The biochemical effects of high-dose inhaled salbutamol in patients with asthma.

We have studied the biochemical effects of high doses of inhaled salbutamol in 14 asthmatic patients age 38 years, FEV1 62%. Cumulative doubling doses of inhaled salbutamol were given every 20 min as follows: 100 micrograms, 200 micrograms, 500 micrograms, 1000 micrograms, 2000 micrograms, 4000 micrograms. Plasma glucose, potassium, and magnesium were measured at each step of the dose-response curve. Salbutamol produced significant hypokalaemic and hyperglycaemic effects, but no significant change in magnesium. There were linear log-dose responses for both glucose (r = 0.58) and potassium (r = -0.46). There were wide individual variations in maximum responses to salbutamol 4000 micrograms (as means and 95% confidence intervals): delta glucose 1.46 (0.83 to 2.09) mmol/l, delta potassium -0.38 (-0.64 to -0.12) mmol/l. Thus, hypokalaemic and hyperglycaemic effects may occur with doses of salbutamol similar to those currently used for nebulizer therapy (2.5-5 mg). We postulate that during acute exacerbations of airflow obstruction these changes may be accentuated and become clinically relevant.