Biphasic effect of local anesthetic and beta-blocker heptacaine on fluidity of phosphatidylcholine bilayers as detected by ESR spin probe method

Heptacaine (1), the monohydrochloride of [2-(heptyl-oxy)phenyl]-2-(1-piperidinyl)ethyl ester of carbamic acid, exerts a biphasic effect on the fluidity of egg yolk phosphatidylcholine (EYPC) model membranes as detected by the methyl esters of stearic acid spin probes with the paramagnetic doxyl group bound to the C-12 or C-16. The fluidity initially increases with an increase in the molar ratio of 1:EYPC, but a molar ratios above 1:EYPC = 0.5 a decrease of fluidity has been observed.

Protective effects of beta-blockers against 2,2'-azobis(2-amidinopropane)-dihydrochloride-induced damage

The protective effects of beta-blockers against 2,2'-azobis(2- amidinopropane)-dihydrochloride (AAPH)-induced damage were investigated. With the exception of pindolol, none of the beta-blockers tested inhibited arachidonate peroxidation induced by AAPH in the absence of iron. In contrast, ADP-Fe(3+)- and NADPH-dependent microsomal lipid peroxidation was inhibited by all the beta-blockers tested, although the inhibitory effects of atenolol and metoprolol were very slight. Oxidation of tryptophan residues in bovine serum albumin (BSA) induced by AAPH was strongly inhibited by pindolol and propranolol but not by atenolol or metoprolol. All the beta-blockers tested, however, inhibited AAPH-induced carbonyl formation of BSA. Furthermore, all the beta-blockers tested also strongly inhibited the deoxyribose degradation induced by AAPH, suggesting that these agents act as hydroxyl radical scavengers to inhibit carbonyl formation. DNA strand scission was induced by AAPH in the absence or presence of O2. Only pindolol strongly inhibited the DNA damage in the absence of O2. In the presence of O2, however, all the beta-blockers tested effectively prevented the DNA damage. These results suggested that the hydroxyl radicals produced from AAPH damaged DNA and, that beta-blockers might act as hydroxyl radical scavengers to protect DNA against the AAPH-induced oxidative damage.

High-performance liquid chromatographic analysis of pindolol enantiomers in human serum and urine using a reversed-phase cellulose-based chiral column

Simple, sensitive and reliable high-performance liquid chromatographic methods are reported for the determination of pindolol enantiomers in human serum and urine. The methods involved a solid-phase extraction of serum and a direct injection of urine samples. The separation of R(+)- and S(-)-pindolol was accomplished on a reversed-phase cellulose-based chiral column with a mobile phase of 40:60 (v/v) acetonitrile-0.3 M aqueous sodium perchlorate at a flow-rate of 0.5 ml/min. The detection was achieved by monitoring the fluorescence emission of pindolol enantiomers at 310 nm with excitation at 270 nm. The limits of detection were 1.2 ng/ml of R(+)- and 4.3 ng/ml of S(-)-pindolol in serum, and 21 ng/ml of R(+)- and 76 ng/ml of S(-)-pindolol in urine. The external standard method was used for quantitation. The methods have been applied to the analysis of human serum and urine samples in a pharmacokinetic study.

Different actions between pindolol and propranolol on the ionic currents in spontaneously beating rabbit sino-atrial node cells

