title: Recent caffeine ingestion reduces adenosine efficacy in the treatment of paroxysmal supraventricular tachycardia.
abstract: OBJECTIVE
  Caffeine, an adenosine receptor blocker, should theoretically reduce adenosine efficacy in the treatment of paroxysmal supraventricular tachycardia (SVT). We aimed to determine the effect of recent caffeine ingestion on the likelihood of reversion of SVT with adenosine.
  
  
  METHODS
  This was a multicenter, case-control study of adult patients with SVT treated with adenosine between September 2007 and July 2008. The primary endpoint was reversion to sinus rhythm (SR) after a 6-mg adenosine bolus, as a function of recent (within 2, 4, 6, and 8 hours) caffeine ingestion. Caffeine ingestion data were collected using a self-administered questionnaire.
  
  
  RESULTS
  Of 68 patients enrolled, 52 (76.5%, 95% confidence interval [CI] = 64.4% to 85.6%) reverted after a 6-mg adenosine bolus. There were no significant differences in age, sex, or daily caffeine ingestion between patients who did and did not revert (p > 0.05). However, as a group, patients who did not revert had recently ingested significantly more caffeine (p < 0.05). If caffeine had been ingested less than 2 or 4 hours before the adenosine bolus, the odds of reversion to SR were significantly reduced (odds ratio [OR] = 0.18, 95% CI = 0.04 to 0.93; and OR = 0.14, 95% CI = 0.04 to 0.49, respectively). If caffeine had been ingested less than 6 or 8 hours before the adenosine, the odds of reversion were not reduced (OR = 0.31, 95% CI = 0.09 to 1.02; and OR = 0.31, 95% CI = 0.09 to 1.08, respectively).
  
  
  CONCLUSIONS
  Ingestion of caffeine less than 4 hours before a 6-mg adenosine bolus significantly reduces its effectiveness in the treatment of SVT. An increased initial adenosine dose may be indicated for these patients.
authors.affiliation: University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Miguel S
authors.initials: MS
authors.lastname: Cabalag
authors.forename: David McDonald
authors.initials: DM
authors.lastname: Taylor
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Knott
authors.forename: Paul
authors.initials: P
authors.lastname: Buntine
authors.forename: DeVilliers
authors.initials: D
authors.lastname: Smit
authors.forename: Alastair
authors.initials: A
authors.lastname: Meyer
mesh_terms: D000241:Adenosine / Q000008:administration & dosage* / Q000592:standards; D000368:Aged; D000369:Aged, 80 and over; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage* / Q000592:standards; D002110:Caffeine / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011795:Surveys and Questionnaires; D013617:Tachycardia, Supraventricular / Q000188:drug therapy*; D013997:Time Factors
chemical_list: D000889:Anti-Arrhythmia Agents; D002110:Caffeine; D000241:Adenosine