Population pharmacodynamic model of bronchodilator response to inhaled albuterol in children and adults with asthma

Background: Because interpatient variability in bronchodilation from inhaled albuterol is large and clinically important, we characterized the albuterol dose/response relationship by pharmacodynamic modeling and quantified variability. Methods: Eighty-one patients with asthma (24% African American [AA]; 8 to 65 years old; baseline FEV₁, 40 to 80% of predicted) received 180 μg of albuterol from a metered-dose inhaler (MDI), and then 90 μg every 15 min until maximum improvement or 540 μg was administered; all then received 2.5 mg of nebulized albuterol. FEV₁ was measured 15 min after each dose. The population cumulative dose/response data were fitted with a sigmoid maximum effect of albuterol (Emax) [maximum percentage of predicted FEV₁ effect] model by nonlinear mixed-effects modeling. The influence of covariates on maximum percentage of predicted FEV₁ reached after albuterol administration (Rmax) and cumulative dose of albuterol required to bring about 50% of maximum effect of albuterol (ED₅₀) and differences between AA and white patients were explored. Results: ED₅₀ was 141 μg, and Emax was 24.0%. Coefficients of variation for ED₅₀ and Emax were 40% and 56%, respectively. Ethnicity was a statistically significant covariate (p < 0.05). AA and white patients reached 82.4% and 91.9% of predicted FEV₁, respectively (p = 0.0004); and absolute improvement in percentage of predicted FEV₁ was 16.6% in AA patients vs 26.7% in white patients (p < 0.0003). There were no baseline characteristic differences between AA and white patients. Nebulized albuterol increased FEV₁ ≥ 200 mL in 21% of participants. Heart rate and BP were unchanged from baseline after maximal albuterol doses. Conclusions: Our model predicts that 180 μg of albuterol by MDI produces a 14.4% increase in percentage of predicted FEV₁ over baseline (11.7% in AA patients, and 17.5% in white patients). Emax varies widely between asthmatic patients. AA patients are less responsive to maximal doses of inhaled albuterol than white patients.