Therapeutic drug monitoring is usually not performed in a patient being treated for tuberculosis but should be considered if certain conditions are present.
When to consider therapeutic drug monitoring during antituberculous therapy:
(1) slow to respond (failure to respond) to standard antituberculous therapy
(2) noncompliance suspected (may not be an issue in directly-observed therapy, DOT)
(3) possible drug-resistant M. tuberculosis
(4) malabsorption
(5) possible drug interaction increasing clearance
(6) HIV-positivity
(7) end-stage liver and/or renal disease
(8) symptoms suspected to be dose-related adverse effects
Criteria of Mehta et al for being a slow responder to therapy:
(1) sputum and cultures remain positive for M. tuberculosis after 3 months of therapy
(2) patient has not improved clinically after 3 months of therapy
(3) chest X-rays have not improved after 3 months of therapy
Testing that may be relevant in troubleshooting a patient:
(1) susceptibility testing of M. tuberculosis isolate
(2) molecular testing for resistance genes
(3) serum levels of antituberculous drugs at peak and/or trough
