Gel formulations containing catanionic vesicles composed of alprenolol and SDS: effects of drug release and skin penetration on aggregate structure.

To fully utilize the extended contact time of gel formulations a novel formulation with drug containing catanionic aggregates offering prolonged drug release and skin penetration were investigated. This study aimed to further explore the drug release process from catanionic vesicles in gels. Catanionic vesicles were formed from alprenolol and sodium dodecyl sulphate. Physical gels composed of catanionic vesicles and a SoftCAT polymer were used as well as covalent Carbopol gels. Drug release was measured in vitro using a modified USP paddle method and the skin penetration was studied using dermatomized pig ear skin mounted in horizontal Ussing chambers. The aggregate structure was visualized with cryo-TEM during the drug release and skin penetration process. The study results show that catanionic vesicles are present in the formulations throughout the drug release process and during the clinically relevant skin application time. Hence, the decreased skin penetration rate stems from the prolonged release of drug substance from the gels. The rheological investigation shows that the gel structure of the physically cross-linked gels is maintained even as the drug substance is released and the gel volume is decreased. These findings indicate that the applicability of formulations like these is a future possibility.

An investigation into the influence of drug lipophilicity on the in vivo absorption profiles from subcutaneous microspheres and in situ forming depots.

Drug lipophilicity is known to have a major influence on in vivo drug absorption from intramuscularly and subcutaneously administered solutions. Indeed, chemical modification to increase drug lipophilicity is used to enable sustained drug release from solutions. In contrast to the wealth of knowledge on drug release from simple solutions, the influence of drug lipophilicity on its release from controlled release formulations, such as, microparticles and in situ forming depots, have not been systematically studied. Controlled release vehicles are designed to 'control' drug release, hence, in vitro studies show negligible influence of drug lipophilicity on release. The situation could however be different in vivo, due to interactions between the vehicle and biological tissue. We therefore investigated the influence of drug lipophilicity on its in vivo release in rats from two controlled release formulations, PLGA microparticles and in situ forming depots. Both systems exhibited a burst drug release. Subsequent to the burst release, we found that lipophilicity did not influence the rate or extent of drug absorption from the two formulations over a 10-day study period, which would imply that drug partitioning out of the depots was not the main mechanism of drug release from both formulations. This study must however be repeated with a greater number of animals to increase its power.

Atrial natriuretic peptide enhances cortisol secretion from guinea-pig adrenal gland: evidence for an indirect paracrine mechanism probably involving the local release of medullary catecholamines.

Atrial natriuretic peptide (ANP) is a regulatory hormone widely expressed, along with its receptors, in organs and body tissues. ANP is well known to inhibit aldosterone secretion from mammalian adrenals, but its effect on glucocorticoid-hormone production is controversial. In vivo experiments showed that prolonged ANP administration raised the plasma concentration of cortisol in both normal and dexamethasone/captopril-treated guinea pigs (i.e. in animals with pharmacologically interrupted hypothalamic-pituitary-adrenal axis and renin-angiotensin system). ANP did not affect cortisol secretion from dispersed guinea pig zona fasciculata-reticularis cells, but enhanced catecholamine release from adrenomedullary cells. ANP stimulated cortisol output from guinea pig adrenal slices containing medullary chromaffin tissue, and the beta-adrenoceptor antagonist l-alprenolol blocked this effect. The conclusion is drawn that ANP, when the structural integrity of the adrenal gland is preserved, is able to enhance glucocorticoid secretion in guinea pigs, through an indirect mechanism involving the rise in the catecholamine release, which in turn, acting in a paracrine manner, stimulate secretion of inner adrenocortical cells.

Chronic infusion of beta-adrenoceptor antagonist and inverse agonists decreases elevated protein kinase A activity in transgenic mice with cardiac-specific overexpression of human beta 2-adrenoceptor.

