Sex differences in hypokalaemic and electrocardiographic effects of inhaled terbutaline.

BACKGROUND Gender differences in the chronotropic effects of infused isoprenaline have previously been described. The aim of the present study was to investigate possible gender differences in hypokalaemic, chronotropic, and electrocardiographic effects of inhaled terbutaline. METHODS Twenty healthy volunteers (10 female) were recruited (mean age 24 years for women (F) and 22 years for men (M). Subjects were given either inhaled terbutaline 5 mg or placebo in single blind, randomised crossover fashion and the following measurements were made for four hours after inhalation: (a) serum potassium concentration; (b) heart rate; (c) electrocardiographic sequelae (T wave amplitude, Q-Tc interval). The effects of terbutaline on serum potassium was chosen as the primary end point for detecting a 0.3 mmol/l difference between sexes, with a beta error of 0.2 and alpha set at 0.05. RESULTS The hypokalaemic effects of terbutaline were significantly greater in women, the potassium results (means and 95% CI) being as follows: lowest potassium concentration--F 3.12 (2.96-3.28) mmol/l v M 3.65 (3.49-3.81) mmol/l; percentage change from baseline at one hour--F 15.4% (11.5-19.3%) v M 8.5% (4.6-12.3%); average potassium concentration during the four hours--F 3.39 (3.33-3.46) mmol/l v M 3.78 (3.72-3.85) mmol/l. There was no significant regression between body weight and the potassium response to terbutaline. There were also significant sex differences for T wave, Q-Tc, and heart rate response. The percentage fall in T wave amplitude 30 minutes after terbutaline was: F 44.6% (32.1-57.0%) v M 22.4% (9.9-34.8%). CONCLUSIONS Women are more sensitive to the hypokalaemic, chronotropic, and electrocardiographic sequelae of inhaled terbutaline.