Eight patients with exercise-induced asthma participated in a single blind doseduration study comparing the protective effect of inhaled sodium cromoglycate (SCG) in increasing concentrations from 2 to 40 g/l. Saline was used as a control. Effects were assessed from the mean maximal fall in forced expiratory volume in 1 sec (FEV1) after running on a treadmill for 8 min at 20, 150 and 270 min after drug administration There was no significant difference between the mean baseline values of FEV1, before and after inhalation of saline and SCG on 4 days of exercise testing. In addition, the maximal percentage falls in FEV1 in the three control exercise tests carried out at 20, 150 and 270 min after inhalation of saline were also comparable. The mean percentage fall in FEV1, (s.e.m.) after saline, SCG 2 g./l, SCG 20 g/l and SCG 40 g/l were 29.3 (4.4). 11.7 (4.5), 8.3 (3.1) and 9.4 (2.3) respectively in the first test at 20 min and 24.5(5.1), 14.9 (4.2), 13.1 (2.5)and 13.7 (2.8) respectively in the second test at 150 after treatment. The inhibitory effect of SCG was statistically significant at all the concentrations used and the protection offered by the three concentrations of SCG was comparable. In the third exercise test at 270 min after treatment, the mean maximum percentage change after saline. SCG 2 g/l, SCG 20 g/l and SCG 40 g/l were 26-1 (4.8), 23.0 (6.1), 16.6 (5 0) and 15.8 (4.7) respectively. A partial protection in exercise-induced fall in FEV1 was observed with 20 g/l and 40 g/l whereas the effect of SCG at 2 g/l had worn off by this time.
This study demonstrates that SCG when given by nebulization is effective in exercise-induced asthma throughout the dose range currently used clinically. However, the protection with the lowest dose does not last beyond 2 hr. It is therefore important to adjust the frequency and timing of drug administration with different methods.