Comparison of a noncardioselective beta-adrenoceptor blocker and a cardioselective blocker in reducing aqueous flow in humans

In a double-masked crossover study, the dose-response relationship for aqueous flow was determined for four concentrations of betaxolol hydrochloride and levobunolol hydrochloride in 19 normal subjects. One eye of each subject received every concentration of both drugs. Each concentration was administered once daily for 1 week. The fellow eye received a placebo. Aqueous flow was measured for several hours on the last day of administration of each concentration beginning immediately after drug administration. For levobunolol, the mean decrease in aqueous flow compared with baseline was 8% after 1 week's treatment with 0.017% levobunolol, 15% after treatment with 0.05%, 20% after treatment with 0.167%, and 32% after treatment with 0.5%. For betaxolol, the mean decrease in aqueous flow compared with baseline was 3% after 1 week's treatment with 0.017% betaxolol, 12% after treatment with 0.05%, 18% after treatment with 0.167%, and 17% after treatment with 0.5%. Levobunolol-treated eyes but not betaxolol-treated eyes showed a significant drug effect 1 week after discontinuing the drug therapy. The relative potency of the noncardioselective drug was greater than that of the beta 1-cardioselective drug, but the difference in potency was much less than would be expected solely based on their relative affinity for beta 2-receptors in other species and tissues.

The effect of timolol, betaxolol and levobunolol on the surface of rabbit cornea

Pigmented rabbits were treated with timolol maleate, betaxolol hydrochloride or levobunolol hydrochloride eye drops twice a day for six months. Animals of the same age group and breed were used as controls. There were no differences observed in corneal epithelium with light and transmission electron microscopy. With scanning electron microscopy, in the timolol and betaxolol treated animals the picture of the corneal surface was similar to that of normal rabbit corneas after exposure to air. In scanning electron micrographs of the levobunolol treated animals, the corneal surface resembled the corneas of normal rabbits treated with artificial tears.

Pharmacodynamic comparison of L-bunolol with propranolol, metoprolol, and placebo

Twelve healthy volunteers received single oral doses of propranolol (80 mg), metoprolol (100 mg), L-bunolol (2 mg), and placebo in a four-way crossover study. Blood pressure, ventricular rate, and echocardiographically determined ejection fraction, ejection time, and mean rate of circumferential fiber shortening (mVcf) were measured before dosing and at multiple time points during 10 hours after each dose, with subjects maintained in the supine position. Reductions in systolic and diastolic blood pressure following administration of each of the beta blockers were greater than those observed with placebo, but differences among the four treatments were not significant. Heart rate reductions with the beta blockers differed significantly from placebo (P less than .001), but differences among the three beta blockers were not significant. Differences among the four treatments in mVcf decrement did not attain significance at the 5% level (.05 less than P less than .1), and there were no significant differences in ejection-time prolongation or ejection-fraction reduction. Thus, reduced blood pressure, heart rate slowing, and reduced cardiac contractility may be associated with placebo treatment and may indicate the need for placebo controls in studies of the cardiovascular effects of beta blockers. Despite differing secondary pharmacologic properties, the three beta blockers reduced heart rate to a similar extent. Other effects of the beta blockers on blood pressure and cardiac contractility could not be consistently distinguished from those associated with placebo.

Ocular and cardiac beta-antagonism by timolol prodrugs, timolol and levobunolol

Topically applied O-butyryl timolol, O-pivaloyl timolol and levobunolol (0.25 micrograms) antagonized isoproterenol-induced ocular hypotension for 8 hrs whereas timolol (0.25 micrograms) was shorter acting (4 hrs). Timolol (25 micrograms) produced greater antagonism of isoproterenol-induced tachycardia than did O-butyryl and O-pivaloyl timolol (25 micrograms). These results suggest that, at similar doses, O-butyryl and O-pivaloyl timolol produce high concentrations of timolol in ocular tissues and undergo redistribution more slowly into the systemic circulation than does topical timolol. Under certain circumstances, prodrugs may provide a mechanism for increasing selectivity and extending the duration of action in the target organ as well as decreasing systemic effects.

