In this issue of CHEST (see page 1770), Li and colleagues describe their experience using therapeutic drug monitoring (TDM) in the management of patients with multidrug-resistant (MDR) tuberculosis (TB). The authors are to be commended for quantifying their experience.
In clinical settings, and especially in outpatient clinic settings, there are a number of logistical difficulties related to TDM to overcome. In the experience of Li et al, only 45% of the patients who were considered to be candidates for TDM actually had samples collected, and the likely reasons for this were cited in their article. Patients who had been treated longer or who had more extensive disease appeared more likely to have TDM. Blood samples were not always collected at the desired times, making the interpretation more challenging, and for some of these cases, unfamiliarity with the procedures likely played a role. Finally, when presented with concentrations that were out of range, not all physicians chose to adjust the doses. This was understandable for cases in which the patients already were tolerating the drugs poorly or for cases in which therapy with the drugs was about to be discontinued. For other cases, physicians may have been reluctant to exceed “maximum” doses, as listed in TB treatment guidelines.