Evaluation of dried blood spot sampling for pharmacokinetic research and therapeutic drug monitoring of anti-tuberculosis drugs in children.

Background: Dried blood spot (DBS) sampling for pharmacokinetic (PK) studies and therapeutic drug monitoring have unique advantages over venous sampling. This study aimed to evaluate a DBS method for first-line anti-tuberculosis drugs in children, and DBS sampling to assess PK parameters.
Methods: Paraguayan children were treated according to the revised paediatric dosing scheme of the World Health Organization. A PK curve was performed both with DBS sampling and conventional venous sampling for rifampicin, pyrazinamide and ethambutol. Passing-Bablok regression, Bland-Altman plots and predictive performance evaluation were used to assess agreement between DBS and plasma concentrations. The percentages of patients attaining population PK values for C _max and AUC _0-24h were calculated.
Results: After use of a conversion factor, Passing-Bablok regression showed no significant proportional or systematic bias between DBS and plasma concentrations. Bland-Altman plots showed that 95% of the ratios of the DBS predicted:observed plasma concentrations lay between 0.6 and 1.4 for rifampicin, 0.5 and 1.6 for pyrazinamide and -0.4 and 2.8 for ethambutol. DBS measurements showed acceptable predictive performance for rifampicin and pyrazinamide, but not for ethambutol. Assessment of C _max target attainment was 62.5% for isoniazid, 25% for rifampicin, 100% for pyrazinamide and 75% for ethambutol.
Conclusion: For rifampicin and pyrazinamide, the DBS method was accurate in predicting plasma concentrations, and was used successfully for PK parameter assessment. However, predicting ethambutol plasma concentrations with DBS measurement was associated with too much imprecision. Despite higher dosing, only 25% of the population reached average target adult rifampicin exposures.
(Copyright © 2018. Published by Elsevier B.V.)