Ocular levobunolol. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Levobunolol is a potent non-selective beta-adrenoceptor blocking agent used for the topical treatment of increased intraocular pressure in patients with chronic open angle glaucoma or ocular hypertension. In comparative studies of up to 2 years' duration levobunolol 0.5 to 1% reduced intraocular pressures by about 30% and adequately controlled intraocular hypertension in 50 to 85% of those treated. These results were significantly superior to those produced by placebo and comparable to the responses achieved with ocular timolol in double-blind controlled trials. Levobunolol has been well tolerated, producing only minor changes in objective and subjective ophthalmic and systemic parameters. Adverse reactions resulted in approximately 5% of patients withdrawing from treatment with levobunolol which was equivalent to that observed with timolol. Thus, ocular levobunolol is a well-tolerated and effective therapy for the management of raised intraocular pressure, and is a suitable alternative to ocular timolol in patients with chronic open angle glaucoma or ocular hypertension.

Dihydrolevobunolol is a potent ocular beta-adrenoceptor antagonist

The ocular beta-adrenoceptor antagonist activity of dihydrolevobunolol (DHLB), the major ocular and systemic metabolite of levobunolol was investigated by determining its ability to block isoproterenol-induced ocular hypotension in normotensive rabbits. Topically-applied 0.001% and 0.01% DHLB virtually abolished the response to isoproterenol, indicating a beta-blocking potency similar to that of timolol. Thus, the ocular metabolism of levobunolol leads to the formation of a highly potent beta-adrenoceptor antagonist that may contribute to its clinical efficacy.

The effect of levobunolol on aqueous humor dynamics

We evaluated the acute effects of installation of 0.5% levobunolol on aqueous humor dynamics in a double-masked study in 18 patients with ocular hypertension. Aqueous flow was measured by fluorophotometry and total outflow facility by tonography. Aqueous flow decreased approximately 29% in the eyes treated with levobunolol. Total outflow facility and episcleral venous pressure measurements were similar in levobunolol-treated eyes and contralateral eyes treated with vehicle. A 36% decrease in intraocular pressure was observed in the levobunolol-treated eyes and a slight intraocular pressure reduction was seen in the vehicle-treated eyes. The results of this study indicate that, similar to timolol, levobunolol lowers intraocular pressure primarily by decreasing aqueous humour production.

[Effect of commercial beta blockers and their combination with artificial tears on the duration of tear film stability]

The influences of 8 different beta-blockers on the tear film stability-measured on the breakup time (BUT) of normal and healthy volunteers-was compared. All beta-blockers led to BUT reduction, however, the lowest influence was observed with levobunolol. The duration of this effect was compared with that of levobunolol, timolol and metipranolol. While the minor BUT alterations induced by levobunolol recovered after 30 min and were completely restored after 1 h, those of the two other beta-blockers lasted for over 2 h. The combination of timolol 0.5% with different artificial tears containing mainly polyvinyl alcohol (PVA) 1.4%, methylcellulose and polyacrylic acid initially led also to BUT reduction. The best results were obtained with PVA 1.4%.

[Immediate effect of a topical beta-blocker on breakup time]

The comparison of different beta-blocking agents and their influences on the breakup time (BUT) reveals that levobunolol reduces the BUT in the same way as physiologic saline solutions, while other beta-blockers lead to an enormous reduction of BUT.

Influence of beta-adrenoceptor antagonists on spontaneous rate and on force of contraction of isolated rabbit atria

The influence of beta-adrenoceptor antagonists on the spontaneous rate and on force of contraction of the myocardium was studied independently on spontaneously beating right and electrically driven isolated left atria of rabbit. On spontaneous rate, practolol had sympathomimetic effect only, N-isopropylmethoxamine (IMA), had both sympathomimetic as well as depressant effects, whereas alprenolol, procinolol, bunolol and H 35/25 had depressant effects only in higher concentrations. The order of potency was procinolol greater than bunolol greater than alprenolol greater than H 35/25 greater than and IMA. On the contractions of isolated left atria, all beta-adrenoceptor antagonists produced concentration-dependent depressant effect. In relation to procinolol, these agents were 5-125 times less potent for depressing the contractions of left atria by 15% and the order of beta-potency was procinolol greater than alprenolol greater than bunolol = H 35/25 greater than IMA greater than and practolol. The present results indicate that the depressant effects of beta-adrenoceptor antagonists on spontaneous rate of right atria and on contraction of isolated left atria are not related to each other.

