Metoprolol Isoproterenol

The use of selective P-antagonists for treatment of CHF has included the P -blocker metoprolol (Table 1) and results of clinical trials suggest long-term beneficial effects. Selective P -antagonists have also been tested, an example of which is xamoterol [81801 -12-9], C2 H25N20, which is (i)-A/-(2-hydroxy-3-(4-hydroxyphenoxy)propylamino)ethylmorphine-4-carboxamide. Xamoterol exhibits approximately 50% of the activity of isoproterenol, and serves to provide modest inotropic effects (128,129). 

A. Both sets of responses to isoproterenol are mediated by p-adrenoceptors, and all the choices are p-antagonists. However, drug X is more effective in antagonizing cardiac responses to isoproterenol than it is the bronchiolar responses. Drug X is therefore a cardioselective p-blocker, that is, selective for Pi over P2 receptors. Metoprolol is the only pi-selective antagonist among the choices. 

A drug useful in the treatment of asthma but lacking bronchodilator action, is (A) Cromolym Ephedrine Isoproterenol Metaproterenol Metoprolol... 

A 64-year-old woman was treated for hypertrophic cardiomyopathy with amiodarone 1.2 g daily and atenolol 50 mg daily. Five days later the atenolol was replaced by metoprolol 100 mg daily. Within 3 hours she complained of dizziness, weakness and blurred vision. On examination she was found to be pale and sweating with a pulse rate of 20 bpm. Her systolic blood pressure was 60 mmHg. Atropine 2 mg did not produce chronotropic or haemodynamic improvement. She responded to isoprena-line (isoproterenol). Severe hypotension has been reported in another patient taking sotalol when intravenous amiodarone (total dose 250 mg) was given. Another report describes cardiac arrest in one patient on amiodarone, and severe bradycardia and ventricular fibrillation (requiring defibrillation) in another, within 1.5 and 2 hours of starting to take propranolol. ... 

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