Effect of indoramin, labetalol and alinidine on sympathetic function in normal man

Labetalol. A reappraisal of its pharmacology, pharmacokinetics and therapeutic use in hypertension and ischaemic heart disease

Since labetalol was first reviewed in the Journal (1978), its scope of therapeutic use has expanded and become better defined. Labetalol is an adrenoceptor blocking drug with combined alpha- and beta-blocking properties. These result in a more favourable haemodynamic profile for labetalol compared with 'pure' beta-blockers or pure alpha-blockers, but also contribute to a wider range, but not an overall increased incidence, of adverse effects. The drug is effective and well-tolerated in patients with all grades of hypertension, but is of particular value in special subgroups such as Black patients, the elderly and patients with renal hypertension. While comparative studies are not extensive, available data show that the drug reduces blood pressure to a similar extent, and in a similar proportion of patients, as 'pure' beta-blockers such as propranolol, pure alpha-blockers such as prazosin, calcium antagonists (nifedipine, verapamil), and centrally acting drugs (clonidine and methyldopa). Labetalol is very effective in hypertensive pregnant women and in hypertensive crises, where it provides good control of blood pressure without serious adverse effects, and where few therapeutic options exist. Few controlled studies have investigated the use of labetalol in deliberate induction of hypotension or prevention of hypertension during anaesthesia, and also in patients with ischaemic heart disease. However, available evidence suggests a role for labetalol in these indications and further studies should aid in clarification of its efficacy in these areas. Thus, with its broad scope of therapeutic use in hypertension labetalol remains an important therapeutic option, and the drug may well find an additional place in the treatment of myocardial ischaemia if further evidence confirms encouraging preliminary findings.

Control of catecholamine-induced tachycardia with alinidine in the anesthetized dog

Sinus tachycardia is a common complication of beta-adrenergic agonist therapy. A new selective bradycardic agent, N-allyl-clonidine, or alinidine, has been found effective against sinus tachycardia caused by a variety of stimuli. To determine whether it would also control catecholamine-induced sinus tachycardia, the effects of alinidine in two groups of anesthetized dogs treated with either dobutamine, 10 microg/ kg/min, or isoproterenol, 0.1 microg/kg/min, were studied. In both groups, alinidine significantly reduced the heart rate (P < .0001 in the dobutamine group, and P < .005 in the isoproterenol-infused dogs). The other hemodynamic effects of dobutamine were not adversely affected by alinidine, while the isoproterenol-infused dogs had a further afterload reduction when treated with alinidine. It is concluded that alinidine is effective against catecholamine-induced sinus tachycardia, possibly through mechanisms not related to beta-adrenergic receptors.

Long-term indoramin therapy in congestive heart failure: a double-blind, randomized, parallel placebo-controlled trial

Twenty-one patients with moderately severe congestive heart failure participated in a double-blind, randomized, parallel placebo-controlled trial designed to evaluate the effects of long-term (2 months) indoramin therapy on rest and exercise hemodynamics, exercise capacity and clinical status of patients with this clinical syndrome. The long-term administration of indoramin in patients (mean dose 50 mg every 12 hours) caused a mild reduction from baseline values in supine rest mean systemic blood pressure and, after dosing, elicited a significant reduction in systemic and pulmonary vascular resistances, pulmonary capillary wedge pressure and heart rate as well as a mild increase in stroke volume. Long-term indoramin therapy caused a small decrease, as compared with baseline exercise responses, in systemic and pulmonary vascular resistance and pulmonary capillary wedge pressure at submaximal levels of exercise. It did not alter hemodynamic variables at maximal exercise, exercise capacity or overall clinical status, compared with findings at baseline or with placebo.

Indoramin. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in hypertension and related vascular, cardiovascular and airway diseases

Indoramin is a postsynaptic selective alpha 1-adrenoceptor antagonist used in the treatment of hypertension. In contrast to some other alpha-blockers, animal studies suggest that its blood pressure lowering effect results from relaxation of peripheral arterioles as a consequence of blockade of postsynaptic alpha 1-adrenoceptors. Furthermore, unlike some other alpha-blockers, this lowering of blood pressure is rarely associated with reflex tachycardia or postural hypotension. Therapeutic trials have shown indoramin to be effective in lowering blood pressure in all grades of hypertension: mild and moderate hypertension when used alone, but generally in combination with a thiazide diuretic, and in moderate to moderately severe hypertension when used in combination with a beta-blocker and diuretic. In a few small comparative studies, no significant difference was found in the blood pressure lowering effects between indoramin and methyldopa, propranolol and prazosin. Side effects were similar for indoramin, propranolol and methyldopa; however in the 1 comparative study with prazosin, prazosin produced a lower incidence of sedation. Indeed, the most common side effect with indoramin therapy has been sedation of a mild to moderate and/or transient nature, reported in about 19% of cases. Other side effects which have sometimes led to a withdrawal of indoramin treatment have been dry mouth, dizziness, and in males, failure of ejaculation; however, side effects may be reduced by starting therapy with smaller doses and titrating more gradually.