Neutral antagonists and inverse agonists can produce different cellular responses in some systems. The effects of chronic (14-day) infusion of three ligands, ICI-118,551, carvedilol, and alprenolol were examined in cardiac tissue from wild-type and transgenic mice with cardiac-specific overexpression of the human beta2-adrenoceptor. These ligands vary in their negative efficacy at the human beta2-adrenoceptor, with two (ICI-118,551 and carvedilol) behaving as inverse agonists and one (alprenolol) behaving as a neutral antagonist. Cardiac tissue from the transgenic mice exhibited elevated levels of protein kinase A activity and G protein receptor kinase-2. Fourteen-day infusions of the three ligands lowered the elevated levels of protein kinase A activity of the transgenic hearts to control levels. Alprenolol and carvedilol also decreased G protein receptor kinase-2 amounts to control levels. The left atria from transgenic mice exhibited an impaired inotropic response to histamine relative to responses of wild-type mice atria. Infusions of the inverse agonists and a neutral antagonist at the beta2-adrenoceptor significantly restored the impaired histamine response. Restoration of protein kinase A activity and the impaired histamine responses in the atria from transgenic mice can be observed following 14-day infusions of both a neutral antagonist and inverse agonists. The reversal of the effects of the transgene by both inverse agonists and a neutral antagonist suggests that agonist occupancy, and not spontaneous activity, of the beta2-adrenoceptor is producing the elevated protein kinase A activity and the impaired histamine response.

Relationship between amount of beta-blockers permeating through the stratum corneum and skin irritation after application of beta-blocker adhesive patches to guinea pig skin.

We evaluated the relationship between the cumulative amounts of 5 kinds of beta-blockers (alprenolol, oxprenolol, timolol, acebutolol and atenolol) permeating through the stratum corneum and a* values obtained by measuring the formation of erythema, a skin irritation reaction, with a chromameter after transdermal application of adhesive patches containing 2 beta-blocker to the skin of guinea pigs. The cumulative amount of beta-blocker released from each adhesive patch to the skin increased with the increase in application time. The contents of alprenolol, oxprenolol and timolol in the stratum corneum and in the stripped skin increased markedly up to 4 h after application and thereafter were maintained at high levels up to 24 h. The contents of acebutolol and atenolol, on the other hand, increased up to 24 h, but these values were low. a* values of all adhesive patches 24 h after application were higher than those before application. The correlation coefficients between the cumulative amounts of alprenolol, oxprenolol, timolol, acebutolol or atenolol permeating through the stratum corneum and (delta a* -delta a*Placebo) values were 0.739, 0.717, 0.722, 0.551 and 0.633, respectively. The correlation coefficient calculated by averaging the cumulative amounts of 6 kinds of beta-blockers permeating through the stratum corneum [including propranolol which was reported previously (Kobayashi I., et al., Biol. Pharm. Bull., 19, 839-844 (1996))] was 0.731, higher than the correlation coefficient between contents of these beta-blockers in the stripped skin and (delta a* -delta a*Placebo) values (r = 0.552). This suggests that there was a high correlation between the cumulative amounts of beta-blockers permeating through the stratum corneum and (delta a* -delta a*Placebo) values.

Ocular delivery of the beta-adrenergic antagonist alprenolol by sequential bioactivation of its methoxime analogue.

Ocular delivery of alprenolol, a beta-adrenergic antagonist, by site-specific bioactivation of its methoxime analogue results in significant and prolonged decrease of the intraocular pressure in rabbits after topical administration. Alprenolone methoxime is stable in isotonic phosphate vehicle but undergoes enzymatic hydrolysis to the corresponding ketone in the eye. The ketone is then converted to alprenolol by a carbonyl reductase present in the iris-ciliary body. The benefit of this chemical delivery system approach includes the facile release of a potential antiglaucoma agent only at the site of the action; thus, unwanted systemic effects of the drug can be avoided.

Improved delivery through biological membranes. LVI. Pharmacological evaluation of alprenoxime--a new potential antiglaucoma agent.

