Drug Release Characteristics and Tissue Distribution of Rifapentine Polylactic Acid Sustained-Release Microspheres in Rabbits after Paravertebral Implantation

BACKGROUND: Rates of drug-resistant tuberculosis (TB) and TB associated with human immunodeficiency virus (HIV) infection have increased dramatically, intensifying challenges in TB control. New formulations of TB treatment drugs that control drug release and increase local drug concentrations will have a significant impact on mitigating the toxic side effects and increasing the clinical efficacy of anti-TB drugs. OBJECTIVES: The aim was to observe the sustained release characteristics of rifapentine polylactic acid sustained-release microspheres in vivo and the accumulation of rifapentine in other tissues following paravertebral implantation. METHODS: This study is a basic animal experimental study that began on July 17, 2014 in the Fifth Affiliated hospital of Xinjiang Medical University. One hundred and eight New Zealand white rabbits (weighing 2.8 - 3.0 kg, male and female, China) were randomly divided into three groups of 36 rabbits each. Blood and tissue samples from the liver, lungs, kidneys, vertebrae, and paravertebral muscle were collected at different time points post-surgery. High performance liquid chromatography (HPLC) analysis with a biological internal standard was used to determine the drug concentrations in samples. RESULTS: In group A, no significant differences in rifapentine concentrations in the liver were detected between any two time points (P > 0.05). However, the differences in rifapentine concentrations between day 10 and day 21 were statistically significant (P < 0.05); for days 21, 35, 46, and 60, the differences in rifapentine concentrations between two sequential time points were not statistically significant (P > 0.05). In group B, the differences in rifapentine concentration between days 3 and 10 in vertebral bone and in paravertebral muscles were statistically significant (P < 0.05). Rifapentine was detected in the vertebral bone tissue in the group C animals. The rifapentine concentrations between two sequential time points were statistically significant (P < 0.05). Rifapentine could not be detected in the paravertebral muscles 46 days after the operation. The differences in rifapentine concentrations between two sequential time points among days 3, 10, 21, and 35 were statistically significant (P < 0.05). CONCLUSIONS: After paravertebral implantation of rifapentine polylactic acid sustained-release microspheres, the concentration of rifapentine in local vertebral bone tissues was maintained above the TB minimum inhibitory concentration for up to 60 days with no apparent accumulation of the drug in other tissues.