Effects of xamoterol a new beta-adrenoceptor partial agonist, in patients with angina pectoris

The xamoterol experience in the treatment of heart failure

Beta blockers may benefit patients with dilated cardiomyopathy but low output failure can be a problem. Thus a beta 1-selective beta blocker with about 45% intrinsic sympathomimetic activity (ISA), such as xamoterol, was thought to have a desirable pharmacologic profile. Long-term studies of xamoterol in patients with idiopathic dilated cardiomyopathy have shown improved cardiac performance and exercise tolerance, while exercise heart rate, left ventricular ejection fraction, and pulmonary artery wedge pressure were decreased. This improvement in exercise capacity and overall quality of life in patients treated with xamoterol has been confirmed in further controlled trials of patients with mild-to-moderate heart failure (NYHA class I and II). However, in patients with moderate-to-severe heart failure (NYHA class III and IV), mortality was unfavorably influenced by xamoterol. The therapeutic role of xamoterol in patients with heart disease needs further refinement.

Beta receptor antagonists in the treatment of heart failure

The use of beta-receptor antagonists in the treatment of heart failure is controversial. Available data do not allow general recommendations regarding their use. In dilated cardiomyopathy, several studies suggest that long-term treatment in individual patients reduces symptoms and increases exercise capacity. Short-term treatment is usually not beneficial, except in patients with ischemically induced left ventricular dysfunction. In heart failure, post myocardial infarction and in chronic ischemic heart disease, no proper long-term study has been performed to evaluate its effects. However, patients with acute myocardial infarction tolerate beta blockers, despite the presence of left ventricular dysfunction and long-term prognosis is improved. Newer agents, some with ancillary properties, such as intrinsic activity and vasodilatation, may have advantages. In the future we need a better description of the cardiac status in our patients in order to be able to select those that will respond favorably to beta-receptor antagonists. The mechanisms by which some patients improve are still obscure. Protection against receptor downregulation, restoration of receptor density, protection against cardiotoxicity of catecholamines, and improvement in ischemic systolic and diastolic left ventricular function are all possible. The fear that beta-receptor antagonists are dangerous in heart failure is in most instances not warranted, but an initial deterioration may have to be accepted in order to gain long-term beneficial effects. Ongoing studies in both idiopathic cardiomyopathy and in postinfarction failure will hopefully help us to define the use of beta-adrenoceptor antagonists in the future.

Effects of xamoterol in acute myocardial infarction: blood pressure, heart rate, arrhythmias and early clinical course

Xamoterol is a novel partial agonist of beta 1 adrenoceptors that reduces myocardial ischaemia and improves ventricular function in patients with mild to moderate heart failure. In a double blind, randomised, placebo controlled study, the effects of xamoterol given in a dose of 200 mg twice daily were studied in 51 consecutive patients with acute myocardial infarction, including 17 receiving diuretics for left ventricular failure. Treatment was started on the third day of admission and continued for 7 days. Blood pressure was recorded at 0900 daily, and 24 hour ambulatory electrocardiogram monitoring was commenced at this time on days 1 (pre-treatment), 4, 6 and 9 of admission. Additional drug therapy was recorded daily throughout the study. One patient died prior to randomisation and three were withdrawn (1 placebo, 2 xamoterol) with ventricular arrhythmias and/or disturbances of conduction. Compared to placebo, xamoterol had no effect on the rate of ventricular premature beats or ventricular tachycardia. Xamoterol increased nocturnal heart rate (0000-0600 hrs 79 +/- 2; placebo 72 +/- beats/min; P less than 0.03) but did not change blood pressure. Three patients receiving xamoterol, and 7 on placebo, required new (after randomisation) antianginal therapy. One patient treated with placebo developed new heart failure. These results show that xamoterol can be administered safely to selected patients following myocardial infarction, including those treated for mild heart failure.

Ischaemic left ventricular failure: evidence of sustained benefit after 18 months' treatment with xamoterol

The long term effects of treatment with xamoterol in 14 patients aged 44-73 with mild to moderate heart failure as a result of ischaemic heart disease are reported. After 18 months' treatment with xamoterol, patients were assessed in a randomised double blind crossover comparison of xamoterol (200 mg twice a day) and placebo, each given for one month. Compared with placebo, xamoterol significantly increased exercise duration and work done on a bicycle ergometer and reduced the maximum exercise heart rate. Assessment of symptoms and activities at 12 months by visual analogue and Likert scales showed a trend towards the relief of symptoms of breathlessness and tiredness and an improvement in activity. There was an improvement in the clinical signs of heart failure and no haemodynamic deterioration over a 12 month period as assessed by ejection fraction. The improvement in exercise tolerance, symptoms, and activities was sustained for 18 months without side effects or development of tolerance.

