Urine colorimetry to detect Low rifampin exposure during tuberculosis therapy: a proof-of-concept study

Abstract

Background: The cost and complexity of current approaches to therapeutic drug monitoring during tuberculosis (TB) therapy limits widespread use in areas of greatest need. We sought to determine whether urine colorimetry could have a novel application as a form of therapeutic drug monitoring during anti-TB therapy.

Methods: Among healthy volunteers, we evaluated 3 dose sizes of rifampin (150 mg, 300 mg, and 600 mg), performed intensive pharmacokinetic sampling, and collected a timed urine void at 4 h post-dosing. The absorbance peak at 475 nm was measured after rifamycin extraction. The optimal cutoff was evaluated in a study of 39 HIV/TB patients undergoing TB treatment in Botswana.

Results: In the derivation study, a urine colorimetric assay value of 4.0 × 10(-2) Abs, using a timed void 4 h after dosing, demonstrated a sensitivity of 92 % and specificity of 60 % to detect a peak rifampin concentration (Cmax) under 8 mg/L, with an area under the ROC curve of 0.92. In the validation study, this cutoff was specific (100 %) but insensitive (28 %). We observed similar test characteristics for a target Cmax target of 6.6 mg/L, and a target area under the drug concentration-versus-time curve (AUC0-8) target of 24.1 mg•hour/L.

Conclusions: The urine colorimetric assay was specific but insensitive to detect low rifampin serum concentrations among HIV/TB patients. In future work we will attempt to optimize sampling times and assay performance, with the goal of delivering a method that can translate into a point-of-care assessment of rifampin exposure during anti-TB therapy.

Keywords: Point-of-care; Therapeutic drug monitoring; Tuberculosis.

Fig. 1

Calibration curve for the urine colorimetric assay

Fig. 2

Correlation between urine colorimetric assay and serum rifampin C_max among healthy volunteers

Fig. 3

ROC analysis for urine colorimetric assay to detect rifampin C_max less than 8 mg/L

Fig. 4

Individual rifampin serum concentration versus time among HIV/TB patients in the validation cohort

Fig. 5

Distribution of urine colorimetric assay among HIV/TB patients based on a serum rifampin target attainment of (a) C _max 8mg/L, (b) C _max 6.6mg/L, and (c) AUC_0-8 24.1mg^*hr/L

Fig. 6

ROC analysis for urine colorimetric assay to detect rifampin C_max less than 8 mg/L among HIV/TB patients

Fig. 7

ROC analysis for urine colorimetric assay to detect rifampin C_max less than 6.6 mg/L among HIV/TB patients

Fig. 8

ROC analysis for urine colorimetric assay to detect rifampin AUC_0–8 less than 24.1 mg•hour/L among HIV/TB patients