Electrophysiological effects of beta-adrenoceptor blocking drugs (pindolol and propranolol) on the action potentials (APs) and the membrane currents in spontaneously beating rabbit sino-atrial (SA) node cells were examined by the two-microelectrode voltage-clamp technique. Cumulative administrations of both blocking drugs (10(-7)-10(-6) M) prolonged the AP duration (APD) and caused a negative chronotropic effect in a concentration-dependent manner. Propranolol exhibited stronger responses than pindolol. At 10(-6) M, propranolol depolarized the maximum diastolic potential (MDP) and pindolol decreased the maximum rate of depolarization significantly, but the drugs had little or no effect on the AP amplitude (APA). In voltage-clamp experiments, both blockers (10(-7)-10(-6) M) inhibited the slow inward and the time-dependent outward currents in a concentration-dependent manner. Holding potential was -40 mV. The hyperpolarization-activated inward current was not affected by pindolol, but it was concentration-dependently inhibited by propranolol. The inactivation curve of Isi was not modified by either pindolol or propranolol. The activation curve of IK was unaffected by pindolol, but was shifted by propranolol 10(-6) M by approximately 11 mV in the depolarizing direction. These results indicate that both beta-adrenoceptor blocking drugs (pindolol and propranolol) inhibit the slow inward and the time-dependent outward currents, but produce different actions on the hyperpolarization-activated inward current and the activation kinetic of IK due to their pharmacological properties, thereby resulting in difference in decrease in the spontaneous activity of rabbit SA node cells.

Interaction between bile salts and beta-adrenoceptor antagonists

The interactions between beta-adrenoceptor antagonists and bile salts were investigated by microcalorimetry. Nadolol and oxprenolol interactions with dihydroxy salts could be described by a 1:1 interaction model with the thermodynamic parameters indicating that the drugs were incorporated within the bile salt aggregates. This weak interaction was primarily hydrophobic although electrostatic attraction also played a role. Atenolol and metoprolol did not interact with the dihydroxy salts. None of the compounds interacted with trihydroxy bile salts or with salts below their aggregation concentration. Phase separation resulted when propranolol and alprenolol were present in dihydroxy salt solutions above a certain concentration with the interaction being of a hydrophobic and electrostatic nature. The implications of these results on in-vivo drug absorption are discussed.

Drug delivery studies in Caco-2 monolayers. Synthesis, hydrolysis, and transport of O-cyclopropane carboxylic acid ester prodrugs of various beta-blocking agents

A series of O-cyclopropane carboxylic acid ester prodrugs of various beta-blocking agents was synthesized. All prodrugs were hydrolyzed to give their parent compounds in aqueous phosphate buffer of pH 7.4 and in 80% human plasma. The half-lives in buffer solutions varied from 4 hours for the timolol prodrug to about 1 day for the prodrug of alprenolol. In human plasma the half-lives were shorter, ranging from 1 to 7 hours. The formation of the O-cyclopropane carboxylic acid ester derivatives significantly increased the lipophilicities of the beta-blockers as measured by the distribution coefficient between n-octanol and aqueous phosphate buffer of pH 7.4. To characterize the biomembrane permeability characteristics of the beta-blockers, transport properties across Caco-2 cell monolayers were investigated. An increase in lipophilicity resulted in a higher permeability of the prodrugs as compared to the parent compounds. Hence, acebutolol experienced an increment of a factor 17 on the apparent permeability coefficient, Papp, whereas Papp for the more lipophilic drug propranolol was increased by a factor of only 1.26. Some conversion of the prodrugs to their parent compounds was observed during the transport and appeared to be due to enzymatic intracellular metabolism.

Evaluation of the Salivette as sampling device for monitoring beta-adrenoceptor blocking drugs in saliva

The Salivette was evaluated with a range of racemic beta-adrenoceptor blocking drugs with different lipophilicity. Recovery from the Salivette appeared to be independent of the stereochemical configuration of the drugs but a significant loss of drug due to the Salivette was observed for all tested drugs. The performance of the method, in terms of accuracy and precision, fitted well within the generally accepted criteria for validation, except near the limit of quantification. The Salivette is successfully used for quantitating salivary beta-blocking drugs.

