Efavirenz, a nonnucleoside
reverse transcriptase inhibitor, is a highly effective and widely prescribed
antiretroviral agent. It is recommended as first-line treatment of human immunodeficiency virus (
HIV) infection. The standard dose of
efavirenz is 600 mg/day; however, adverse central nervous system effects limit its use. Few data citing use of
efavirenz at lower doses have been published. We describe a 35-year-old man with
HIV infection whose virologic suppression was maintained after 18 months of treatment with
efavirenz 400 mg/day. Genetic testing for
cytochrome P450 (CYP) 2B6 showed that the patient was a heterozygous variant; patients with this polymorphism tend to have higher plasma
efavirenz concentrations and slower plasma
efavirenz clearance (prolonged elimination half-lives). Therapeutic
drug monitoring also supported the
dose reduction in this patient. Even with the 400-mg dose, the patient's plasma trough concentrations exceeded the upper limit of the therapeutic range. However, as he remained completely asymptomatic with this dose, no further
dose reduction was necessary. This case report provides evidence that reduced
efavirenz doses may be effective in the treatment of
HIV infection. In addition, this case demonstrates that pharmacogenetic and pharmacokinetic testing combined with therapeutic
drug monitoring may be used to guide reduced-dose,
efavirenz-based
therapy.