v/v) ethanol-hexane containing 0.1% trifluoroacetic acid or triethylamine as the mobile phase at the flow rate of 1.0 mL/min with the detection at 254 nm. The lower enantioselectivities and the shorter retention times on amylose derived CSPs (Chiralpak AD and Chiralpak IA) using the mobile phase with acid additive than those with base additive were shown, except for slightly longer retention times of metoprolol and propranolol on Chiralpak AD. The greater enantioselectivities and the shorter retention times on cellulose derived CSPs (Chiralcel OD and Chiralpak IB) using the mobile phase with acid additive than those with base additive were shown, especially, Chiralcel OD showed dramatically enhanced enantioselectivites using the mobile phase with acidic additive. Also, it was shown that the greater enantiomer separation of beta-blockers on Chiralcel OD was achieved using the mobile phases with the higher concentration acid additive.

A study of the structure of the pindolol based on infrared spectroscopy and natural bond orbital theory

Beta-adrenoceptor-blocking agents (beta-blockers) are on the list of the top selling drugs. Pindolol is a representative of this type of compound, either from the structural point of view, or as reference for comparison of the pharmacokinetic properties of the beta-blockers. A study of the pindolol structure based on infrared spectroscopy and natural bond orbital (NBO) theory is the main aim of the present research. FTIR spectra of the solid pindolol were recorded from 4000 to 400cm(-1), at temperatures between 25 and -170 degrees C. For spectral interpretation, the theoretical vibrational spectra of the conformer present in the solid was obtained at the B3LYP/6-31G* level of theory. NBO analysis of the reference conformer, before and after optimization, was carried out at the same level of theory referred above. Characteristic absorption vibrational bands of the spectra of solid pindolol and of the isolated conformer were identified. Intra- and intermolecular interactions in pindolol were confirmed by the frequency shift of the vibrational modes and by the NBO theory. A detailed molecular picture of pindolol and of its intermolecular interactions was obtained from spectroscopy and NBO theory. The combination of both methods gives a deeper insight into the structure.

Effect of hydrophilic natural gums in formulation of oral-controlled release matrix tablets of propranolol hydrochloride

In order to develop a controlled delivery of highly water-soluble propranolol hydrochloride (PPHCl) using hydrophilic natural gums (xanthan gum [X] and locust bean gum [LBG]) as cost-effective, nontoxic, easily available. The granules of PPHCl were prepared by wet granulation method using a different ratios drug: gum ratios of X, LBG and XLBG(X and LBG in 1:1 ratios). To increase the flowability and compressibility of the granules, and to prevent its adhesion to punch and die, magnesium stearate and talc were added to the granules in 1:2 ratios before punching. The tablet was analysed to determine hardness, friability, % assay and invitro release study was carried out. The release of PPHCl from a gelatinous swollen mass, which controls the diffusion of drug molecules through the polymeric material into aqueous medium. The XLBG matrice shows precise controlled release than the X and LBG matrice because of burst effect and fast release in case of X and LBG matrice respectively and there was no chemical interaction between drug and polymer in XLBG formulation as confirmed by FTIR studies. First pass effect of PPHCl can be avoided by these formulations. Matrices with XLBG show zero-order release via swelling, diffusion and relaxation mechanism. The XLBG matrice leads to more precise result than X and LBG alone by the utilization of synergistic interaction between two biopolymers and uniformity in the hydration layer in dissolution media. However, according to the similarity factor (f(2)) XLBG3 were the most similar formulations to Lol-SR as the reference standard.

In-vitro relationship between protein-binding and free drug concentrations of a water-soluble selective beta-adrenoreceptor antagonist (atenolol) and its interaction with arsenic

The degree of binding of a drug to plasma proteins has a marked effect on its distribution, elimination, and pharmacological effect since only the unbound fraction is available for distribution into extra-vascular space. The protein-binding of atenolol was measured by equilibrium dialysis in the bovine serum albumin (BSA). Free atenolol concentration was increased due to addition of arsenic which reduced the binding of the compounds to BSA. During concurrent administration, arsenic displaced atenolol from its high-affinity binding Site I, and free concentration of atenolol increased from 4.286 +/- 0.629% and 5.953 +/- 0.605% to 82.153 +/- 1.924% and 85.486 +/- 1.158% in absence and presence of Site I probe respectively. Thus, it can be suggested that arsenic displaced atenolol from its binding site resulting in an increase of the free atenolol concentration in plasma.

