PLA Microparticles for Pulmonary Delivery of AntiTB drugs: Biodistribution study

Abstract

A dry powder inhalable (DPI) microparticles comprising anti-tuberculosis drugs incorporated in biodegradable polymers was developed for the treatment of pulmonary tuberculosis (P. Muttil et al. 2007). Poly L-lactic acid (PLA) microparticles incorporating a high payload of rifabutin and isoniazid were fabricated by spray drying (Buchi 190). Microparticles were composed of PLA and the drugs (rifabutin and isoniazid) at a 2:1:1 weight ratio. Microparticles of desired high encapsulation efficiency and sustained release characteristics were produced having a diameter range of 2-10 µm (Malvern Mastersizer 2000). Differential scanning calorimetry (DSC) was carried out to study drug polymer interaction. The time course of tissue biodistribution following a single inhalation dose of microparticles was evaluated. Thirty-two BALB/c mice were divided into groups of four and administered the DPI using an in-house (nose only) apparatus (Kaur et al. 2008; Verma et al. 2008). A validated HPLC method was used for determination of rifabutin and isoniazid in the lungs (target organ), liver and kidneys (major sites of toxicity) at different time-points after inhalation. A comparison was made with mice receiving free drugs (intravenous) at equivalent doses. Deposition of microparticles in lungs of mice following aerosolization was also evaluated. Pharmacokinetic parameters in different organs were calculated using WinNonlin software version 5.2. Area under the concentration-time curve observed (AUC~obs~), C~max~, half-life (t~½~) and clearance (CL) in lungs following inhalation /intravenous administration were:*Rifabutin*: AUC~obs~-96h= 1697.39 ±154.67 (187.63 ±23.93) µg/ml^-1^hr^-1^; C~max~ = 33.42±3.80 (4.17±0.31) µg.ml^-1^; t~½~= 78.08±9.42 (34.00 ±3.31) and Cl= 1.16±.22 (0.68 ±0.45) ml.h^-1^.*Isoniazid*: AUC~obs~-24h= 566.31±123.96 (99.85 ±14.24) µg/ml^-1^hr^-1^; Cmax= 24.02±1.71 (8.16±0.93) µg.ml^-1^; t~½~= 25.88±12.16 (6.45±3.24) h; and Cl= 5.47±1.30 (0.96±0.14) ml.h^-1^.The relative bioavailability of both drugs incorporated in microparticles was significantly higher compared with free drugs. Peak levels of isoniazid and rifabutin in lungs (target organ) were much higher than those in the liver and kidney of mice in case of inhalation as compared to intravenous administration. Inhalation of microparticles resulted in targeting both drugs to the lungs, with the effect being more pronounced in the case of rifabutin than isoniazid. High and prolonged drug concentrations and increased AUC values (~9-fold and ~6 fold increase of rifabutin and isoniazid in case of lungs) with respect to free drugs were observed. Significant decrease in drug concentration was found in the liver and kidneys. Drug levels were maintained above the minimum inhibitory concentration (MIC) in organs through out the study after administration of encapsulated drugs. Based on favorable biodistribution kinetics, these microparticles hold great potential in reducing dosing frequency and toxicity of antituberculosis drugs.