Relationship between bronchial effects and plasma practolol concentration in man.
A double-blind, balanced and randomised study in 8 healthy volunteers examined the effects of relatively high versus low single doses of practolol on heart rate and ventilation at rest and during standardised exercise. Practolol 1 and 4 mg/kg, a typically non-selective drug propranolol 0.2 mg/kg, and placebo were given intravenously at weekly intervals. Cardiac beta-adrenoceptor blockade was measured by the reduction in exercise heart rate greater than 160 beats/min, and bronchial beta-adrenoceptor blockade by the reduction in exercise peak expiratory flow rate (PEFR) up to 4 h after each treatment. Results were assessed by analysis of co-variance. All three active treatments reduced exercise heart rate markedly, practolol 4 mg/kg causing most reduction. Exercise PEFR was significantly reduced by propranolol 0.2 mg/kg compared with both practolol 1 mg/kg and placebo at all times of measurement, and by practolol 4 mg/kg compared with practolol 1 mg/kg and placebo at most times. Mean plasma concentrations after practolol 4 mg/kg were 3.5 to 4.5 times higher than after 1 mg/kg. Practolol may lose its 'cardioselectivity' and cause airflow obstruction at relatively high plasma concentrations above about 2 microgram/ml.
D000328:Adult; D000403:Airway Resistance / Q000187:drug effects*; D001980:Bronchi / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010366:Peak Expiratory Flow Rate; D005082:Physical Exertion; D011217:Practolol / Q000097:blood / Q000494:pharmacology*; D013997:Time Factors
D011217:Practolol