Metabolic effects of inhaled fenoterol in normal subjects

Although the hypokalemic effect of inhaled beta 2-adrenergic agonists has been well documented, little is known as to their effect on plasma magnesium. We therefore examined in ten healthy young volunteers the effect of the inhalation of 2 mg of nebulized fenoterol on plasma potassium (Kpl), plasma magnesium (Mgpl), and intraerythrocytic magnesium (MgIE) levels, as well as on plasma insulin and C peptide concentrations, measured before and serially up to 110 min after fenoterol inhalation. In all subjects, fenoterol inhalation caused a reversible reduction in Kpl (range, 0.2 to 1.1 mEq/L), which was progressive, reaching a statistically significant nadir 30 to 60 min following fenoterol inhalation (largest dip in Kpl, 0.55 +/- 0.29 mEq/L; p < 0.05). The nadir in Kpl levels was preceded by a peak in plasma insulin levels in all subjects. No significant changes in Mgpl or MgIE were observed in any of the subjects. We conclude that fenoterol inhaled at a dosage used in clinical practice significantly reduces Kpl but not Mgpl nor MgIE levels in healthy subjects, indicating a lower sensitivity of Mg++ ions to beta 2-adrenergic stimulation than K+ ions. Beta 2-adrenergic-induced insulin secretion probably contributes to the hypokalemic effect of inhaled fenoterol.