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.