Pharmacokinetics of anti-TB drugs in children and adolescents with drug-resistant TB: a multicentre observational study from India.

BACKGROUND: Drug-resistant tuberculosis (DR-TB) is one of the challenging forms of TB to treat, not only in adults but also in children and adolescents. Further, there is a void in the treatment strategy exclusively for children due to various reasons, including paucity of pharmacokinetic (PK) data on anti-TB drugs across the globe. In this context, the present study aimed at assessing the PK of some of the anti-TB drugs used in DR-TB treatment regimens. METHOD: A multicentre observational study was conducted among DR-TB children and adolescents (n = 200) aged 1-18 years (median: 12 years; IQR: 9-14) treated under programmatic settings in India. Steady-state PK (intensive: n = 89; and sparse: n = 111) evaluation of moxifloxacin, levofloxacin, cycloserine, ethionamide, rifampicin, isoniazid and pyrazinamide was carried out by measuring plasma levels using HPLC methods. RESULTS: In the study population, the frequency of achieving peak plasma concentrations ranged between 13% (for rifampicin) to 82% (for pyrazinamide), whereas the frequency of suboptimal peak concentration for pyrazinamide, cycloserine, moxifloxacin, levofloxacin and rifampicin was 15%, 19%, 29%, 41% and 74%, respectively. Further, the frequency of supratherapeutic levels among patients varied between 3% for pyrazinamide and 60% for isoniazid. In the below-12 years age category, the median plasma maximum concentration and 12 h exposure of moxifloxacin were significantly lower than that of the above-12 years category despite similar weight-adjusted dosing. CONCLUSIONS: Age significantly impacted the plasma concentration and exposure of moxifloxacin. The observed frequencies of suboptimal and supratherapeutic concentrations underscore the necessity for dose optimization and therapeutic drug monitoring in children and adolescents undergoing DR-TB treatment.

Development and Validation of a Simple High-Pressure Liquid Chromatography-Ultraviolet Detection Method for Simultaneous Quantitation of First-Line Anti-Tuberculosis Drugs in Formulations of Fixed-Dose Combination.

The current treatment protocol for drug-sensitive tuberculosis involves all four first-line anti-tuberculosis drugs: rifampicin, isoniazid, pyrazinamide and ethambutol hydrochloride in a single tablet, known as fixed-dose combination tablets. However, the analytical methods are scanty to test all these drugs simultaneously in a single run without any pre-sample process or using a simple method suitable for resource-limited settings. In this method, 50 mM potassium phosphate buffer containing 0.2% triethylamine (without pH adjustment) added with acetonitrile (98:2, v/v) was served as mobile phase A, while mobile phase B was 100% acetonitrile. All four drugs were separated within 10.3 min using a gradient mobile phase program in a C18 column (150 mm × 4.6 mm; 5 µm) and detected at two ultraviolet wavelengths (238 nm for rifampicin, isoniazid and pyrazinamide, and 210 nm for ethambutol hydrochloride). The method was selective, sensitive and linear with a correlation coefficient >0.999 with the acceptable precision and accuracy (<2% relative standard deviation) for all four drugs. In conclusion, the method is simple and it does not require any pH adjustment of the buffer/mobile phase, and within 11 min, the separation of all four drugs can be achieved. Overall, the method is suitable for quality testing of fixed-dose combination tablets in limited-resource settings.

Long-Term Intake of Linezolid Elevates Drug Exposure and Reduces Drug Clearance and Elimination in Adults With Drug-Resistant Pulmonary Tuberculosis.

PURPOSE: Pharmacokinetic (PK) studies are critical for dose optimization, and there is a paucity of linezolid (LZD) PK data for prolonged use in drug-resistant tuberculosis (DR-TB). Therefore, the authors evaluated the pharmacokinetics of LZD at two-time intervals in DR-TB during long-term use. METHODS: PK evaluation of LZD was performed at the end of the 8th and 16th weeks of treatment in a randomly selected subset of adult pre-extensively drug-resistant pulmonary tuberculosis patients (n = 18) from a multicentric interventional study (Building Evidence to Advance Treatment of TB/BEAT study; CTRI/2019/01/017310), wherein a daily dose of 600 mg LZD was used for 24 weeks. Plasma LZD levels were measured using a validated high-pressure liquid chromatography (HPLC) method. RESULTS: The LZD median plasma C max was comparable between the 8th and 16th weeks [18.3 mg/L, interquartile range (IQR: 15.5-20.8 and 18.8 mg/L, IQR: 16.0-22.7, respectively)]. However, the trough concentration increased significantly in the 16th week (3.16 mg/L, IQR: 2.30-4.76), compared with the 8th week (1.98 mg/L, IQR: 0.93-2.75). Furthermore, compared with the 8th week, in the 16th week, there was a significant increase in drug exposure (AUC 0-24 = 184.2 mg*h/L, IQR: 156.4-215.8 versus 233.2 mg*h/L, IQR: 187.9-277.2), which corroborated with a longer elimination half-life (6.94 hours, IQR: 5.55-7.99 versus 8.47 hours, IQR:7.36-11.35) and decreased clearance (2.91 L/h, IQR: 2.45-3.33 versus 2.19 L/h, IQR: 1.49-2.78). CONCLUSIONS: Long-term daily intake of 600 mg LZD resulted in a significant elevation in trough concentration (>2.0 mg/L) in 83% of the study participants. Furthermore, increased LZD drug exposure may be partly because of decreased clearance and elimination. Overall, the PK data underscore the need for dose adjustment when LZDs are intended for long-term treatment.