Bronchodilatory and circulatory effects of two doses of a beta2-agonist (terbutaline) inhaled with IPPB in patients with reversible airways obstruction.

A beta2-receptor agonist, terbutaline (Bricanyl), in doses of 2.5 and 5 mg was inhaled by IPPB with a Bird Mark 8 in a double-blind cross-over randomized study on consecutive days in 12 patients with at least 15% reversibility of PEFR or FEV 1.0. One minute after the inhalation of 2.5 mg, PEFR had increased significantly; the greatest effect (+ 34%) was recorded after 120 min. After 5 mg the increase was more marked, with the greatest recorded effect (+ 43%) after 120 min; FEV1 and VC showed similar changes with a tendency towards greater and longer effects after the larger dose. Heart rate did not change. Systolic and diastolic blood pressures decreased at the most with 9 and 5 mmHg respectively, 30 min after 5 mg terbutaline. One patient reported tremor and palpitations 5 min after inhaling 5 mg. Our patients who were treated with beta-adrenergic drugs showed less systemic effects after the same dose of terbutaline than previously non-treated normal subjects in an earlier study. This may support recent findings of drug-induced tolerance to beta-stimulating agents in the heart and skeletal muscles with preservation of good effect on the airway smooth muscles, here shown as having a good residual bronchodilatory effect with clinically non-important effects on heart rate and tremor.