Comparison of hypokalaemic, electrocardiographic and haemodynamic responses to inhaled isoprenaline and salbutamol in young and elderly subjects.

The purpose of the study was to compare beta-adrenoceptor responsiveness to salbutamol (beta-2 selective agonist) and isoprenaline (non-selective) in young (n = 10, age 23 y) and elderly (n = 7, age 71 y) subjects. Subjects were given cumulative doubling doses of inhaled isoprenaline or salbutamol (500-4000 micrograms), and placebo, in a single-blind randomised cross-over design. Plasma potassium, electrocardiographic (R-R, T-wave, Q-Tc) and blood pressure responses were measured at baseline and at each dose step. There were no difference between baseline values for each of the three study days within each group of subjects. Hypokalaemia was significantly greater in response to salbutamol compared with isoprenaline in both the young (as change from baseline): -0.61 versus -0.10 mmol.l-1: and in the elderly: -0.68 versus -0.20 mmol.l-1. There were no differences between young and elderly responses. T-wave amplitude fell significantly in response to isoprenaline and salbutamol, although this effect was progressively attenuated with increasing doses of isoprenaline. Maximum T-wave response (change from baseline) was greater with salbutamol than isoprenaline in the young: -0.22 versus -0.11 mV: and in the elderly: -0.17 versus -0.08 mV, and there were no differences between the two groups. There were no differences between the effects of isoprenaline and salbutamol on Q-Tc prolongation or heart rate. Chronotropic responses to salbutamol were greater in the elderly: 39 versus 24 beats.min-1. There were larger increases in SBP with isoprenaline in both groups. Falls in DBP in response to isoprenaline and salbutamol were significantly greater in the elderly.(ABSTRACT TRUNCATED AT 250 WORDS)