Therapeutic drug monitoring is a process that allows clinicians to quantitate and control drug therapy. Serum concentration data allow for the explicit determination of pharmacokinetic and pharmacodynamic parameters for individual patients. This information assists the clinician in designing treatment regimens that produce a therapeutic response while minimizing avoidable toxicity. In particular, patients with clinically advanced mycobacterial infections, those with infections caused by strains of M. tuberculosis with acquired drug resistance, or species of nontuberculosis which are inherently drug-resistant, and those with co-morbid conditions such as AIDS may benefit from this process.