 Therapeutic drug monitoring TDM signifies individualised pharmacological dosing, based on the plasma levels that each patient presents. This strategy has been broadly used in the field of the treatment of other medical conditions and is acquiring growing interest in the field of antiretroviral treatment. Thus, the use of TDM for the treatment of naïve patients with nelfinavir or with indinavir has translated into an increase in the proportion of individuals with suppressed viral load and also into a reduction in HAART-induced adverse events . However, data on the utility of the therapeutic monitoring of the levels of efavirenz in HIV-infected patients are very scant. 