Importance of Therapeutic Drug Monitoring of Rifampicin.

Therapeutic Drug Monitoring (TDM) is a routinely practised clinical laboratory technique which aids the clinicians with a clear clinical judgement of the drug therapy and optimize the doses if necessary. Rifampicin is the most important and potent component of first line therapy of tuberculosis (TB). Several factors like age, weight, gender, doses and formulations, gastro-intestinal disorders, ethnicity etc alter the absorption and bioavailability of rifampicin thus altering the drug levels. Low plasma levels of rifampicin may play a plausible role in slow response to therapy, treatment failure or relapse or acquired drug resistance. TB Patients with further complicated conditions like diabetes or HIV are at an increased risk for poor drug absorption and drug-drug interactions. A standard treatment regimen may be inadequate for some cases as the clinical status of patients vary from case to case. TDM can be used as a clinical tool for identifying patients at high risk of treatment failure, delayed response, drug-drug interactions and help optimization of therapy. In the past two decades numerous reports of TDM of anti-tuberculosis drugs have been reported wherein low rifampicin levels have been a major concern. Rifampicin exhibit concentration dependent killing of mycobacteria. A 2 hour post-dose sample approximates the peak plasma rifampicin concentration (Cmax) and is recommended for TDM of rifampicin. An additional 6 hour sample may be collected to distinguish between delayed absorption and malabsorption. Combined with clinical and bacteriological data, TDM can help clinicians treat slow response / complicated TB patients.