Synthesis and beta-adrenergic activity of new completely aliphatic 3-(methyleneaminoxy)propanolamine derivatives

In a previous paper, it had been found that completely aliphatic 3-(methylene aminoxy)propanolamine derivatives showed a good beta-blocking adrenergic activity directed prevalently towards beta 2-tracheal receptors. In an attempt to change the beta-adrenergic properties of these compounds from antagonist to agonist, while still retaining the beta 2-selectivity, a series of new completely aliphatic 3-(methyleneaminoxy)propanolamine derivatives were designed in which either a hydroxylic or a methoxylic group was present on the aliphatic portion linked to the oximic carbon. The synthesis of the new compounds and their beta-adrenergic activity, evaluated by means of functional tests on isolated preparations, are described and discussed; the results obtained are then rationalised on the basis of their conformational and reactivity characteristics, determined by means of theoretical methods.

Stability of esmolol hydrochloride in intravenous solutions

The stability of esmolol hydrochloride in a variety of i.v. solutions was studied. Solutions of esmolol hydrochloride 10 mg/mL were prepared separately in 0.45% sodium chloride injection, 0.9% sodium chloride injection, 5% dextrose injection, 5% dextrose and 0.45% sodium chloride injection, 5% dextrose and 0.9% sodium chloride injection, 5% dextrose with lactated Ringer's injection, lactated Ringer's injection, 5% sodium bicarbonate injection, and 5% dextrose injection with potassium chloride 40 meq/L. One glass and one polyvinyl chloride container of each solution (except glass only in the case of the solution in 5% sodium bicarbonate injection) were stored in the dark at 5 degrees C, under ambient room light at 23-27 degrees C, in the dark at 40 degrees C, and under intense light at 25-30 degrees C. At storage intervals up to 168 hours, samples were tested for esmolol hydrochloride concentration by high-performance liquid chromatography. Optical density and pH were also measured. Esmolol hydrochloride was stable in the various i.v. fluids for at least 168 hours when stored at 5 degrees C or 23-27 degrees C, for at least 24 hours when stored under intense light, and, with one exception, for at least 48 hours when stored at 40 degrees C. When mixed with 5% sodium bicarbonate injection, the drug was stable for only about 24 hours at 40 degrees C. There were no substantial changes in optical density or pH. The type of container had no effect on stability. With one exception, esmolol hydrochloride was stable in all the i.v. solutions under all the conditions tested.

Assessment of impact of physico-chemical drug properties on monitoring drug levels by micellar electrokinetic capillary chromatography with direct serum injection

The impact of physico-chemical properties of 25 compounds, including antiepileptic, anti-inflammatory and beta-blocking drugs, on their determination by micellar electrokinetic capillary chromatography (MECC) with direct serum injection (DSI) is discussed. Having a pH 9.2 buffer containing 75 mM sodium dodecyl sulfate (SDS), elution is dependent on hydrophobicity, the order of emergence being basically according to increasing octanol/water partition coefficients (logP values). Peak shape is determined by the dissociation behavior (expressed by pKa) and plasma protein binding (PPB). Sharp peaks are produced by compounds having low PPB and, independently of PPB, by drugs with pKa values which are similar to the buffer pH. Broad or double peaks are established by drugs of low pKa values and significant (> about 40%) PPB. In order to evaluate the effective amount of a protein-bound drug measured by MECC-DSI, serum levels of drugs with different PPB, namely ethosuximide (no PPB), phenobarbital (PPB of about 50%) and naproxen (PPB > 99%) have been determined by both MECC-DSI and MECC with extract injection (MECC-EXI). In each case, with more than 40 sera, there is good agreement between the two sets of data. Thus, employing MECC-DSI, total amounts of drugs are determined, i.e. a complete release of the drugs from the proteins is effected by the impact of dodecyl sulfate on the sampled proteins.