A new site-specific chemical delivery system (CDS) for alprenolol was designed and investigated as a potential novel antiglaucoma agent. The effect of this compound, alprenoxime (AO), on the intraocular pressure (IOP) of rabbits was evaluated after its uni- and bilateral administration. AO produced significant reduction of the IOP starting at 30 min and lasting for more than 6 hr after its topical administration. Both in rats and in rabbits the i.v. bolus injection of AO (6 mg/kg) led to insignificant transient bradycardia, while no activity was found after oral or topical administration. Alprenolol (ALP) in a similar dose produced a sustained and significant bradycardia for more than 30 min. When the beta-adrenergic blocking activity was assessed against isoprenaline-tachycardia, the same results were obtained, i.e., AO led to a transient brief activity, whereas ALP produced a significant long-lasting beta blockade. These results support the potent ocular hypotensive action and the weak systemic beta-adrenergic blocking and cardiovascular activity of AO: a significant improvement in the therapeutic index. This finding recommends alprenoxime as a potent site-specific antiglaucoma agent with minimal systemic side effects.

Continuous alprenolol infusion for control of hypertension in the acute stage of ruptured intracranial aneurysms.

The clinical benefits and hemodynamic effects of continuous alprenolol infusion for control of hypertension in the acute stage of ruptured cerebral aneurysms were investigated. Twenty-five patients manifesting systemic hypertension (greater than 160/100 mmHg) were treated with alprenolol, a beta-adrenergic antagonist, phentolamine, an alpha-adrenergic antagonist, and trimethaphan camsilate, a ganglionic blocker, given intravenously. All drugs decreased the mean arterial blood pressure significantly. However, alprenolol decreased the heart rate and cardiac index while phentolamine increased them. Alprenolol also decreased arterial catecholamine and renin activity, but caused no change in central venous pressure, pulmonary capillary wedge pressure, pulmonary vascular resistance, and systemic vascular resistance. The results indicate the usefulness of continuous alprenolol infusion for the control of acute hypertension in hemorrhagic cerebrovascular disease. The mode of action of alprenolol is also discussed.

Endoscopic evaluations of potentially ulcerogenic drugs. A new in vivo porcine test model.

A new test model in living pigs is presented. The model is easy to manage and, in contrast with other test models, it is unnecessary to euthanize the animals. The animals keep their value and can be slaughtered later. We advise the use of only one period of 'pill-feeding', because more periods will stress the animals and probably inhibit normal weight gain. We suggest this model as the method of choice in the evaluation of local ulcerogenic effects of drug substances in oral pharmaceutical formulations. An endoscopic evaluation in vivo of the ulcerogenic effect of potassium chloride in different microencapsulated preparations, wax-matrix formulations, a liquid preparation, and a noncoated reference formulation showed one of the microencapsulated preparations to induce a significantly lesser degree of gastric mucosal damage than did all the other preparations. The gastric injury following a slow-release iron preparation and alprenolol (Aptine) was similar to that following the slow-release and the wax-matrix preparations of potassium chloride. Potassium chloride mixture caused gastric mucosal damage to the same extent as the other commonly used preparations of potassium chloride. Potassium chloride supplement causes gastric mucosal damage, but the results from the present in vivo porcine test model suggest that the severity of the injury seems to be a matter of appropriate drug formulation.

Oesophageal ulcerations and plasma levels of different alprenolol salts: potential implications for the clinic.

The ulcerogenic effect of five different salts of alprenolol were tested against placebo in a porcine oesophageal test model. The salts with high water solubility, such as the hydrochloride and the fumarate, gave rise to the highest plasma concentrations of alprenolol and evoked serious oesophageal lesions, while the salts with low solubility-the benzoate, maleate and sebacate-had no irritative effect on the oesophagus. The plasma levels of alprenolol were much higher following administration of alprenolol hydrochloride in the oesophagus than after an identical intraduodenal dose of the same salt possibly because of the avoidance of the first-pass degradation during oesophageal absorption.

Determination of (R)-AND (S)-alprenolol-and (R)- and (S)-metoprolol as their diastereomeric derivatives in human plasma by reversed-phase liquid chromatography.

