DOES TACHYPHYLAXIS OCCUR TO THE NON-PULMONARY EFFECTS OF SALMETEROL

1 The potential for tachyphylaxis to the non-pulmonary effects of salmeterol, a long-acting selective beta(2)-adrenoceptor agonist was investigated in 12 healthy male subjects in a double-blind two period crossover study design. 2 Subjects received cumulative doses of up to 400 mu g (50+50+100+100+100 mu g at 45 min intervals) inhaled salmeterol prior to a 13 day dosing schedule of twice-daily inhaled salmeterol 100 mu g or placebo. Twelve hours after the last dose of salmeterol or placebo, subjects again received cumulative doses of up to 400 mu g inhaled salmeterol. 3 Pulse rate, blood pressure, 12-lead ECG, physiological tremor and peak expiratory flow rate (PEFR) were measured before administration of cumulative doses of salmeterol, at 10, 20, 30 and 40 min after each incremental dose of salmeterol and at 4, 6 and 8 h after the first dose. Blood samples were taken for plasma potassium, magnesium, non-esterified fatty acids (NEFA) and blood glucose concentrations at 20 and 40 min after each dose and at 4, 6 and 8 h after the first dose. 4 Eleven subjects completed the study. One subject withdrew due to beta(2)-adrenoceptor related adverse events. All other adverse events reported were mild in nature. 5 Dose-related changes to the effects of salmeterol on pulse rate, QTc interval, tremor, PEFR, blood glucose and plasma potassium were seen, but there was no dose-related effect of salmeterol on blood pressure, plasma magnesium and NEFA. 6 Tachyphylaxis occurred to the effects of salmeterol on tremor, QTc and blood glucose. There was no tachyphylaxis to the effects on plasma potassium. Changes in baseline readings after salmeterol made interpretation of the effects seen on pulse rate and PEFR difficult to assess.