title: Effect of grapefruit juice on cytochrome P450 2A6 and nicotine renal clearance.
abstract: OBJECTIVE
  Grapefruit juice is an inhibitor of the cytochrome P450 (CYP) 3A4 enzyme and transporters such as P-glycoprotein and organic anion transporting polypeptides, leading to clinically important interactions. Our objective was to study the effect of grapefruit juice on the pharmacokinetics of nicotine, which is primarily metabolized by the CYP2A6 enzyme.
  
  
  METHODS
  Ten volunteers were given a 2-mg oral dose of deuterium-labeled nicotine on 3 occasions together with 1 L of water, full-strength grapefruit juice, or half-strength grapefruit juice. Concentrations of nicotine and its metabolites were analyzed in plasma and urine for 8 hours.
  
  
  RESULTS
  Grapefruit juice inhibited the formation of cotinine from nicotine (area under the plasma cotinine concentration-time curve from 0 to 8 hours of 6807 min.ng/mL, 7805 min.ng/mL, and 8007 min.ng/mL for full-strength grapefruit juice, half-strength grapefruit juice, and water, respectively; repeated-measures ANOVA, P=.009). The time to peak plasma concentration of cotinine was delayed (216 minutes, 159 minutes, and 147 minutes, respectively; ANOVA, P=.011), and the peak plasma concentration was lower with grapefruit juice compared with water (18 ng/mL, 21 ng/mL, and 22 ng/mL, respectively; ANOVA, P=.010). Oral clearance, peak plasma concentration, and time to peak plasma concentration of nicotine were not affected. Grapefruit juice increased the renal clearance of nicotine (231 mL/min, 219 mL/min, and 123 mL/min, respectively; ANOVA, P=.045) and cotinine (19 mL/min, 14 mL/min, and 16 mL/min, respectively; ANOVA, P=.002).
  
  
  CONCLUSIONS
  Grapefruit juice inhibits the metabolism of nicotine to cotinine, a pathway mediated by CYP2A6, and increases the renal clearance of nicotine and cotinine. Nicotine oral clearance is not affected by grapefruit juice because the inhibition of hepatic metabolism is offset by the increase in the renal clearance of nicotine. However, other compounds metabolized by CYP2A6, as well as other drugs excreted via renal clearance mechanisms similar to those of nicotine, may be susceptible to significant pharmacokinetic grapefruit juice interactions.
authors.affiliation: Division of Clinical Pharmacology and Experimental Therapeutics, Medical Service, San Francisco General Hospital Medical Center, and Department of Medicine, University of California, San Francisco 94143-1220, USA.
authors.forename: Janne
authors.initials: J
authors.lastname: Hukkanen
authors.forename: Peyton
authors.initials: P
authors.lastname: Jacob
authors.forename: Neal L
authors.initials: NL
authors.lastname: Benowitz
mesh_terms: D000284:Administration, Oral; D000328:Adult; D019540:Area Under Curve; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001628:Beverages; D032083:Citrus paradisi; D003367:Cotinine / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism / Q000652:urine; D065637:Cytochrome P-450 CYP2A6; D003903:Deuterium; D005260:Female; D005731:Ganglionic Stimulants / Q000008:administration & dosage / Q000493:pharmacokinetics; D020719:Glucuronides / Q000652:urine; D006207:Half-Life; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009538:Nicotine / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine
chemical_list: D005731:Ganglionic Stimulants; D020719:Glucuronides; C066333:norcotinine; C001381:hydroxycotinine; D009538:Nicotine; D003903:Deuterium; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; D003367:Cotinine