A high-performance liquid chromatographic method is described for the determination of (R)- and (S)-alprenolol and (R)- and (S)-metoprolol in human plasma. Separation of the enantiomers was accomplished after preparation of diastereomeric derivatives with symmetrical anhydrides of tert.-butoxycarbonyl-L-leucine followed by treatment with trifluoroacetic acid at 0 degree C to remove the tert.-butoxycarbonyl group. The separations of the diastereomeric derivatives were performed using a reversed-phase system with muBondapak C18 as support and phosphate buffer pH 3.0 with the addition of acetonitrile as the mobile phase. High stability of the chromatographic system was achieved. The reproducibilities in the determination of (R)- and (S)-alprenolol and (R)- and (S)-metoprolol in human plasma were 9.4 and 9.8% (relative standard deviation) for alprenolol and metoprolol, respectively, at drug levels of 0.5 ng/ml. In two subjects who received single oral doses of alprenolol (100-mg tablet) and metoprolol (50-mg tablet) the plasma levels of the (R)-isomers were lower than for the (S)-isomers.

[Effect of the beta-adrenoblocker alpheprol and the alpha-adrenolytic tropaphen on tolerance to strophanthin in experimental myocardial infarct]. / Vliianie beta-adrenoblokatora alfeprola i alpha-adrenolitika tropafena na tolerantnost' k strofantinu pri éksperimental'nom infarkte miokarda.

The tolerance to strophanthin was studied in acute and subacute experiments on 76 cats at varying time after occlusion of the coronary artery branch. The beta-adrenoblocker alpheprol completely smoothed away the hypersensitivity to strophanthin after the coronary blood flow cessation while the alpha-adrenolytic tropaphen virtually did not affect the tolerance to strophanthin in intact animals even after experimental myocardial infarction.

Alprenolol-induced thrombocytopenia.

A case of alprenolol-induced thrombocytopenia in a 65-year-old woman is reported. She was admitted to the hospital twice with platelet counts below 10X10(9)/l. The platelet count rapidly returned to normal after discontinuation of alprenolol. The reason for the thrombocytopenia was increased platelet destruction.

Effect of alprenolol on mortality among patients with definite or suspected acute myocardial infarction. Preliminary results.

A double-blind study of alprenolol versus placebo was done in patients with definite or suspected myocardial infarction to show the effect of the drug on mortality-rate after a year of treatment in patients aged less than or equal to 65 and to study the tolerance of the drug by patients greater than 65 years of age. The dose given was 5--10 mg intravenously, followed by 200 mg twice a day, orally. Patients in whom beta-blockade was contraindicated were excluded. All deaths, side-effects, and dropouts were recorded. Of the 480 patients in the study, 238 patients received alprenolol and 242 placebo. During the year of follow-up 108 patients dropped out from the study. Mortality was not reduced in patients greater than 65 years of age. In those less than or equal to 65 years alprenolol significantly reduced mortality-rate (20% mortality in placebo group vs 9% in treated group). There was also a significant reduction in mortality-rate among those with definite infarction (28% in the placebo vs 15% in the treated group).

Kinetic studies of dose-dependent metabolism of alprenolol: in vitro and in vivo studies in different species.

Kinetic studies of the metabolism of alprenolol were performed with isolated microsomes from the rat, guinea-pig, dog and man at an initial substrate concentration of 0.17--150 micrometer. In all species the rate of aromatic hydroxylation reached a plateu above 50 micrometer of alprenolol in contrast to the rate of desisopropylation, where consistent saturation level was not obtained. The Km-values for the aromatic hydroxylation in the guinea-pig and man, 2,7 micrometer and 1.3 micrometer respectively, showed no concentration dependency in contrast to the rat (Km1 = 0.20 micrometer, Km2 = 26 micrometer) and the dog (Km1 = 0.78 micrometer, Km2 = 66 micrometer). The apparent Km-value of 0.20 micrometer for aromatic hydroxylation in the rat seemed to be of the same order of magnitude as reported spectral dissociation constant (Ks = 0.34 micrometer). In vivo experiments in the rat by oral administration of 7--700 mu mol/kg demonstrated a dose-dependent presystemic elimination of alprenolol. The urinary excretion of hydroxy-alprenolol was significantly lower after the highest dose. It is proposed, that the saturation of the aromatic hydroxylation, catalyzed by a high affinity site or subspecies of cytochrome P-450 with a low capacity, contributes to the dose-dependent kinetics in vivo.