Does Theophylline Potentiate Inhaled β2‐Agonists?

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Abstract
The influence of pretreatment with equipotent bronchodilating doses of i.v. theophylline and inhaled terbutaline on the effect of 5 terbutaline inhalations was investigated in a cross-over study in 6 adult asthmatics with stable and reproducible bronchoconstriction. Theophylline in a dose giving a maximal mean plasma concentration of 16.7 .+-. 1.21 .mu.g/ml (92 .mu.mol/l) gave far from maximal acute bronchodilation, as the following 5 terbutaline inhalations gave the same further bronchodilation. Pretreatment with 5 terbutaline inhalations induced almost equal bronchodilation compared with theophylline, but the following 5 inhalations now gave only .apprx. 1/4 of the effects recorded after theophylline pretreatment. This potentiation could be due to the different routes of administration of the pretreatments. In a randomized, double-blind, cross-over study in 8 asthmatics, pretreatment with equipotent oral bronchodilating doses of theophylline and terbutaline gave the same potentiation of the following 5 terbutaline inhalation. Theophylline orally did not potentiate the effect of inhaled .beta.2-stimulants. It had only the same effect as oral terbutaline but induced less tremor. The potentiation after i.v. and oral pretreatment was not due to theophylline but to the different routes of administration. Systemic administration probably gave a better distribution and better effect of the inhaled terbutaline.