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

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