title: Therapeutic drug monitoring of A77 1726, the active metabolite of leflunomide: serum concentrations predict response to treatment in patients with rheumatoid arthritis.
abstract: BACKGROUND
  Leflunomide is the prodrug of the disease modifying antirheumatic metabolite A77 1726. More than 50% of patients withdraw from leflunomide treatment within one year, mainly because of adverse drug reactions. Therapeutic drug monitoring of A77 1726 may be useful in predicting the efficacy of leflunomide treatment.
  
  
  OBJECTIVE
  To study the relation between A77 1726 steady state serum concentrations and disease activity using the 28 joint (DAS28) response.
  
  
  METHODS
  Outpatients with rheumatoid arthritis on a stable leflunomide dose for >4 months were included. DAS28 score and adverse drug reactions were recorded. Blood samples were taken for determination of A77 1726 concentrations. The primary end point was the relation of serum A77 1726 concentrations with DAS28 response category.
  
  
  RESULTS
  Serum A77 1726 concentrations were determined in 52 patients. A receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 0.73 (95% confidence interval, 0.54 to 0.93) (p<0.05). The sensitivity exceeded 99% at concentrations below 16 mg/l. DAS28 values at the point of sampling showed no relation with A77 1726 concentrations (AUC of the ROC curve = 0.50 (0.33 to 0.67) (NS)).
  
  
  CONCLUSIONS
  A77 1726 steady state serum concentrations show a relation with DAS28 response. Determination of serum A77 1726 concentrations in patients with insufficient response to treatment may help when decisions have to be made about continuation of treatment or dose adjustment.
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, Medisch Centrum Leeuwarden, 8901 BR Leeuwarden, Netherlands. e.n.van.roon@znb.nl
authors.forename: E N
authors.initials: EN
authors.lastname: van Roon
authors.forename: T L T A
authors.initials: TL
authors.lastname: Jansen
authors.forename: M A F J
authors.initials: MA
authors.lastname: van de Laar
authors.forename: M
authors.initials: M
authors.lastname: Janssen
authors.forename: J P
authors.initials: JP
authors.lastname: Yska
authors.forename: R
authors.initials: R
authors.lastname: Keuper
authors.forename: P M
authors.initials: PM
authors.lastname: Houtman
authors.forename: J R B J
authors.initials: JR
authors.lastname: Brouwers
mesh_terms: D000368:Aged; D000814:Aniline Compounds / Q000097:blood* / Q000627:therapeutic use; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000097:blood* / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000188:drug therapy*; D003437:Crotonates; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D006801:Humans; D006885:Hydroxybutyrates / Q000097:blood* / Q000627:therapeutic use; D007555:Isoxazoles / Q000627:therapeutic use*; D000077339:Leflunomide; D008297:Male; D008875:Middle Aged; D009570:Nitriles; D011355:Prodrugs / Q000627:therapeutic use; D012372:ROC Curve; D012720:Severity of Illness Index; D014052:Toluidines; D016896:Treatment Outcome
chemical_list: D000814:Aniline Compounds; D000894:Anti-Inflammatory Agents, Non-Steroidal; D003437:Crotonates; D006885:Hydroxybutyrates; D007555:Isoxazoles; D009570:Nitriles; D011355:Prodrugs; D014052:Toluidines; C527525:teriflunomide; D000077339:Leflunomide