Inhaled rifampicin powder formulations and their in vivo studies for clinical application in tuberculosis treatment
Background Tuberculosis (TB), a global health problem caused by Mycobacterium tuberculosis, mainly affects the lungs and spreads to other organs. Rifampicin is a potent anti-TB drug, but its oral delivery results in low drug concentrations in the caseating lung lesions, affecting its bactericidal activity that may lead to treatment failure, relapse and emergence of bacterial resistance. To increase the drug concentration in the lung lesions and the systemic circulation, high-dose rifampicin has been tested clinically via the oral route. However, high oral doses of rifampicin are associated with increased risk of systemic toxicity. Pulmonary delivery is a promising alternative to achieve high drug concentration in the lungs as well as the systemic circulation using lower doses compared to the oral route. Purpose The work described in this thesis was aimed at development of high-dose rifampicin powder formulations for inhaled anti-TB therapy, their in vitro characterization, and in vivo assessment of safety and pharmacokinetics after intra-tracheal administration in a rat model. We hypothesized that intra-tracheal administration of high-dose powder formulations of rifampicin would be safe to rat lungs and the liver, and result in higher systemic bioavailability compared to the oral administration at same dose. Methods High-dose powder formulations of rifampicin for inhalation were prepared using spray drying and crystallization methods. X-ray powder diffraction (XRD) was used to determine the crystallinity of the powders. A next generation impactor (NGI) was used to study the in vitro aerosolization behaviour. In vitro dissolution test was performed using a custom-made apparatus. The in vivo safety and pharmacokinetics of high-dose intra-tracheal rifampicin was studied in Sprague Dawley rats. High-dose rifampicin was administered by either intra-tracheal powder insufflation (25 and 50 mg/kg) or oral gavage (50 mg/kg). Following single and repeated administration of rifampicin, safety to rat lung and liver was evaluated by histopathology. Serum alanine transaminase (ALT) and aspartate aminotransferase (AST) assays were performed to study the hepatic effects. For pharmacokinetic evaluation, rifampicin quantification in plasma was carried out by liquid chromatography mass spectrometry (LC-MS/MS) at predetermined time points after drug administration on day 0 and day 6. Results Spray drying yielded amorphous powder formulation of rifampicin (RIF A) while crystalline pentahydrate (RIF C1 and RIF C2) and dihydrate (RIF C3) powder formulations were obtained by crystallization. All formulations had a mean particle size smaller than 3.8 μm and a fine particle fraction higher than 58.0%. RIF A and RIF C3 were selected for in vivo studies due to their rapid in vitro dissolution compared to RIF C1 and RIF C2. Intra-tracheal administration of rifampicin resulted in significantly lower serum ALT activity and similar AST activity compared to oral administration, suggesting reduced drug burden on the liver after pulmonary administration. Repeated intra-tracheal administration of rifampicin was well tolerated by rats, and the lung and hepatic architecture was normal upon histopathological evaluation. Rifampicin bioavailability after intra-tracheal RIF A (AUC0-∞ = 193.1 ± 37.9 μg.h/mL) was significantly higher compared to that from its oral administration (AUC0-∞ = 87.4 ± 64.7 μg.h/mL) at same dose. Increasing the intra-tracheal dose resulted in a more than dose proportional bioavailability suggesting nonlinear pharmacokinetics of inhaled rifampicin. Conclusions The amorphous and the crystalline dihydrate rifampicin formulations are suitable for inhaled high-dose delivery of rifampicin in TB treatment. A high concentration of rifampicin in the lungs and the systemic circulation at a relatively low administered dose can be achieved by pulmonary administration of rifampicin, either alone or in addition to the standard oral dose. By achieving high bioavailability of rifampicin, this approach has the potential to achieve improved bactericidal activity, minimize the development of drug resistance and reduce the duration of TB treatment.
Advisor: Das, Shyamal Chandra; Hill, Philip; Dummer, Jack; Katare, Rajesh
Degree Name: Doctor of Philosophy
Degree Discipline: School of Pharmacy
Publisher: University of Otago
Keywords: Rifampicin; Tuberculosis; Pulmonary drug delivery; Aerosolization; Safety and pharmacokinetics; Inhalation; Amorphous and crystalline
Research Type: Thesis