Does Theophylline Potentiate Inhaled β2‐Agonists?

The influence of pretreatment with equipment bronchodilating doses of intravenous theophyllamine and inhaled terbutaline on the effect of five terbutaline inhalations was investigated in a cross-over study in six adult asthmatics with stable and reproducible bronchoconstriction. Theophylline in a dose giving a maximal mean plasma concentration of 16.7 +/- 1.21 micrograms/ml (92 mumol/l) gave far from maximal acute bronchodilation as the following five terbutaline inhalations gave the same further bronchodilation. Pretreatment with five terbutaline inhalations induced almost equal bronchodilation compared with theophyllamine but the following five inhalations now gave only about one-fourth of the effects recorded after theophyllamine pretreatment. This potentiation could, however, be due to the different routes of administration of the pretreatments. In a randomized, double-blind, cross-over study in eight asthmatic, pretreatment with equipotent oral bronchodilating doses of theophylline and terbutaline was shown to give the same potentiation of the following five terbutaline inhalations. Theoyphylline orally as such thus did not potentiate the effect of inhaled beta 2-stimulants. It had only the same effect as oral terbutaline, but induced less tremor. This means that the potentiation after intravenous and oral pretreatment was not due to theophylline but to the different routes of administrations. Systemic administration probably gave a better distribution and thus better effect of the inhaled terbutaline.