Absolute and relative bioavailability of a slow release theophylline preparation in asthmatic children

This study was carried out on 14 asthmatic children aged 7-13 years. They all received three preparations (aminophylline by intravenous infusion, lysine theophyllinate orally in solution and slow release theophylline orally as capsules) in a single dose of 100 mg active ingredient in a crossover design. Plasma theophylline concentrations, determined by a fluorescent polarization immunoassay, were evaluated both by compartmental and non-compartmental analysis. After administration of slow release theophylline, its maximum plasma concentration and the time needed to reach this were (±SD) 3.19 ± 0.63 μg/ml and 8.71 ± 2.30 h, respectiely, compared to 4.51 ± 0.94 μg/ml and 1.96 ± 0.85 h, respectively, for the oral normal release solution. Mean absolute and relative percentage bioavailabilities for slow release theophylline in asthmatic children were (±SD) 92.7 ± 23.2% and 83.14 ± 14.69% respectively. These are similar to the values found with other slow release formulations in paediatric patients.