Pharmacokinetics of Inhaled Rifampicin Porous Particles for Tuberculosis Treatment: Insight into Rifampicin Absorption from the Lungs of Guinea Pigs.

Tuberculosis (TB) is a life-threatening infection that requires a lengthy treatment process that is often associated with adverse effects. Pulmonary delivery of anti-TB drugs has the potential to increase efficacy of treatment by increasing drug concentrations at the lungs, the primary site of infection. The aim of the present study is to evaluate the disposition of rifampicin (RIF) after its pulmonary administration as porous particles (PPs) to guinea pigs and contrast it to that after oral administration. RIF microparticles were prepared by spray drying a solution of RIF and L-leucine (9:1), and the resulting particles were characterized for their physicochemical properties. Animals received RIF either as intravenous solution (iv), as oral suspension of micronized RIF (ORS) and RIF-PPs (ORPP), or by insufflation of the PPs (IRPP). Plasma samples were collected at preselected time points, and bronchoalveolar lavage (BAL) was performed at the end of the study. RIF concentrations in biological samples were analyzed by HPLC. Plasma concentration versus time data was analyzed by compartmental and noncompartmental methods. RIF PPs were thin walled porous particles with mass median aerodynamic diameter (MMAD) of 4.8±0.1 μm, GSD=1.29±0.03, and fine particle fraction below 5.8 μm of 52.9±2.0%. RIF content in the resulting particles was 91.8±0.1%. Plasma concentration vs time profiles revealed that the terminal slope of the iv group was different from that of the oral or pulmonary groups, indicating the possibility of flip-flop kinetics. RIF from IRPP appeared to be absorbed faster than that of ORPP or ORS as evidenced by higher RIF plasma concentrations up until 2 h. Notably, similar AUC (when corrected by dose), similar CL, λ, and half-life were obtained after oral administration of RIF at 40 mg/kg and pulmonary administration of RIF at 20 mg/kg. However, RIF in the IRPP group had a shorter Tmax and higher bioavailability than orally dosed groups. In addition, RIF concentrations in the BAL of animals in the IRPP group were 3-4-fold larger than those in the orally dosed groups. The disposition in ORS and ORPP were best described by a model with two sequential compartments, whereas the disposition of IRPP was best described by a two parallel compartment model. The advantages of delivering RIF by the pulmonary route are demonstrated in the present study. These include achieving higher RIF concentrations in the lungs and similar systemic levels after pulmonary delivery of one-half of the oral nominal dose. This is expected to result in a more effective treatment of pulmonary TB, as shown previously in published efficacy studies.