l-Bunolol and propranolol: oral and intravenous beta-adrenoceptor blocking activity in rats compared to dogs and humans

To determine the pharmacological significance of reported differences between species in l-bunolol metabolism, oral and intravenous beta-adrenoceptor blocking activity against an isoproterenol-induced tachycardia was compared in dogs, rats, and humans. Propranolol was similarly studied in rats and dogs. Species differences in intravenous potency were minimal for both compounds in contrast to oral dose studies. Oral to intravenous ratios of doses causing a comparable degree of beta-adrenoceptor blockade after l-bunolol were: rat, 212; dog 4; and human, 5. For propranolol, the oral to intravenous dose ratios were 210 and 32 for the rat and dog, respectively. These pharmacological findings show major differences in the rat compared to dogs and humans and may be explained in part by differences in the urinary excretion patterns of l-bunolol in the various species.

Metabolism of l-bunolol

The metabolism of l-bunolol, a new beta-blocking drug, was studied in man after single oral 3-mg doses of 3H-labeled compound. Absorption from the gut was rapid and virtually complete. Peak levels of bunolol and of dihydrobunolol, an active metabolite, were observed at 1 hr. Excretion of the administered radioactivity was mainly into the urine (78% in 4 days), with only 3% appearing in the feces. Bunolol, bunolol glucuronide, bunolol sulfate, dihydrobunolol, and dihydrobunolol glucuronide were identified and quantified in the plasma. These compounds represented 82% of the radioactivity in plasma at 30 min and 55% at 24 hr. Plasma half-lives (+/-S.D.) were estimated to be 6.1 +/- 0.3 hr for bunolol, 9.1 +/- 1.9 hr for bunolol glucuronide, 17.4 +/- 2.5 hr for bunolol sulfate, 7.1 +/- 0.5 hr for dihydrobunolol, and 7.7 +/- 0.8 hr for dihydrobunolol glucuronide.

[Effects of pretreatment with carteolol on metabolic changes induced by coronary artery ligation in dog left ventricular wall (author's transl)]

Effects of coronary artery ligation on myocardial glycogenolysis were studied in the endo- and epicardial layers of the left ventricular wall in dogs pretreated with 10 or 100 microgram/kg (i.v.) of carteolol, a potent beta-adrenergic blocking agent. Coronary artery ligation was performed by ligating one of the small branches of the left anterior descending coronary artery. In control (saline-pretreated) dogs, an increase in phosphorylase alpha activity and an increase in breakdown of glycogen were observed in both endo- and epicardial layers after coronary artery ligation. In the presence of 10 or 100 microgram/kg of carteolol, however, increases in phosphorylase alpha activity and increase in breakdown of glycogen were not observed in either the endo or epicardial layers. These results indicate that pretreatment of the dog with carteolol inhibits the increase in glycogenolysis caused by coronary artery ligation. Nevertheless, carteolol did not completely inhibit the coronary artery ligation-induced increase in glucose-6-phosphate and lactate levels, and the coronary artery ligation-induced decrease in phosphocreatine level, particularly in the endocardial layers.

Effect of a new beta-adrenergic blocker, l-bunolol, on blood pressure and on the renin-aldosterone system

The antihypertensive effect of a new beta-adrenergic receptor blocker, l-bunolol, was evaluated in 11 hospitalized hypertensive patients of whom four belonged to the high-renin, five to the normal-renin, and two to the low-renin subgroup. There was a significant decrease in blood pressure in most patients, often to normal. Moreover, plasma renin levels were nearly always markedly suppressed, and this suppression preceded the fall in blood pressure. While most high and normal renin patients responded, the numbers of patients within each subgroup were too small to correlate the blood pressure responses with changes in renin levels. There was a significant induced decrease in aldosterone excretion, which usually paralleled the renin suppression. Pulse rate was also consistently reduced during treatment. No weight gain was observed, except in one patient who developed overt congestive cardiac failure. No other side effects were recorded. Ii is concluded that l-bunolol is another beta-blocking drug with significant antihypertensive action. It was found to be effective in cases that were resistant to propranolo. It is well tolerated and safe to use, provided that early evidence of fluid retention is sought for and treated immediately.

