Therapeutic Drug Monitoring Study of Reduced-Dose Efavirenz (400 mg) in Combo Tablet for Patients Receiving Atripla With Viral Suppression in Taiwan

Inclusion Criteria: * Patients who are receiving co-formulated TDF/ FTC/ EFV (600 mg) and have achieved an undetectable plasma viral load (\<50 copies/mL) for 6 months or longer at screening visit. * Having C12 EFV of 1 mg/L or greater at screening. * (C12 EFV will be determined by using blood sample collected 12 ± 1 hour after previous dosing of co-formulated TDF/ FTC/ EFV (600 mg). * No known treatment failure to regimens containing TDF, 3TC or FTC, plus EFV. * Infected with HIV harboring no known resistance-associated mutations to EFV, TDF, 3TC or FTC. * No known allergies to EFV, TDF, 3TC or FTC. * Aged ≧20 years. * Calculated creatinine clearance (ClCr) ≥ 50 mL/min (Cockcroft-Gault formula). * Provision of written informed consent. Exclusion Criteria: * The following laboratory values: * Absolute neutrophil count (ANC) \<500 cells/μL * Hemoglobin \<7.0 g/dL * Platelet count \<50,000 cells/μL * Serum alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST) levels \>5x upper limit of normal (ULN) * Pregnant women or nursing mothers. * Active opportunistic or malignant disease not under adequate control. * Use of immunomodulators within 30 days prior to screening visit. * Use any of the prohibited medications: bepridil, astemizole, terfenadine, dihydroergotamine, ergometrine, ergotamine, systemic cytotoxic chemotherapy, amodiaquine, pimozide, midazolam, triazolam, cisapride、St John's Wort、 Elbasvir/Grazoprevir and Simeprevir.