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The effects of enalapril and spironolactone on terbutaline-induced hypokalemia
A R Rahman1, D G McDevitt, A D Struthers
1Department of Clinical Pharmacology, Ninewells Hospital and Medical School, Dundee, Scotland.
Objective:
To investigate whether enalapril (E) 10 mg and spironolactone (S) 100 mg attenuate the hypokalemic effect of inhaled terbutaline (T).
Design:
Randomized single-blind crossover. Subjects received the following treatment combinations: (a) placebo (P), (b) T alone, (c) T + E, or (d) T + S.
Setting:
University Department of Clinical Pharmacology.
Participants:
Twenty healthy volunteers (ten male, ten female) of mean age 22.8 +/- 3.1 years.
Main Outcome Measures:
Serum potassium, magnesium, ECG changes (R-R interval, T wave, and QTc interval) for 4 h after terbutaline inhalation.
Main Results:
Baseline serum potassium levels were higher following prior treatment with E and S; P, 3.78 mmol/L (3.67 to 3.88); T + E, 3.93 mmol-1 (3.82 to 4.03); and T + S, 4.03 mmol/L (3.93 to 4.14) (p less than 0.05). Mean potassium concentrations over 4 h were also higher following prior treatment with E and S; T, 3.58 mmol/L (3.54 to 3.63); T + E, 3.68 mmol/L (3.64 to 3.72) (p less than 0.05); and T + S, 3.73 mmol/L (3.68 to 3.78) (p less than 0.01).
Conclusions:
Enalapril and spironolactone protect against the fall in serum potassium over 4 h by elevating baseline potassium concentration. These potassium-sparing drugs, however, should not be used to prevent the hypokalemic and electrocardiographic sequelae of inhaled beta 2-agonists.