Fabrication of modified release tablet formulation of metoprolol succinate using hydroxypropyl methylcellulose and xanthan gum

The present investigation was undertaken to fabricate modified release tablet of metoprolol succinate using hydroxypropyl methylcellulose (HPMC) and xanthan gum as a matrixing agent. A 3(2) full factorial design was employed for the optimization of formulation. The percentage drug released at a given time (Y (60), Y (240) and Y (720)) and the time required for a given percentage of drug to be released (t (50%)) were selected as dependent variables. The in vitro drug dissolution study was carried out in pH 6.8 phosphate buffer employing paddle rotated at 50 rpm. The similarity factor (f (2)) was calculated for selection of best batch considering mean in vitro dissolution data of Seloken XL as a reference profile. It is concluded that the desired drug release pattern can be obtained by using a proper combination of HPMC (high gelling ability) and xanthan gum (quick gelling tendency). The economy of xanthan gum and faster hydration rate favors its use in modified release tablets. The matrix integrity during dissolution testing was maintained by using hydroxypropyl methylcellulose.

Application of the statistical methods in systematic structure-activity relationship analysis of thiazole, benzothiazole and tetrahydroisoquinoline derivatives with biological activity

The procedure of initial studies to evaluate usefulness of the collected data for performing efficient QSAR analysis of any group of pharmacologically active substances was worked out. Structure-Activity Relationship (SAR) study on the thiazole derivatives with H1-antihistamine activity, the benzothiazole derivatives with H3-antihistamine activity and tetrahydroisoquinoline (TIQ) derivatives with beta 2-adrenolytic activity, was performed by means of Factor Analysis (FA) and Regression Analysis (RA). The potential drug forms (neutral or ionic) in the particular physiological environment (pH) were used to examine the actual properties of the drug in its action place. It was determined based on their pKa values. The usefulness of the group cases selected for QSAR studies was evaluated, based on the relationship between their structural variability and the variability of their specific biological activity.

Photolysis of beta-blockers in environmental waters

Many drugs such as beta-blockers have been shown to occur in aquatic environments. Even if adequate ecotoxicity data are not available, it is of primary importance to get informations about their fate in environmental waters, particularly about their photofate in sewage treatment plant effluents (STP). The main difficulties when studying pharmaceutical photochemical behaviour in environmental waters, are linked to the very low environmentally relevant concentrations (ng L(-1) to microg L(-1)) which can generate problems in terms of analytical sensitivity. Moreover, the complexity of environmental matrices can modify micropollutants degradation kinetics. The photodegradation of beta-blockers has been compared at two concentration levels (10 microg L(-1) and 10 mg L(-1)) and in two different matrices (pure water and STP effluent). It has been shown that the concentration does not influence beta-blockers degradation pathways, thus allowing the identification of degradation compounds using the 10 mg L(-1) solutions. Although environmental waters speed up the degradation process, the same photoproducts were appeared in both matrices. Using LC-MS/MS, hydroxyl radical additions have been identified as an important degradation pathway for especially pindolol, propranolol and timolol, leading to several positional isomers, corresponding to mono-, di- or tri-hydroxylations. Kinetics of appearance/disappearance of these photoproducts have been studied in STP effluents.

Use of Natural Gums and Cellulose Derivatives in Production of Sustained Release Metoprolol Tablets

Metoprolol tartrate sustained-release tablets (100 mg) were prepared using xanthan/guar gums and also hydroxypropyl methyl cellulose (HPMC) carboxymethyl-Cellulose (CMC) polymers by direct compression method. Physical characteristics of the tablets and water uptake in addition to their dissolution profiles were compared with standard (Lopressor SR) tablets. Dissolution test was performed in the phosphate buffer solution (pH 6.8) and the samples were analyzed spectrophotometerically in 275.7 nm. Dissolution studies showed that formulations containing 100 and 80% of HPMC, 100% of guar, and 20% of xanthan followed the Higuchi model, while those containing 60 and 40% HPMC and 100 and 80% xanthan followed a zero-order model. The tablets with 40% xanthen followed a Hixon-Crowell model. In cellulose derivatives the highest MDT and dissolution efficiency until 8 hr (DE8%) belonged to tablets with 40% HPMC, increasing the amount of CMC decreased the drug release rate, and formulations containing 60 and 40% of HPMC had the USP dissolution standards. While, in the gum formulations, the highest mean dissolution time and the lowest DE(8)% belonged to tablets with 100% xanthan, increasing the xanthan decreased the release rate of metoprolol, and formulations containing 80 and 100% xanthan had the USP dissolution standards. Results showed that natural gums are suitable for production of sustained-release tablets of metoprolol.

