Bioavailability of Theophylline from Three Different Tablets in Asthmatic Patients and Their Bronchodilating Effects in Combination with Terbutaline Inhalation

The bioavailability of three different theophylline tablets (microcrystallinic theophylline, Theolair®, Nuelin®, 3M Riker), choline theophyllinate as a new film‐coated tablet (Teovent®, Ferrosan, Sweden) and theophyllaminopropanol (Oxyphylline® Draco, Sweden) was investigated in eight adult asthmatics in a randomized, double‐blind, cross‐over study.Effects on ventilatory capacity (FEV1 and FVC), circulation (heart rate and blood pressure) and skeletal muscle tremor were followed. The theophylline concentration was determined by gas chromatography. Forty‐five minutes after theophylline administration the plasma concentrations were almost the same for all four formulations. The bioavailability was also almost identical. The half‐life for intravenous theophylline in these asthmatics was 7.4 ± 0.64. The three tablet formulations had equal effect on FEV1 and the effect was sustained throughout the 6‐h period.Six hours after theophylline administration five terbutaline inhalations induced the same further increase in FEV1. The results indicate that theophylline alone has only a moderate acute bronchodilating effect at recommended plasma concentrations but gives a good effect when combined with inhaled β2‐adrenostimulants.