Calculation of the antibiotic level in the lung tissue and bronchial secretion with an oral controlled-release dosage form.

The drug level-time history in plasma and lung tissue was calculated with an antibiotic orally delivered in either an immediate-release or a controlled-release dosage form. The drug profiles were compared with experiment results given in the literature. In the same way, the drug level was evaluated in the bronchial secretion in contact with lung tissue. A numerical model, based on finite differences taking all the known facts into account was built and tested with the data found in the literature. Transport of the drug was looked at, including a stage of diffusion through the thickness of the lung tissue and a stage of convection into the bronchial secretion. A few parameters were thus considered, including the thickness of the lung tissue and the diffusivity of the antiobiotic through the tissue, the thickness of the bronchial secretion and the coefficient of convective transport into the sputum which characterizes its viscosity. Two partition factors were also introduced for the drug: between the tissue and the serum and between the lung tissue and the bronchial secretion.