Sub- and supercritical fluid chromatography on packed columns: a versatile tool for the enantioselective separation of basic and acidic drugs

Various chiral stationary phases were investigated in sub- and supercritical fluid chromatography for the separation, without derivatization, of basic (beta-blockers, benzodiazepines) and acidic (nonsteroidal anti-inflammatory drugs, beta-agonists) pharmaca. For all racemates, baseline separation was achieved within short analysis times. For several solutes, the high resolution obtained allowed injection of milligram amounts and semipreparative collection of the enantiomers. The parameters affecting enantioselectivity (column efficiency, influence of modifiers and basic or acidic additives, and temperature) have been studied. Enantiomerization of 3-OH-benzodiazepines could be suppressed by working at low temperatures or by using acetonitrile as a comodifier. Serial coupling of different chiral stationary phase columns resulted in a column triplet (Chiralpak AD, an amylose derivative; Chiralcel OD, a cellulose derivative; and Chirex 3022, a Brush-type with pi-donor characteristics) on which all solutes investigated could be baseline separated.

A structure activity relationship study on 1-isopropylamino-3-(2'-substituted naphthoxy)-propan-2-ois analogs

The structure activity relationship of 1-isopropylamino-3-(2'-substituted naphthoxy) propan-2-ois analogs, which are beta-adrenergic blocking drugs, is discussed. The blocking activity of these compounds is found to be dominantly controlled by electronic and steric factors. Significant correlations have been obtained between the blocking activity and negentropy, equalized eletronegativity and partial charge.

Studies on agents with vasodilator and beta-blocking activities. I

A series of hydrazinopyridazine derivatives combined with a beta-blocking side chain were synthesized. When they were given intravenously to anesthetized rats, some of them exhibited both hypotensive and beta-blocking activities. Their structure-activity relationships for hypotensive and beta-blocking activities are discussed. Compound 11c had the best profile and was selected for further study.

The [(methyloxy)imino]methyl moiety as a bioisoster of aryl. A novel class of completely aliphatic beta-adrenergic receptor antagonists

Previous studies in the field of beta-adrenergic drugs had supported the hypothesis of the existence of a bioisosterism between the [(methyleneamino)oxy]methyl moiety (C = NOCH2, MAOMM) of type B beta-blocking drugs and the aryl (Ar) of type A beta-blocking agents. In the MAOMM, however, the carbon of the CH2 linked to the oximic oxygen possesses a hybridization (sp3) and a geometry different from those of the corresponding carbon of Ar which possesses an sp2 hybridization. Furthermore, in the MAOMM, in its preferred conformation, the unsaturated portion (C = N) is situated in a spatial area which does not correspond exactly to the area occupied by Ar. The formal inversion of the atomic sequence C = NOCH2 of the MAOMM leads to a different type of group, the [(methyloxy)imino]methyl moiety (CH2ON = C, MOIMM), which, in the E configuration, appears to present greater steric and electronic analogies with an Ar, with respect to the MAOMM. On the basis of these observations, some completely aliphatic (E)-N-(3-amino-2- hydroxypropylidene)(alkyloxy)amino derivatives of type C (11a,b and 12a, b) were synthesized, the their beta-adrenergic properties were compared with those of the corresponding [(methyleneamino)oxy]-methyl isomers of type B (19a, b and 20a, b). The similar beta-adrenergic properties of 11, 12 and 19, 20 evaluated in vitro both by radioligand binding assays and by functional tests on isolated preparations, are discussed on the basis of considerations regarding the spatial correspondences and electronic analogies between the MOIMM and the MAOMM.

Quantitative relationships between the structure of beta-adrenolytic and antihistamine drugs and their retention on an alpha 1-acid glycoprotein HPLC column

Chromatographic retention parameters of a series of 7 beta-adrenolytics and of 12 antihistamine drugs were determined employing an alpha 1-acid glycoprotein (AGP) high-performance liquid chromatographic (HPLC) column. For the group of antihistamines capillary electrophoretic (CE) retention was additionally measured in the presence of either AGP or human serum albumin (HSA). Two series of solutes hydrophobicity parameters were obtained by reversed-phase HPLC on an immobilized artificial membrane (IAM) column. The solutes studied were subjected to molecular modelling and the structural descriptors obtained were applied in studies of quantitative structure-retention (protein binding) relationships (QSRR). It was found that retention on AGP correlates well with the literature on physiological protein binding data. This retention was demonstrated to depend on hydrophobicity: to a lesser extent in the case of beta-adrenolytics and strongly in the case of antihistamines. Hydrophobicity, along with molecular width and electron excess charge on aliphatic nitrogen was demonstrated to describe retention of antihistamines on AGP. The AGP column is recommended as a convenient reactor for studies of drug-protein interactions. Preliminary CE data do not correlate with the HPLC data.

