The effects of pafenolol and metoprolol on ventilatory function and haemodynamics during exercise by asthmatic patients
Pafenolol, a new β1-adrenoceptor antagonist, has been shown in animal studies to be more selective for the β1-adrenoceptor than metoprolol. In a double-blind crossover study in 8 asthmatic patients its effect on heart rate and ventilatory capacity was studied during exercise. Exercise tests on a bicycle ergometer were performed before and 60, 120 and 180 min after i.v. administration of saline, metoprolol 15 mg, and pafenolol 5 and 7.5 mg. Plasma concentration determinations of metoprolol and pafenolol were estimated. Pafenolol 5 mg had the same blocking effect on exercise tachycardia as metoprolol 15 mg, while pafenolol 7.5 mg tended to have a more pronounced effect. On a molar basis the potency ratio for β1-adrenoceptor — mediated effects of the drugs was about 1:3. Systolic blood pressure during exercise showed similar changes. There was a linear relation between the plasma concentration and the effect on exercise tachycardia. During exercise FEV, did not show any significant difference between the treatments, although there was a tendency towards lower values after metoprolol than after saline and pafenolol. After the last exercise test, when the patients inhaled terbutaline (1.25 mg), there was a significant increase in FEV1 after all treatments, but there was a significant difference (14±5%,p<0,05) between the values after metoprolol and saline. The difference was also significant between pafenolol 5 mg and metoprolol (14±4%,p<0.05). This indicates less blockade of β2-adrenoceptors by pafenolol than by metoprolol. Thus, increased selectivity for β1-adrenoceptors was found for pafenolol as compared to metoprolol, which has been previously found to be a β1-adrenoceptor antagonist with the same selectivity as, for example, atenolol.