Preparation and Characterization of Metoprolol Controlled-Release Solid Dispersions

In recent years, great attention has been paid to using solid dispersions to make sustained-release drugs. The objective of this study is to produce sustained-release systems of metoprolol tartrate using solid dispersion techniques and to evaluate their physicochemical characteristics. The solid dispersions were produced by melting and solvent methods, containing 7%, 15%, or 25% of the drug and different ratios of Eudragit RLPO and RSPO in ratios of 0:10, 3:7, 5:5, 7:3, and 10:0. Drug release profiles were determined by USP XXIII rotating paddle method in phosphate buffer solution (pH 6.8). XRD, DSC, IR, and microscopic observations were performed to evaluate the physical characteristics of solid dispersions. Results showed that the drug release from dispersions was at a slower rate than pure drug and physical mixtures. Moreover, the formulations containing greater ratios of Eudragit RSPO showed slower release rates and smaller DE8% but larger mean dissolution time than those containing greater ratios of Eudragit RLPO. Dispersions with particle size of less than 100 microm containing 7% of metoprolol and Eudragit RL:RS 5:5 (solvent method) and those with the ratio of 3:7 (melting method) had similar release pattern to Lopressor sustained-release tablets by zero-order and Higuchi kinetics, respectively.

Radical Crosslinked Albumin Microspheres as Potential Drug Delivery Systems: Preparation and In Vitro Studies

This article reports on the preparation of acryloylated bovine serum albumin microspheres and the evaluation of their employment in drug delivery areas. The influence of preparation parameters on albumin microspheres and the chemicophysical properties of loaded drugs were investigated. In particular, we focussed on acylation albumin degree and the amount of acryloylated albumin against comonomer in the polymerization step. Finally the release profile took into consideration the interaction drug-matrix, the fuctionalization degree of albumin, and the water affinity of matrix.

Effect of Penetration Enhancers on the Transdermal Delivery of Bupranolol Through Rat Skin

Bupranolol (BPL) is a suitable drug candidate for transdermal drug delivery system development based on its favorable physicochemical and pharmacokinetic properties. The effect of different penetration enhancers on the permeation of BPL across rat skin was studied using side-by-side diffusion cells. 2-Pyrrolidone (PY), 1-methyl-2-pyrrolidone (MPY), and propylene glycol (PG) at various concentrations were used as penetration enhancers along with 0.4% w/v aqueous suspension of BPL. Menthol at different concentrations in isopropanol-water (6:4) mixture also was used as an enhancer wherein BPL at 0.4% w/v was completely solubilized. Skin pretreatment studies were carried out with all the above enhancers to understand their role in the penetration enhancement effect. PY and MPY at 5% w/v concentrations increased the permeation of BPL by 3.8- and 2.4-fold, respectively, versus control (p < .01). PG at 10% and 30 w/v concentrations increased the flux of BPL by 2.5- and 5.0-fold, respectively, versus control (p < .001). Menthol at 2% w/v concentration increased the flux of BPL by 3.8-fold (p < .01) and further increase in menthol concentration significantly decreased the flux of BPL. Overall, pyrrolidones and menthol at low concentrations (5% w/v or less) and PG at 30% w/v concentration were effective as penetration enhancers for BPL.