An enantiomer-enantiomer interaction of (S)- and (R)-propafenone modifies the effect of racemic drug therapy

BACKGROUND

Therapy with racemic compounds produces effects that can be attributed to both (S)- and (R)-enantiomers. Here we have tested the hypothesis that an enantiomer-enantiomer interaction would modulate the effects of treatment with a racemate, the antiarrhythmic propafenone. Previous studies have shown that while the enantiomers of propafenone exert similar sodium channel-blocking (QRS widening) effects, it is the (S)-enantiomer that produces beta-blockade; moreover, we have demonstrated recently that (R)-propafenone inhibits the metabolism of (S)-propafenone in vitro.

METHODS AND RESULTS

This single-blind, randomized study compared the effects of (R/S)-, (S)-, (R)-propafenone (150 mg q 6 hours for 4 days) and placebo on QRS duration (delta QRS) and on maximum exercise heart rate (delta HRmax), an index of beta-blockade. The clearance of (S)-propafenone was significantly lower (-55 +/- 24%, P < .001) during treatment with (R/S)-propafenone than with the (S)-enantiomer alone, and delta HRmax was significantly altered during (R/S)-propafenone (-8.8 +/- 6.6 beats per minute; P < .01) and during (S)-propafenone (-4.3 +/- 4.8 beats per minute; P < .01) but not during (R)-propafenone (-1.8 +/- 6.4 beats per minute) or placebo (0.3 +/- 7.1 beats per minute). In contrast, (R/S)-, (S)-, and (R)-propafenone all prolonged QRS compared with placebo.

CONCLUSIONS

These data indicate that (R)-propafenone impairs the disposition of (S)-propafenone in humans. As a result, the beta-blocking effects of 150 mg of racemic propafenone (75 mg of the [S]-enantiomer) were more pronounced than those of 150 mg of (S)-propafenone alone. Thus, the effects of racemic drug therapy are not necessarily those predicted by summation of the effects of the individual enantiomers.

Structure of the beta-blocker/vasodilator agent prizidilol, DL-6-(2-[3-(tert-butylamino)-2-hydroxypropoxylphenyl)-3-pyridazinylhydr azine hemisulfate monohydrate

Prizidilol, a compound combining vasodilator and beta-blocker functionalities in the same molecule, has been synthesized and characterized by Smith Kline and French Research Ltd. Crystal data: C17H25N5O2 x 1/2H2SO4 x H2O, M(r) = 398.47, orthorhombic, a = 10.722 (2), b = 11.635 (6), c = 34.105 (3) A, V = 4254.61 A3, Pbnm (non-standard form of Pnma) (D16(2h), No. 62), Z = 8, F(000) = 1704, Dx = 1.244 Mg m-3, mu(Cu K alpha) = 11.673 cm-1, R = 0.064 for 2432 independent reflections with I > 3 sigma(I). Prizidilol shows strong conformational similarities to propranolol and is protonated at the secondary amine. The 6-phenyl-3-hydrazinopyridazine residue is not planar. The hydroxy group at the asymmetric carbon is disordered so that both enantiomers are found at each molecular site. The sulfate ions and disordered water molecules lie in the crystallographic mirror plane.

