Dose-related protection against histamine-induced bronchoconstriction by inhaled salmeterol.

A double-blind crossover study was carried out in 8 subjects to compare the effect of inhaled salmeterol 12.5, 50 and 100 micrograms with inhaled salbutamol 200 micrograms on resting lung function and on bronchoconstriction in response to inhaled histamine up to 12 hours following each treatment. Changes in resting lung function were measured using forced expiratory volume in one second (FEV1) and flow at 70% of vital capacity taken from partial expiratory flow volume curves (pEFR70). The concentrations of histamine which produced a 15% fall in FEV1 (PC15) and a 40% fall in pEFR70 (PC40) were also measured. The peak bronchodilator effect after salmeterol 50 and 100 micrograms was similar in magnitude to salbutamol 200 micrograms. Salmeterol produced dose-related changes in lung function and protection against histamine-induced bronchoconstriction. The duration of the effect of salmeterol (50 and 100 micrograms) was longer than that for salbutamol (200 micrograms). Although pEFR70 is a more sensitive measure of lung function there was no greater separation between different doses of salmeterol than with FEV1. Both salmeterol and salbutamol were well tolerated.

Salmeterol, a novel, long-acting beta 2-adrenoceptor agonist: characterization of pharmacological activity in vitro and in vivo.

1. Salmeterol, a novel, long-acting beta-adrenoceptor agonist, has been compared with isoprenaline and salbutamol for activity in vitro on a range of beta-adrenoceptor containing preparations from laboratory animals and man, and in vivo for bronchodilator activity in the conscious guinea-pig. 2. Salmeterol, like isoprenaline and salbutamol, relaxed preparations of both guinea-pig trachea (contracted by prostaglandin (PG)F2alpha or electrical stimulation) and human bronchus (contracted by PGF 2 alpha) in a concentration-related fashion. Salmeterol was of similar potency to isoprenaline and more potent than salbutamol on both airway preparations. 3. Relaxant responses of superfused guinea-pig trachea and human bronchus to isoprenaline and salbutamol declined rapidly when the agonists were washed from the tissues, with complete recovery within 10 min, whereas responses to salmeterol were more persistent. In electrically-stimulated guinea-pig trachea preparations, inhibition by salmeterol persisted for periods of up to 12h, despite continuous superfusion with agonist-free medium. However, these persistent responses were rapidly and fully reversed by the beta-adrenoceptor blocking drug, propranolol (0.1 microM). In further studies on guinea-pig trachea, propranolol caused concentration-related parallel, rightward shifts of salmeterol concentration-effect curves, yielding a pA2 of 9.0. The slope of the Schild plot was 1.02. 4. Another beta-adrenoceptor blocking drug, sotalol (10 microM), also fully and rapidly reversed established submaximal responses to salmeterol in superfused guinea-pig trachea. However, after administration of sotalol was stopped, the antagonism waned, and salmeterol responses were reasserted without the addition of further agonist. 5. In the beta 1-adrenoceptor containing preparation, rat left atria, isoprenaline exhibited potent, concentration-related, positive inotropic activity, whereas salbutamol and salmeterol were at least 2000-5000 fold less potent, and appeared to be partial agonists. At a concentration of 72 microM, salmeterol exhibited weak antagonism of isoprenaline-induced increases in atrial force of contraction. This antagonism was less marked than that caused by salbutamol (42 microM).6. On the guinea-pig isolated gastric fundus strip, a putative beta3-adrenoceptor containing preparation, salbutamol and salmeterol had only modest agonist activity, being 20-30 fold less potent than isoprenaline and the selective ,beta3-adrenoceptor agonist, BRL 35135.7. In conscious guinea-pigs, inhaled salmeterol and salbutamol were approximately equipotent in causing dose-related bronchodilatation. Whereas the duration of action of salbutamol at its threshold-effective dose was less than 90min, the responses to a similarly effective dose of salmeterol were well-maintained for at least 6 h.8. Salmeterol is therefore a potent and selective beta2-adrenoceptor agonist with a remarkably long duration of action in isolated superfused airways smooth muscle. It also causes persistent bronchodilatation in vivo, in the guinea-pig, when administered by the inhaled route.