title: Evaluation of an immunoassay for determination of plasma efavirenz concentrations in resource-limited settings.
abstract: BACKGROUND
  Therapeutic drug monitoring (TDM) may improve antiretroviral efficacy through adjustment of individual drug administration. This could result in reduced toxicity, prevent drug resistance, and aid management of drug-drug interactions. However, most measurement methods are too costly to be implemented in resource-limited settings. This study evaluated a commercially available immunoassay for measurement of plasma efavirenz.
  
  
  METHODS
  The immunoassay-based method was applied to measure efavirenz using a readily available Humastar 80 chemistry analyzer. We compared plasma efavirenz concentrations measured by the immunoassay with liquid chromatography tandem mass spectrometry (LC-MS/MS) (reference method) in 315 plasma samples collected from HIV patients on treatment. Concentrations were categorized as suboptimal<1 µg/ml, normal 1-4 µg/ml or high>4 µg/ml. Agreement between results of the methods was assessed via Bland-Altman plot and κ statistic values.
  
  
  RESULTS
  The median Interquartile range (IQR) efavirenz concentration was 2.8 (1.9; 4.5) µg/ml measured by the LC-MS/MS method and 2.5 (1.8; 3.9) µg/ml by the immunoassay and the results were well correlated (ρ=0.94). The limits of agreement assessed by Bland-Altman plots were -2.54; 1.70 µg/ml. Although immunoassay underestimated high concentrations, it had good agreement for classification into low, normal or high concentrations (K=0.74).
  
  
  CONCLUSIONS
  The immunoassay is a feasible alternative to determine efavirenz in areas with limited resources. The assay provides a reasonable approximation of efavirenz concentration in the majority of samples with a tendency to underestimate high concentrations. Agreement between tests evaluated in this study was clinically satisfactory for identification of low, normal and high efavirenz concentrations.
authors.affiliation: Department of Medical Laboratory Sciences & Pathology, Jimma University, Jimma, Ethiopia; Department of Infectious Diseases, Odense University Hospital, Odense, Denmark; alemseged.abdisssa@ju.edu.et.
authors.forename: Alemseged
authors.initials: A
authors.lastname: Abdissa
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine and Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Lubbe
authors.initials: L
authors.lastname: Wiesner
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine and Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Helen
authors.initials: H
authors.lastname: McIlleron
authors.affiliation: Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Friis
authors.affiliation: Department of Infectious Diseases, Odense University Hospital, Odense, Denmark.
authors.forename: Ase Bengård
authors.initials: AB
authors.lastname: Andersen
authors.affiliation: Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Pernille
authors.initials: P
authors.lastname: Kaestel
mesh_terms: D000480:Alkynes; D019380:Anti-HIV Agents / Q000097:blood*; D048588:Benzoxazines / Q000097:blood*; D002853:Chromatography, Liquid / Q000379:methods; D003521:Cyclopropanes; D015658:HIV Infections / Q000097:blood / Q000188:drug therapy; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods* / Q000592:standards; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D000480:Alkynes; D019380:Anti-HIV Agents; D048588:Benzoxazines; D003521:Cyclopropanes; C098320:efavirenz
keywords: LC–MS/MS; TDM; antiretroviral therapy; efavirenz; immunoassay; method evaluation