We wanted to assess the protective effects on
exercise-induced asthma as well as the clinical efficacy and safety of increasing doses of a new
sustained-release formulation of
terbutaline sulphate, in 17 asthmatic children aged 6-12 yrs (mean 9 yrs). Placebo, 2, 4 and 6 mg
terbutaline were given b.i.d. for 14 days, in a randomized, double-blind, cross-over design. At the end of each two week period, an exercise test was performed and plasma
terbutaline was measured. Compared with placebo, no significant effect was seen on
asthma symptoms monitored at home, or on
exercise-induced asthma. The percentage falls in FEV1 after the exercise test were 36, 35, 27 and 28%, after placebo, 4, 8 and 12 mg terbutaline.day-1, respectively. There was no correlation between plasma
terbutaline and dose of
terbutaline. A small but statistically significant dose-related increase in morning and evening peak expiratory flow (PEF) recordings occurred, but the incidence of side-effects also increased with the dose given. There was a trend towards more side-effects when the high doses were used, and two patients withdrew from the study because of side-effects at this dose. It is concluded that continuous treatment, even with high doses of oral
terbutaline, does not offer clinically useful protection against
exercise-induced asthma.