Pharmacokinetics and dose response of anti-TB drugs in rat infection model of tuberculosis

• Published in: Tuberculosis (Edinburgh, Scotland) Scotland), 2014-05, Vol.94 (3), p.282-286
• Main Authors: Kumar, Naveen, Vishwas, K.G, Kumar, Mahesh, Reddy, Jitendar, Parab, Manish, Manikanth, C.L, Pavithra, B.S, Shandil, R.K
• Format: Article
• Language: English
• Subjects: Animals; Antitubercular Agents - administration & dosage; Antitubercular Agents - pharmacokinetics; Bacterial Load - drug effects; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Infectious Disease; Male; Mycobacterium tuberculosis; Pulmonary/Respiratory; Rats, Wistar; Treatment Outcome; Tuberculosis, Pulmonary - drug therapy
• ISSN: 1472-9792; 1873-281X
• DOI: 10.1016/j.tube.2014.02.004

Summary Robust and physiologically relevant infection models are required to investigate pharmacokinetic–pharmacodynamic (PK/PD) correlations for anti-tuberculosis agents at preclinical discovery. We have validated an inhalation-based rat infection model of tuberculosis harbouring mycobacteria in a replicating state, that is suitable for investigating pharmacokinetics and drug action of anti-tubercular agents. A reproducible and actively replicating lung infection was established in Wistar rats by inhalation of a series of graded inocula of Mycobacterium tuberculosis . Following an initial instillation of ∼105  log10  CFU/lung, M. tuberculosis grew logarithmically for the first 3 weeks, and then entered into a chronic phase with no net increase in pulmonary bacterial loads. Dose response of front-line anti-TB drugs was investigated following pharmacokinetic measurements in the plasma of infected rats. Rifampicin, Isoniazid, and Ethambutol dosed per orally exhibited bactericidality and good dose response with maximal effect of 5.66, 4.66, and 4.80 log10  CFU reductions in the lungs, respectively. In contrast, Pyrazinamide was merely bacteriostatic with 1.92 log10  CFU/lung reduction and did not reduce the bacterial burden beyond the initial bacterial loads present at beginning of treatment in spite of high Pyrazinamide blood levels. Rat infection model with actively replicating bacilli provides a physiologically distinct and pharmacologically relevant model that can be exploited to distinguish investigational compounds in to bacteriostatic or bactericidal scaffolds. We propose that this rat infection model though need more drug substance, can be used in early discovery settings to investigate pharmacology of novel anti-tubercular agents for the treatment of active pulmonary tuberculosis.