title: Furosemide increases plasma oxypurinol without lowering serum urate--a complex drug interaction: implications for clinical practice.
abstract: OBJECTIVE
  To determine the effects of furosemide on serum urate (SU), plasma oxypurinol and urinary urate.
  
  
  METHODS
  Twenty-three cases with gout receiving furosemide and allopurinol were recruited. Twenty-three controls with gout receiving allopurinol but no diuretics were matched on age, gender, estimated glomerular filtration rate and allopurinol dose. SU, plasma oxypurinol and urinary urate were assessed on a single occasion. The effects of a single dose of furosemide 40 mg were examined in a separate group of 10 patients receiving allopurinol but not diuretic.
  
  
  RESULTS
  Cases had significantly higher SU and plasma oxypurinol compared with controls despite receiving similar doses of allopurinol. There was no difference in urinary urate excretion. There was a significant increase in area under the curve (AUC)(0-24) for oxypurinol after administration of furosemide 40 mg.
  
  
  CONCLUSIONS
  The interaction between allopurinol and furosemide results in increased SU and plasma oxypurinol. The exact mechanisms remain unclear but complex interactions that result in attenuation of the hypouricaemic effects of oxypurinol are likely.
  
  
  BACKGROUND
  Australian New Zealand Clinical Trials Registry, www.anzctr.org.au, 12609000529246.
authors.affiliation: Department of Medicine, University of Otago, Christchurch 8140, New Zealand. lisa.stamp@cdhb.govt.nz
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Stamp
authors.forename: Murray L
authors.initials: ML
authors.lastname: Barclay
authors.forename: John L
authors.initials: JL
authors.lastname: O'Donnell
authors.forename: Mei
authors.initials: M
authors.lastname: Zhang
authors.forename: Jill
authors.initials: J
authors.lastname: Drake
authors.forename: Christopher
authors.initials: C
authors.lastname: Frampton
authors.forename: Peter T
authors.initials: PT
authors.lastname: Chapman
mesh_terms: D000328:Adult; D000368:Aged; D000493:Allopurinol / Q000493:pharmacokinetics* / Q000627:therapeutic use; D019540:Area Under Curve; D016022:Case-Control Studies; D004232:Diuretics / Q000493:pharmacokinetics* / Q000627:therapeutic use; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D005260:Female; D005665:Furosemide / Q000493:pharmacokinetics* / Q000627:therapeutic use; D006073:Gout / Q000188:drug therapy* / Q000378:metabolism; D006074:Gout Suppressants / Q000493:pharmacokinetics* / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008875:Middle Aged; D010117:Oxypurinol / Q000097:blood*; D016896:Treatment Outcome; D014527:Uric Acid / Q000097:blood*; D014554:Urination / Q000187:drug effects
chemical_list: D004232:Diuretics; D006074:Gout Suppressants; D014527:Uric Acid; D000493:Allopurinol; D005665:Furosemide; D010117:Oxypurinol