Electrocardiographic changes induced by inhaled salbutamol after treatment with bendrofluazide: effects of replacement therapy with potassium, magnesium and triamterene.

1. Twelve normal subjects were given 5 days' treatment with (a) placebo; (b) 5 mg of bendrofluazide; (c) 5 mg of bendrofluazide plus 24 mmol of potassium; (d) 5 mg of bendrofluazide plus 24 mmol of magnesium; (e) 5 mg of bendrofluazide plus 24 mmol of potassium plus 24 mmol of magnesium; (f) 5 mg of bendrofluazide plus 50 mg of triamterene. 2. After each treatment period, subjects were given two doses of inhaled salbutamol (each of 1 mg), and measurements were made 25 min after each dose. 3. Treatment with bendrofluazide plus salbutamol produced a lower absolute level of plasma potassium than salbutamol alone, although the addition of potassium, magnesium or triamterene did not attenuate this effect. Plasma magnesium was unchanged by salbutamol. 4. Salbutamol was associated with significant electrocardiographic effects, including T-wave flattening, Q-Tc interval prolongation and, in some subjects, U-waves and S-T segment depression. 5. Prior treatment with bendrofluazide potentiated the electrocardiographic effects of salbutamol. Supplementation with potassium and magnesium had no effect on electrocardiographic changes, and the addition of triamterene to bendrofluazide only attenuated electrocardiographic responses in some subjects.