Plasma concentration and side-effects of terbutaline.

Infusion of terbutaline sulphate (0.25 mg) was followed by increases of plasma insulin and blood glucose concentrations and by a decrease in plasma potassium. Similar metabolic changes were seen on the first day of oral terbutaline administration (5 mg, 3 times daily). Heart rate was moderately increased by terbutaline over the entire period (13 days) of oral dosing. Hand tremor always increased after terbutaline, but to a lesser degree on days 5 and 13 than after the first oral dose. On day 13, there was a very small increase in plasma insulin and no reduction in plasma potassium. Blood glucose increased slightly from an elevated morning value. Plasma terbutaline showed similar maximum concentrations on days 1 and 13. Since the concentration at the effector organs should be at least as high on day 13 as on day 1, these findings indicate that the tolerance was mediated through reduced response of the effector organs.