Asthma exacerbations during long term â agonist use: influence of â2 adrenoceptor polymorphism

Background—Polymorphisms of the â2 adrenoceptor influence receptor function in vitro and asthma phenotypes in vivo. However, their importance in determining responses to inhaled â agonist treatment has not been clearly defined. Methods—In a retrospective analysis of previously published data we have examined relationships between polymorphisms at codons 16 and 27 of the â2 adrenoceptor and clinical outcomes in a randomised, placebo controlled, crossover trial of regularly scheduled salbutamol and salmeterol in 115 patients with mild to moderate asthma. Genotyping was obtained for positions 16 and 27 in 108 and 107 patients, respectively. For position 16, 17 patients (16%) were homozygous ArgArg, 40 (37%) were heterozygous Arg-Gly, and 51 (47%) were homozygous Gly-Gly. Results—Within the homozygous Arg-16 group major exacerbations were more frequent during salbutamol treatment than with placebo (1.91 (95% CI 1.07 to 3.12) per year versus 0.81 (95% CI 0.28 to 1.66) per year; p = 0.005). No significant treatment related diVerences occurred for heterozygous Arg-Gly patients (salbutamol 0.11 (95% CI 0.01 to 0.40), placebo 0.54 (95% CI 0.26 to 1.00) exacerbations per year) or homozygous Gly-16 patients (salbutamol 0.38 (95% CI 0.17 to 0.73), placebo 0.30 (95% CI 0.12 to 0.61) exacerbations per year). No adverse changes occurred for any position 16 subgroup with salmeterol. There was no significant relationship between position 27 genotypes and treatment related outcomes. Conclusion—Homozygous Arg-16 patients are susceptible to clinically important increases in asthma exacerbations during chronic dosing with the short acting â2 agonist salbutamol. (Thorax 2000;55:762–767)