Effects of organic mobile phase modifiers on elution and separation of beta-blockers in micellar electrokinetic capillary chromatography

A study was made of the effect of organic modifiers (acetone, acetonitrile, ethanol, ethylene glycol, methanol and 2-propanol) in phosphate buffer (0.08 M) containing 15 mM cetyltrimethylammonium bromide as surfactant on the elution and separation of eleven common beta-adrenergic blocking agents. The amount of the modifier was varied from 0.1 to 10.0% (v/v). At maximum addition, the organic solvents increased the viscosity of the buffer solution as follows: acetone 16%, acetonitrile 9%, ethanol 26%, ethylene glycol 27%, methanol 20% and 2-propanol 29%. In contrast to the migration time of the other beta-blockers, that of labetalol was not increased by the addition of organic solvent to the buffer solution. Rather, labetalol eluted more quickly with increase in the amount of modifier, and thereby effected changes in the elution order of the beta-blockers. The addition of modifiers also affected the resolution, and the best resolution values were achieved with the following amounts of organic solvent in MEKC buffer: acetone 0.1%, acetonitrile 0.1-0.5%, ethanol 5.0-7.5%, ethylene glycol 1.0-2.5%, methanol 5.0% and 2-propanol 1.0-2.5% (v/v). No significant relationship was found between the elution order and separation and the structure of the beta-blockers in micellar electrokinetic capillary chromatography with an organic modifier in buffer solutions.

[The HPLC analysis of chiral beta-receptor blockers]

Investigations on direct separation by RP-HPLC of selected enantiomeric beta-adrenergic active agents are described. R- and S-1-phenylethylisocyanate (PEIC) as well as (1S)-(+)-campher-10-sulfonylchloride (CSC) are used for the derivatization of the compounds. Correlations between chromatographic data and various influences (pH, temperature, reaction time, concentration of reagens a.o.) have been discussed. The behaviour of derivatized and underivatized analytes on RP-columns is described in dependence on buffer concentration of the mobile phase. The investigated beta-adrenergic agents were partly separated after derivatization with PEIC, whereas this was not possible with CSC as derivatization reagent.

Enantioselective bioanalysis of beta-blocking agents: focus on atenolol, betaxolol, carvedilol, metoprolol, pindolol, propranolol and sotalol

The recent developments in enantioselective HPLC-separation techniques are impressive and are driven by industrial and academic interests; thus there is for instance a high demand for developing stereoselective assays for chiral drugs in biological fluids. The beta-blocking agents, which possess an amino-propanol- or -ethanol side chain with at least one chiral centre, represent one of the most intensively investigated groups of more than 40 drugs introduced world wide. Seven of the most popular beta-blockers were chosen as representatives: atenolol; betaxolol; carvedilol; metoprolol; pindolol; propranolol; and sotalol, these span the whole range of lipophilicity to hydrophilicity (polarity). Enantioselective HPLC bioassays for these beta-blockers published so far, including techniques based on chiral derivatizing agents (CDAs), chiral stationary phases (CSPs) and chiral mobile phase additives (CMPAs) have been reviewed and documented in the light of general aspects together with pharmacokinetic and pharmacodynamic considerations.

Effect of beta-adrenergic receptor antagonists on nicotine-induced tail-tremor in rats

The effects of various beta-adrenergic receptor antagonists on nicotine-induced tail-tremor were investigated in rats. Atenolol (5 and 10 mg/kg, IP), arotinolol (5 and 10 mg/kg, IP), and carteolol (5 and 10 mg/kg, IP), hydrophilic beta-adrenergic receptor antagonists, did not affect the tail-tremor induced by nicotine given at a dose of 0.5 mg/kg SC. However, propranolol (5-20 mg/kg, IP) and pindolol (5-20 mg/kg, IP), nonselective and lipophilic beta-adrenergic receptor antagonists, did suppress the tail-tremor dose dependently. In contrast, metoprolol (5-20 mg/kg, IP), lipophilic and beta 1-selective adrenergic receptor antagonists, did not show such an effect. These results suggest that nicotine-induced tail-tremors may be mediated through central beta 2-adrenergic receptors as an appearance and developmental mechanism.