Exercise capacity, arrhythmias, humoral and chemical parameters during long-term therapy with xamoterol

In order to assess potential harmful effects of the partial beta-1 agonist xamoterol during long-term therapy, we randomly assigned 30 patients with coronary arterial disease and heart failure in classes II and III of the classification of the New York Heart Association to 200 mg of xamoterol twice daily or placebo during a treatment period of 3 months. A supine bicycle exercise test was performed at baseline and after three months in order to assess changes of exercise capacity. Blood samples for determination of creatinine, electrolytes, renin and norepinephrine were withdrawn simultaneously. Twenty-four hour ambulatory Holter electrocardiograms were performed before study, at the end of the study and 72 hours after withdrawal of study medication. On xamoterol, exercise capacity increased from 21.9 +/- 9.7 to 27.8 +/- 14.8 kilojoule (P = 0.032) compared to baseline levels. Exercise duration increased from 340 +/- 115 to 400 +/- 144 seconds (P = 0.043). Heart rate decreased by 10% (P = 0.05) at the 50 watt level and by 10% (P = 0.024) on maximum exercise compared to the baseline values. The rate pressure product was unchanged at rest and dropped by 11% (P = 0.038) on maximum exercise. In contrast, on placebo no significant changes occurred. During xamoterol therapy no changes of blood pressure, electrolytes, renal function and the time-intervals of electrocardiogram were observed. Xamoterol did not enhance arrhythmias during 24-hour ambulatory Holter monitoring. No serious side effects were observed. Xamoterol would appear to be a suitable and safe drug in the therapy of mild to moderate heart failure.

Xamoterol recruits an inotropic reserve in the acutely failing, reperfused canine myocardium without detrimental effects on its subsequent recovery

The present study tested (1) whether xamoterol recruits an inotropic reserve in reperfused myocardium and (2) whether acute inotropic stimulation by xamoterol has deleterious consequences on the long-term recovery of the reperfused myocardium. Sixteen anaesthetized, open-chest dogs were bilaterally vagotomized and heart rate kept constant by left atrial pacing. The distal left circumflex coronary artery was occluded for 15 min and then reperfused for 8 h. The coronary occlusion resulted in regional myocardial dyskinesia and myocardial function remained severely depressed after release of the occlusion. At 10 min reperfusion, 8 dogs received xamoterol (100 micrograms/kg i.v.), whereas the remaining 8 dogs served as controls and received saline. Xamoterol increased mean systolic wall thickening velocity (from 1.47 +/- 2.34 (SD) mm/s at 10 min reperfusion to 7.13 +/- 3.55 mm/s at 30 min reperfusion and 7.64 +/- 2.48 mm/s at 1 h reperfusion, respectively, both P less than 0.05). In the control group, only a slow recovery of mean systolic wall thickening velocity was observed (from 3.14 +/- 3.30 mm/s to 2.96 +/- 3.74 mm/s and 4.03 +/- 3.00 mm/s at 10 min, 30 min, and 1 h reperfusion, respectively). At 8 h reperfusion, mean systolic wall thickening velocity was similar in both groups (7.97 +/- 4.23 mm/s in the xamoterol-group and 6.87 +/- 4.00 mm/s in the placebo-group). Histological examination revealed no difference in the extent of necrosis between the two groups after 8 h reperfusion. We conclude that (1) xamoterol recruits an inotropic reserve in reperfused myocardium, and (2) this recruitment of an inotropic reserve does not compromise functional recovery and structural integrity of the reperfused myocardium.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of xamoterol on exercise capacity and left ventricular function in angina pectoris and in dilated cardiomyopathy

The present study evaluates the effect of the beta 1 partial agonist xamoterol in patients with coronary artery disease compared to the effect in patients with dilated cardiomyopathy. Nineteen patients with angina pectoris and nine patients with dilated cardiomyopathy received xamoterol 200 mg b.i.d. for 4 weeks in a placebo-controlled double-blind study. The effect was evaluated with a standardized exercise test and radionuclide angiocardiography with determination of global and regional ejection fraction. At rest xamoterol caused no significant changes among the angina patients while global and regional ejection fraction increased among the cardiomyopathy patients. During exercise, when the drug exerts a beta 1-antagonist effect, xamoterol increased the exercise performance among the angina pectoris patients. Fourteen out of 19 patients with angina pectoris were unable to increase their ejection fraction from rest to work due to coronary ischaemia. These 14 patients improved their global ejection fraction during work after xamoterol treatment.

Xamoterol. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use

Xamoterol is a partial agonist at the beta 1-adrenoceptor. Haemodynamic studies indicate that xamoterol moderately increases myocardial contractility, improves diastolic relaxation and lowers left ventricular filling pressure at rest and during moderate exercise. At higher levels of sympathetic activity (e.g. strenuous exercise) it produces negative chronotropic responses whilst the reduced filling pressure is maintained. Studies in patients with mild to moderate chronic heart failure demonstrate an advantage for xamoterol 200mg twice daily over placebo and digoxin with respect to improvement in exercise capacity and symptoms. In limited trials to date the initial response seems to be maintained during periods of up to 12 months. Preliminary small studies suggest that xamoterol is useful in the treatment of some patients with angina pectoris, sinoatrial disease or postural hypotension, although further studies are needed to confirm its clinical role in such patients. Xamoterol appears to be generally well tolerated, but deleterious effects in a small number of patients with asthma, or severe heart failure due to dilated cardiomyopathy indicate the need for cautious use of xamoterol in patients with these diseases. Thus, xamoterol is a promising addition to the drugs available to the physician for treating patients with mild to moderate heart failure although further controlled studies are required to clearly establish its precise role.