title: Low blood concentration of hydroxychloroquine is a marker for and predictor of disease exacerbations in patients with systemic lupus erythematosus.
abstract: OBJECTIVE
  To study the possible relationship between whole-blood hydroxychloroquine (HCQ) concentrations and clinical efficacy of HCQ in patients with systemic lupus erythematosus (SLE).
  
  
  METHODS
  Whole-blood HCQ concentrations were measured, under blinded conditions, in 143 unselected patients with SLE who had been receiving HCQ 400 mg daily for at least 6 months. The relationship of these concentrations to current disease activity and to subsequent exacerbations during 6 months of followup was investigated.
  
  
  RESULTS
  At baseline, 23 patients had active disease (mean +/- SD SLE Disease Activity Index 12.4 +/- 7.5). The mean whole-blood HCQ concentration in this group was significantly lower than that in the 120 patients with inactive disease (694 +/- 448 ng/ml versus 1,079 +/- 526 ng/ml; P = 0.001). Among the 120 patients who had inactive disease at baseline, the mean HCQ concentration at baseline in the 14 (12%) who had disease exacerbations during followup was significantly lower than that in the patients whose disease remained inactive. Multivariate logistic regression showed that the HCQ concentration was the only predictor of exacerbation (odds ratio 0.4 [95% confidence interval 0.18-0.85], P = 0.01). Receiver operating characteristic curve analysis showed that a whole-blood HCQ concentration cutoff of 1,000 ng/ml had a negative predictive value of 96% for exacerbation during followup.
  
  
  CONCLUSIONS
  Low whole-blood HCQ concentrations are associated with SLE disease activity and are a strong predictor of disease exacerbation. Regular drug assaying and individual tailoring of treatment might help to improve the efficacy of HCQ treatment in patients with SLE.
authors.affiliation: Assistance Publique-Hôpitaux de Paris, Centre Hospitalier Universitaire Pitié-Salpêtrière, Université Paris VI Pierre et Marie Curie, Paris, France. nathalie.costedoat@psl.aphp.fr
authors.forename: Nathalie
authors.initials: N
authors.lastname: Costedoat-Chalumeau
authors.forename: Zahir
authors.initials: Z
authors.lastname: Amoura
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Hulot
authors.forename: Hala Abou
authors.initials: HA
authors.lastname: Hammoud
authors.forename: Guy
authors.initials: G
authors.lastname: Aymard
authors.forename: Patrice
authors.initials: P
authors.lastname: Cacoub
authors.forename: Camille
authors.initials: C
authors.lastname: Francès
authors.forename: Bertrand
authors.initials: B
authors.lastname: Wechsler
authors.forename: Du Le Thi
authors.initials: du LT
authors.lastname: Huong
authors.forename: Pascale
authors.initials: P
authors.lastname: Ghillani
authors.forename: Lucile
authors.initials: L
authors.lastname: Musset
authors.forename: Philippe
authors.initials: P
authors.lastname: Lechat
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Piette
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D018450:Disease Progression; D005260:Female; D006801:Humans; D006886:Hydroxychloroquine / Q000097:blood* / Q000627:therapeutic use; D016015:Logistic Models; D008137:Longitudinal Studies; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012720:Severity of Illness Index
chemical_list: D015415:Biomarkers; D006886:Hydroxychloroquine