title: Hydroxychloroquine Blood Levels in Systemic Lupus Erythematosus: Clarifying Dosing Controversies and Improving Adherence.
abstract: OBJECTIVE
  Hydroxychloroquine (HCQ) is used for its effect on systemic lupus erythematosus (SLE) disease activity and longterm benefits. This can be limited by adherence. One way to assess adherence is to measure blood levels. Conflicting data exist regarding blood levels and disease activity. There is disagreement about dosing; rheumatologists recommend weight-based dosing while some other specialists advocate height-based "ideal body weight" dosing.
  
  
  METHODS
  Patients were prescribed HCQ not exceeding 6.5 mg/kg (max 400 mg/day). In hemodialysis, the dose was 200 mg after each session, and in renal insufficiency it was 200 mg/day. Levels were measured at each visit with a therapeutic range of 500-2000 ng/ml. Patients were divided according to baseline blood level. To assess the effect of measurement and counseling on adherence, we compared the proportion of patients with a level of 500 ng/ml or higher based on the number of prior assessments.
  
  
  RESULTS
  The proportion of patients with HCQ levels in the therapeutic range differed significantly by age, sex, and Vitamin D level. There was a trend toward lower levels with renal failure. Blood levels were similar regardless of height and ideal body weight. Comparing those with undetectable, subtherapeutic, and therapeutic levels, disease activity decreased (SLE Disease Activity Index 2.92, 2.36, and 2.20, p = 0.04 for trend). At first, 56% were therapeutic, and by the third measurement this increased to 80% (p ≤ 0.0001).
  
  
  CONCLUSIONS
  There was a trend toward higher disease activity with lower HCQ levels. Renal failure dosing led to suboptimum levels. We show that weight-based dosing (max 400 mg daily) is appropriate and that height does not appear to influence levels. Measurement, counseling, and repeated testing can increase adherence rates.
authors.affiliation: From the Department of Rheumatology, Johns Hopkins University School of Medicine; Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital, Baltimore; Department of Epidemiology and Public Health, University of Maryland, College Park, Maryland, USA.L. Durcan, MD, Department of Rheumatology, Johns Hopkins University School of Medicine; W.A. Clarke, PhD, Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital; L.S. Magder, MPH, PhD, Department of Epidemiology and Public Health, University of Maryland; M. Petri, MD, MPH, Department of Rheumatology, Johns Hopkins University School of Medicine.
authors.forename: Laura
authors.initials: L
authors.lastname: Durcan
authors.affiliation: From the Department of Rheumatology, Johns Hopkins University School of Medicine; Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital, Baltimore; Department of Epidemiology and Public Health, University of Maryland, College Park, Maryland, USA.L. Durcan, MD, Department of Rheumatology, Johns Hopkins University School of Medicine; W.A. Clarke, PhD, Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital; L.S. Magder, MPH, PhD, Department of Epidemiology and Public Health, University of Maryland; M. Petri, MD, MPH, Department of Rheumatology, Johns Hopkins University School of Medicine.
authors.forename: William A
authors.initials: WA
authors.lastname: Clarke
authors.affiliation: From the Department of Rheumatology, Johns Hopkins University School of Medicine; Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital, Baltimore; Department of Epidemiology and Public Health, University of Maryland, College Park, Maryland, USA.L. Durcan, MD, Department of Rheumatology, Johns Hopkins University School of Medicine; W.A. Clarke, PhD, Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital; L.S. Magder, MPH, PhD, Department of Epidemiology and Public Health, University of Maryland; M. Petri, MD, MPH, Department of Rheumatology, Johns Hopkins University School of Medicine.
authors.forename: Laurence S
authors.initials: LS
authors.lastname: Magder
authors.affiliation: From the Department of Rheumatology, Johns Hopkins University School of Medicine; Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital, Baltimore; Department of Epidemiology and Public Health, University of Maryland, College Park, Maryland, USA.L. Durcan, MD, Department of Rheumatology, Johns Hopkins University School of Medicine; W.A. Clarke, PhD, Department of Pathology, Clinical Chemistry, Johns Hopkins University Hospital; L.S. Magder, MPH, PhD, Department of Epidemiology and Public Health, University of Maryland; M. Petri, MD, MPH, Department of Rheumatology, Johns Hopkins University School of Medicine.
authors.forename: Michelle
authors.initials: M
authors.lastname: Petri
mesh_terms: D000046:Academic Medical Centers; D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D015331:Cohort Studies; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006886:Hydroxychloroquine / Q000008:administration & dosage* / Q000097:blood*; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000175:diagnosis / Q000188:drug therapy*; D008297:Male; D020714:Maximum Tolerated Dose; D008875:Middle Aged; D011446:Prospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D012737:Sex Factors; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult; D016903:Drug Monitoring
chemical_list: D006886:Hydroxychloroquine
keywords: ADHERENCE; DISEASE ACTIVITY; HYDROXYCHLOROQUINE; SLE