Pafenolol, a new beta 1-adrenoceptor antagonist, has been shown in animals to be more selective for beta 1-adrenoceptors than
metoprolol. It was studied in asthmatic patients to evaluate whether it was more selective with respect to circulatory effects and especially whether this selectivity influenced bronchial muscle tone less than
metoprolol, which has been shown to have beta 1-adrenoceptor selectivity similar to that of
atenolol. Intravenous
pafenolol (5 mg and 7.5 mg),
metoprolol (15 mg), and saline were given double-blind at random and thereafter four increasing doses of
terbutaline were given intravenously to seven asthmatic patients with reproducible reversibility of airways obstruction. After the
terbutaline dose-response curve was determined,
terbutaline was inhaled three times in increasing doses. A separately reported exercise study in the same patients showed that 5 mg
pafenolol and 15 mg
metoprolol were equipotent with respect to beta 1-adrenoceptor blockade, whereas 7.5 mg
pafenolol tended to increase the blockade. The reflex
tachycardia on
terbutaline stimulation after
pafenolol was greater than after
metoprolol due to less blockade of beta 2-adrenoceptors in peripheral blood vessels. The bronchial effect of
pafenolol was equal to that of saline, but there was a difference between the
terbutaline dose-response curves after
pafenolol and
metoprolol that caused a rightward shift of the dose-response curve. Thus,
pafenolol was shown to be more beta 1-selective than
metoprolol.