A Comparison of Metoprolol and Propranolol on Blood Pressure and Respiratory Function in Patients with Hypertension

Summary: The effects on blood pressure and airway function of the chronic oral administration of two beta blocking agents, propranolol and metoprolol, were studied. Mean arterial pressure (MAP) fall was maximum with 160 mg of propranolol daily (‐12 mmHg , P < 0 05) and 100 mg of metoprolol (‐9 mmHg , P < 0 05) and MAP did not fall further with an increase in dose of either drug. Nine of ten patients whose lung function was assessed showed a change in airway function, with a mean fall in maximal mid‐expiratory flow rate (MMFR) of 05 litres per second (I.sec ‐1 ) on propranolol and 0–36 I.sec ‐1 on metoprolol. The fall was not related to smoking or to atopic status. These data support the hypothesis that there is resting beta adrenergic bronchodilator activity in non‐asthmatic subjects. This activity can be blocked by chronic oral administration of beta blocking drugs. The fall in MMFR in subjects with prior but unrecognized obstruction in the small airways may be sufficient to cause severe malfunction and these drugs should be used with caution in patients with chronic airways obstruction. The fall in MMFR was reversed by salbutamol while the patients were taking metoprolol, but not while they were taking propranolol, suggesting that propranolol has greater affinity than metoprolol for the bronchial beta adrenergic receptors.