Environmentally Responsive Ophthalmic Gel Formulation of Carteolol Hydrochloride

Environmentally responsive gel formulation for ocular controlled delivery of carteolol hydrochloride (HCl) was developed in an attempt to improve ocular bioavailability and hence decrease its systemic absorption and side effects. The viscosity and the ability of the prepared formulations to deliver carteolol HCl in vitro and in vivo were monitored and compared with an aqueous commercial solution. The effect of polymer concentration and drug concentration on the in vitro release of carteolol HCl was examined. Gelrite formulations showed pseudoplastic behavior with thixotropic characteristics and the viscosity of the prepared systems increased as the concentration of the polymer increased. At fixed drug concentrations, as the Gelrite concentration increased, the drug release decreased. At fixed polymer concentrations, as the drug concentration increased the release of drug increased. Gelrite formulation (0.4% w/w) containing 1% drug showed significantly improved bioavailability compared with the commercial aqueous solution (Arteoptic 1%). The developed in situ gel formulation showed potential for use as delivery systems with superior ocular bioavailability of carteolol HCl.

Stability of Atenolol, Acebutolol and Propranolol in Acidic Environment Depending on its Diversified Polarity

The main objective of this research was to investigate the relationship between the polarity of atenolol, acebutolol, and propranolol described by logP and kinetic and thermodynamic parameters characterizing their degradation process in acidic solution. Hydrolysis was carried out in hydrochloric acid at molal concentrations of 0.1 mol/L, 0.5 mol/L, and 1 mol/L for 2 hr at 40 degrees C, 60 degrees C, and 90 degrees C. Chromatographic-densitometric method was used for the determination of drugs under investigation. The identification of degradation products was carried out by using 1H NMR. The degradation processes that occurred in drugs under investigation are described with kinetic parameters (k, t0.1, and t0.5) and energy of activation (Ea). It has been found that the stability of drugs increases toward lipophilic propranolol in the assumed experimental model. The rate constants k decrease, contrary to t0.1, t0.5, and Ea, which vary comparably to logP, thus increasing from the most hydrophilic atenolol, through acebutolol, of lower polarity, to the most lipophilic propranolol. This study demonstrated that the stability of chosen beta-adrenergic blocking agents increases with their lipophilicity.

Using an Experimental Design to Identify and Quantify the Effects of Environment Related Test Parameters on the In Vitro Mucoadhesivity Testing of a Propanolol Buccal Tablet

This study sought to identify and quantify the effects of environmental test parameters on the mucoadhesivity of a propranolol tablet. Their effects on Maximum Detachment Force (MDF) measurements were evaluated using a Box-Behnken design matrix. Prehydration time (PT) had a statistically significant negative main effect while contact force (CF) had no significant effect on in vitro MDF measurements. While contact time (CT) had no significant main or quadratic effects, it had a positive interaction effect with PT. The mathematical model was statistically validated and a PT of 3.5 min and a CT of 5 min was proposed for mucoadhesion testing by the tensile method during formulation optimization.

Structure of a beta1-adrenergic G-protein-coupled receptor

G-protein-coupled receptors have a major role in transmembrane signalling in most eukaryotes and many are important drug targets. Here we report the 2.7 A resolution crystal structure of a beta(1)-adrenergic receptor in complex with the high-affinity antagonist cyanopindolol. The modified turkey (Meleagris gallopavo) receptor was selected to be in its antagonist conformation and its thermostability improved by earlier limited mutagenesis. The ligand-binding pocket comprises 15 side chains from amino acid residues in 4 transmembrane alpha-helices and extracellular loop 2. This loop defines the entrance of the ligand-binding pocket and is stabilized by two disulphide bonds and a sodium ion. Binding of cyanopindolol to the beta(1)-adrenergic receptor and binding of carazolol to the beta(2)-adrenergic receptor involve similar interactions. A short well-defined helix in cytoplasmic loop 2, not observed in either rhodopsin or the beta(2)-adrenergic receptor, directly interacts by means of a tyrosine with the highly conserved DRY motif at the end of helix 3 that is essential for receptor activation.

[Screening, quantification and confirmation of beta-blockers in urine using gas chromatography-mass spectrometry]

A method was developed to perform the screening, quantification and confirmation of the five beta-blockers, propranolol, carteolol, bisoprolol, esmolol, and sotalol, in human urine using gas chromatography-mass spectrometry (GC-MS). In sample preparation, conjugated and unconjugated beta-blockers in urine were extracted separately, and the extracts were combined. The extracts were derivatized with N-methyl-N-trimethylsilyl-trifluoroacetamide (MSTFA) and N-methyl-bis(trifluoroacetamide) (MBTFA). The optimal conditions of GC-MS were established, and the progresses of screening by selected ion monitoring (SIM) mode and confirmation by full scan (SCAN) mode were completed. At last, the quantification curves of the five beta-blockers in spiked urine were established by SIM mode. The limits of detection were 0.2 -1.0 ng/mL. Overall recoveries were 70.5% - 103.4%, and the relative standard deviations were lower than 15%. In addition, the method was successfully applied to the analysis of the positive urine of propranolol, and the urinary excretion curve was also established accordingly. It is significant to prohibit the abuse of beta-blockers in doping control.

