title: Patient case: impact of smoking cessation on international normalized ratio.
abstract: BACKGROUND
  The concurrent use of cigarettes while on warfarin therapy is a common occurrence. Smoking cessation among patients on chronic warfarin therapy is suspected to reduce drug clearance that may require dose adjustments. This type of interaction is particularly important when dealing with narrow therapeutic medications, as is the case with warfarin. Our case describes a series of supratherapeutic international normalized ratios (INRs) due to smoking cessation while on concomitant warfarin therapy. Patient Case: A 51-year-old male presented to the anticoagulation clinic for management of his warfarin therapy for an acute deep vein thrombosis. After 2 months of stable, therapeutic INR levels, the patient abruptly decreased his smoking from 1 pack/day to one-half pack/day and then subsequently stopped smoking completely. The patient's smoking cessation resulted in a major modification of his required weekly warfarin dose to maintain a therapeutic INR (a 39% dose reduction).
  
  
  CONCLUSIONS
  This case exemplifies how certain lifestyle factors, such as smoking, can alter the pharmacokinetics of patients on chronic warfarin therapy. This is the first case to demonstrate a greater than 30% reduction in the weekly warfarin dose following smoking cessation.
authors.affiliation: Tampa General Hospital, Department of Pharmacy Services, Tampa, FL, USA shanejordan003@aol.com.
authors.forename: Shane D
authors.initials: SD
authors.lastname: Jordan
authors.affiliation: Bayfront Health, St. Petersburg, FL, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Stone
authors.affiliation: Tampa General Hospital, Department of Pharmacy Services, Tampa, FL, USA.
authors.forename: Earnest
authors.initials: E
authors.lastname: Alexander
authors.affiliation: Tampa General Hospital, Department of Pharmacy Services, Tampa, FL, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Haley
authors.affiliation: Tampa General Hospital, Department of Pharmacy Services, Tampa, FL, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: McKee
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D012907:Smoking / Q000378:metabolism*; D016540:Smoking Cessation; D020246:Venous Thrombosis / Q000188:drug therapy; D014859:Warfarin / Q000008:administration & dosage* / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D014859:Warfarin
keywords: international normalized ratio; smoking cessation; warfarin