Urine Colorimetry for Tuberculosis Pharmacokinetics Evaluation in Children and Adults

TB remains a leading infectious disease cause-of-death worldwide, with an estimated 1.5 million TB deaths each year. There is wide variability in absorption and metabolism of the anti-TB drugs, and low drug concentrations in blood are associated with inferior TB treatment outcomes, including treatment failure, relapse, and the emergence of drug-resistant infections. According to the most recent CDC/ATS/IDSA guidelines for TB treatment, therapeutic drug monitoring should be routinely considered for use among patients in high-risk groups, including adults with co-morbid type 2 diabetes mellitus (DM) and children. However, therapeutic drug monitoring requires sophisticated laboratory techniques unavailable for millions of patients receiving TB therapy in resource-limited settings where the vast majority of TB cases are treated. A new approach to measuring anti-TB drug exposures, based on technology easily adapted to resource-limited settings, is vitally needed and would be in line the World Health Organization's goal of the optimization of anti-TB drug regimens as a key component of the End TB Strategy.

A simple, inexpensive test to identify pediatric and adult TB patients with low drug exposures, available at the point-of-care at the time of the patient encounter, would support clinical decision-making. The performance of therapeutic drug monitoring requires specialty laboratory capabilities, such as high-performance liquid chromatography or gas chromatography. Technical expertise is also required to collect, process, and ship samples to the specialty laboratory. In many high-burden settings, the complexity and cost of these laboratory methods preclude the use of therapeutic drug monitoring in the clinical care of tuberculosis patients. These complexities also foster a dependence of TB endemic sites on laboratories in resource-rich environments. Consequently, patients with inadequate drug exposures cannot be identified early in anti-TB therapy, at the critical time when dosing adjustments could be expected to improve treatment outcomes.

Urine colorimetry provides a low-technology approach for measuring anti-TB drug exposures, suitable for point-of-care testing. Colorimetry is the measurement of intensity of signal at a specific wavelength in the visible region of the spectrum. Urine colorimetry was evaluated as a method to assess the relative bioavailability of different fixed-dose combinations of anti-TB drugs administered to healthy volunteers. The study is based on the scientific premise that more detailed anti-TB drug exposure information can be obtained from urine sampling during TB treatment, not only to determine the presence or absence of drugs or metabolites, but to determine whether the presence of drugs or metabolites has surpassed a critical exposure threshold, informing drug dosing decision-making at the point-of-care. Potential advantages of urine colorimetric methods include a non-invasive sampling approach, improved patient acceptability, and the low cost and stability of chemical reagents. Colorimetry is particularly suited for point-of-care diagnostics, possibly with battery-operated or smartphone-based tools. With a simple diagnostic test available at the point-of-care, with results provided at the time of the clinical encounter, the TB clinician will be able to adjust drug doses and optimize regimens.