In vitro permeation of carvedilol through porcine skin: effect of vehicles and penetration enhancers

This investigation studied the effect of vehicles on the in vitro permeation of carvedilol from saturated solutions across porcine skin and selected appropriate penetration enhancers. Labrasol, Transcutol, polyethylene glycol 400, propylene glycol, ethanol, oleic acid, isopropyl myristate, and phosphate buffered saline (pH 7.4) containing 40% v/v polyethylene glycol 400 as control, were used as vehicles; limonene, carvone, camphor, menthol, Transcutol, and Labrasol at 5% w/v concentrations were used as penetration enhancers. Skin permeation studies were conducted in Franz diffusion cells using excised porcine ear skin. Solubility was highest (369.13 mg/mL) in Transcutol, whereas isopropyl myristate showed the lowest solubility (0.79 mg/mL) among all the vehicles. The flux of carvedilol from Transcutol, Labrasol, polyethylene glycol 400, ethanol, and oleic acid was 10.5, 8.6, 4.2, 2.9, and 1.5 times higher, respectively, than that observed with control. The flux obtained using Transcutol was significantly higher (P < 0.05) than the flux obtained using the other vehicles. However, the flux values of carvedilol using isopropyl myristate (P < 0.01) and propylene glycol (P < 0.05) were significantly lower than that of the control. Solutions containing 5% w/v camphor showed maximum permeation (232.54 microg) in 24 h with a flux of 3.19 microg/cm2/h, which was significantly different (P < 0.05) than the flux obtained using other permeation enhancers. The control sample showed lowest permeation (30.50 microg), with a flux of 0.33 microg/cm2/h. The flux of carvedilol from the solutions containing 5% w/v camphor, limonene, Transcutol, carvone, Labrasol, and menthol were 9.7, 7.6, 7.6, 6.3, 4.7, and 2.3 times higher, respectively, than that observed using the control. The present study suggests that Transcutol, Labrasol, and polyethylene glycol 400 may be used as potential vehicles and camphor, limonene, and Transcutol at a 5% w/v level as penetration enhancers.

Design and in vivo evaluation of carvedilol buccal mucoadhesive patches

The buccal region offers an attractive route of administration for systemic drug delivery. Carvedilol (dose, 3.125-25 mg) is beta-adrenergic antagonist. Its oral bioavailability is 25-35% because of first pass metabolism. Buccal absorption studies of a carvedilol solution in human volunteers showed 32.86% drug absorption. FTIR and UV spectroscopic methods revealed that there was no interaction between carvedilol and polymers. Carvedilol patches were prepared using HPMC, carbopol 934, eudragit RS 100, and ethylcellulose. The patches were evaluated for their thickness uniformity, folding endurance, weight uniformity, content uniformity, swelling behaviour, tensile strength, and surface pH. In vitro release studies were conducted for carvedilol-loaded patches in phosphate buffer (pH, 6.6) solution. Patches exhibited drug release in the range of 86.26 to 98.32% in 90 min. Data of in vitro release from patches were fit to different equations and kinetic models to explain release profiles. Kinetic models used were zero and first-order equations, Hixon-Crowell, Higuchi, and Korsmeyer-Peppas models. In vivo drug release studies in rabbits showed 90.85% of drug release from HPMC-carbopol patch while it was 74.63 to 88.02% within 90 min in human volunteers. Good correlation among in vitro release and in vivo release of carvedilol was observed.

