Potassium and Magnesium Distribution, ECG Changes, and Ventricular Ectopic Beats During β2-Adrenergic Stimulation With Terbutaline in Healthy Subjects

Objective: To study the effect of intravenous (IV) terbutaline on potassium (K) and magnesium (Mg) distribution, ECG changes, and prevalence of ventricular ectopic beats in healthy subjects. Design: Randomized double-blind, placebo-controlled crossover. Subjects received either placebo or terbutaline (bolus, 0.25 mg; maintenance dose, 5 µg/min). Setting: University Department of Clinical Chemistry. Participants: Ten healthy male volunteers. Mean age was 24.1 (range, 20 to 31) years. Main outcome measures: Serum potassium and magnesium, muscle potassium and magnesium, and muscle sodium-potassium pump number. Urinary excretion of potassium and magnesium. ECG changes (T-wave and QTC interval) and the number of ventricular ectopic beats. Main results: Terbutaline produced an immediate decrease in serum potassium level from 4.17 (4.04 to 4.30) mmol/L to a nadir of 3.32 (3.06 to 3.58) mmol/L (p