Antibiotic transport across bronchial epithelial cells: Effects of molecular weight, LogP and apparent permeability

The first step in developing a new inhalable formulation for the treatment of respiratory diseases is to understand the mechanisms involved in the absorption of drugs after lung deposition. This information could be important for the treatment of bacterial infection in the lung, where low permeability would probably be beneficial, or a systemic infection, where high permeability would be desirable. The goal of this study was to evaluate the transport of several antibiotics (ciprofloxacin, azithromycin, moxifloxacin, rifampicin, doxycycline and tobramycin) across human bronchial airway epithelium and to study the influence of molecular weight and LogP on the apparent permeability.

The experiments were conducted using Calu-3 cells seeded in the apical compartment of 24-well Transwell® inserts. The antibiotics transport was measured in both apical to basolateral (A-B) and basolateral to apical (B-A) directions and the apparent permeability of each antibiotic was calculated.

The A-B transport of ciprofloxacin and rifampicin was independent of the initial concentration in the donor compartment, suggesting the involvement of active transporters in their absorption. Moxifloxacin, doxycycline, azithromycin and tobramycin presented a low absorptive permeation in the A-B direction, indicating that these substances could be substrate for efflux pumps. Generally, all antibiotics studied showed low permeabilities in the B-A direction.

These findings suggest that the inhalation route would be favorable for delivering these specific antibiotics for the treatment of respiratory infection, compared with present oral or intravenous administration.