A comparative study of the effects of OPC-1085 and propranolol on isolated guinea pig atrium

Effects of a newly synthesized beta-blocker, 5-(3-tert-butylamino-2-hydroxy) propoxy-3,4-dihydrocarbostyril (OPC-1085) were compared with those of propranolol. OPC-1085 had a potency about 3 times greater than that of propranolol in blocking the positive inotropic and chronotropic effects of isoprenaline on the isolated guinea pig atrium. At a concentration of over 3 X 10(-5) M OPC-1085 produced negative inotropic and chronotropic effects. However, these effects were about 10 times weaker than those of propranolol. Suppressing effects on the rate of rise and on the maximum driving frequency of action potentials were also more than 10 times less than those of propranolol. There was almost no change in the action potential of vagus nerve after a 10 min treatment with OPC-1085 (10(-5) M), while the action potential was reduced to 60-70% with propranolol (10(-5) M).

[A comparison of the effects of the beta-adrenergic blockers, carteolol (OPC-1085), propranolol and alprenolol on isolated rat cardiac muscles (author's transl)]

The effects of carteolol, propranolol and alprenolol were studied by using spontaneously contracting atria, atrial muscle and papillary muscle prepared from rat hearts. Propranolol, alprenolol and carteolol caused decreases in atrial rate and in contractile tension of electrically driven cardiac muscles in concentrations of 10(-6) to 10(-5) g/ml, 10(-6) to 10(-5) g/ml and 10(-4) g/ml, respectively. These compounds, also, effectively prevented electrically-induced atrial arrhythmias in these concentrations. Contractile tension of the cardiac muscles was increased by carteolol in concentrations of 10(-7) to 10(-6) g/ml. The refractory period of the cardiac muscles was prolonged in the presence of alprenolol (10(-7) to 10(-6) g/ml) or carteolol (10(-6) to 10(-5) g/ml). The refractory period of the papillary muscle was increased by 10(-7) to 10(-6) g/ml of propranolol. The maximum driven frequency (MDF) of the atrial muscle was reduced by 5X10(-8) to 10(-7) g/ml of carteolol or by 5X10(-8) g/ml of alprenolol, and MDF of the papillary muscle by 5X10(-7) g/ml of propranolol. In extremely high concentrations, these compounds significantly reduced MDF of the cardiac muscle. These results suggest that the antiarrhythmic action of alprenolol and carteolol is more predominant in atria than in ventricles, whereas the reverse is true for propranolol.

Levo-bunolol and propranolol: further evaluation of oral beta-blocking activity in conscious dogs

The oral beta-adrenoceptor blocking activity of bunolol, propanolol, and their levo-isomers was compared against isoproterenol- and treadmill exercise-induced tachycardias in normal conscious dogs. Relative potencies against isoproterenol were (ascending order): propranolol=1, levo-propranolol=2, bunolol=40, and levo-bunolol=102. Large oral doses of levo-bunolol and propranolol suppressed exercise tachycardia by only 18% (range 10 to 22%). Compared to the isoproterenol response, the tachycardia associated with severe exercise in the healthy trained dog was largely resistant to beta-receptor blockade showing factors other than beta-receptor stimulation to be involved. Differences in duration of beta-blockade were observed at equiactive doses of levo-bunolol and propranolol. The isoproterenol response had returned to greater than 50% of control by 12 hr after propranolol but was less than 10% of control at 12 hr after levo-bunolol. The time to 50% recovery of the exercise tachycardia was 24 hr after levo-bunolol and 6 to 9 hr after propranolol. The results show oral levo-bunolol to be considerably more potent and to have a longer duration of action than propranolol in inhibiting both isoproterenol and exercise-induced tachycardias in conscious dogs.