Ozonation of reverse osmosis concentrate: kinetics and efficiency of beta blocker oxidation

Reverse osmosis (RO) concentrate samples were obtained from a RO-membrane system that uses effluents of wastewater treatment plants (WWTP) as feed water for the production of drinking water. A number of different pharmaceuticals (e.g. antibiotics, contrast media, beta blockers) were found in the WWTP effluent as well as in the RO-concentrate. Overall, a concentration factor (feed:concentrate) of approximately 3-4 was measured. Beta blockers (acebutolol, atenolol, bisoprolol, celiprolol, metoprolol, propranolol, timolol) were found in the range of low ng/L to low microg/L. Because metoprolol and propranolol are classified as potentially toxic to aquatic organisms and all beta blocker molecules have moieties, which are reactive towards ozone (amine groups, activated aromatic rings), it was tested whether ozonation can be applied for their mitigation. Rate constants for the reaction of acebutolol, atenolol, metoprolol and propranolol with ozone and OH radicals were determined. At pH 7 acebutolol, atenolol and metoprolol react with ozone with an apparent second-order rate constant k(O)(3) of about 2,000 M(-1)s(-1), whereas propranolol reacts with approximately 10(5)M(-1)s(-1). The rate constants for the reaction of the selected compounds with OH radicals were determined to be 0.5-1.0 x 10(10)M(-1)s(-1). Experiments with RO concentrate showed that an ozone dose of only 5mg/L resulted in a quantitative removal of propranolol in 0.8s and 10mg O(3)/L oxidized 70% of metoprolol in only 1.2s. Tests with chlorinated and non-chlorinated WWTP effluent showed an increase of ozone stability but a decrease of hydroxyl radical exposure in the samples after chlorination. This may shift the oxidation processes towards direct ozone reactions and favor the degradation of compounds with high k(O)(3).

Comparative study of propranolol hydrochloride release from matrix tablets with KollidonSR or hydroxy propyl methyl cellulose

The release of propranolol hydrochloride from matrix tablets with hydroxy propyl methyl cellulose (HPMC K15M) or KollidonSR at different concentrations was investigated with a view to developing twice daily sustained release dosage form. A hydrophilic matrix-based tablet using different concentrations of HPMC K15M or KollidonSR was developed using direct compression technique to contain 80 mg of propranolol hydrochloride. The resulting matrix tablets prepared with HPMC K15M or KollidonSR fulfilled all the official requirements of tablet dosage forms. Formulations were evaluated for the release of propranolol hydrochloride over a period of 12 h in pH 6.8 phosphate buffer using USP type II dissolution apparatus. Propranolol hydrochloride and pure KollidonSR or HPMC K15M compatibility interactions was investigated by using Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). FTIR spectroscopic and DSC studies revealed that there was no well defined chemical interaction between propranolol hydrochloride with KollidonSR or HPMC K15M. Tablets were exposed to 40 degrees C/75% of RH in open disc for stability. The in vitro drug release study revealed that HPMC K15 at a concentration of 40% of the dosage form weight was able to control the release of propranolol hydrochloride for 12 h, exhibit non-Fickian diffusion with first-order release kinetics where as at 40% KollidonSR same dosage forms show zero-order release kinetics. In conclusion, the in vitro release profile and the mathematical models indicate that release of propranolol hydrochloride can be effectively controlled from a single tablet using HPMC K15M or KollidonSR matrix system.

S-metoprolol: the 2008 clinical review

Metoprolol is a widely used cardioselective beta-blocker. However, like all other beta-blockers it is also a racemic mixture of R- and S- isomers. The beta 1 blocking activity (cardioselectivity) of metoprolol resides in S-isomer while R-isomer exhibits beta 2 blocking activity. As both these isomers have different pharmacological properties, racemic metoprolol can be considered a combination of two different drugs in a fixed 1:1 ratio. The needless administration of the non beta-blocking R-enantiomer that makes up 50% of racemate actually puts the patient at an increased risk of side-effects, drug interactions and loss of cardioselectivity with up-titration of dosing. Clinical experience with chirally pure S-metoprolol at half the dose of racemate has shown it to be as effective as racemate in the treatment of patients with hypertension and angina. S-metoprolol has been shown to be effective and well-tolerated in patients with coexisting diabetes, COPD, and hyperlipidaemia. This confirms higher cardioselectivity of S-metoprolol in clinical settings. Less interaction potential of S-metoprolol compared to R-isomer further makes it a sensible choice in patients taking CYP2D6 inhibitors or in patients with heart failure or hepatic insufficiency. This article reviews differing properties of two isomers of metoprolol with focus on clinical experience with S-metoprolol.