title: The pharmacokinetics of sumatriptan when administered with clarithromycin in healthy volunteers.
abstract: BACKGROUND
  Macrolide antibiotics such as clarithromycin are potent inhibitors of the cytochrome P450 (CYP)3A4 isozyme and have the potential to attenuate the metabolism and increase blood concentrations of drugs metabolized by this pathway. In vitro studies have suggested that sumatriptan is metabolized primarily by the monoamine oxidase-A isozyme and not by CYP3A4.
  
  
  OBJECTIVE
  This study sought to determine the effect of coadministration of clarithromycin dosed to steady state on the pharmacokinetics of a single dose of sumatriptan. A secondary objective was to assess the safety and tolerability of combining these agents.
  
  
  METHODS
  This was an open-label, randomized, 2-way crossover study in healthy volunteers. During treatment period 1, subjects received either a single oral dose of sumatriptan 50 mg (sumatriptan alone) or clarithromycin 500 mg orally every 12 hours on days 1 to 3 and a single oral dose of sumatriptan 50 mg plus a single oral dose of clarithromycin 500 mg on the morning of day 4 (combination treatment). During treatment period 2, they received the alternative regimen. Equivalence between sumatriptan alone and combination treatment was concluded if the 90% CI for the ratio of reference to test means of loge-transformed data for area under the plasma concentration-time curve extrapolated to infinity (AUC(infinity)) and maximum plasma concentration (Cmax) fell within the interval from 0.8 to 1.25.
  
  
  RESULTS
  In the 24 evaluable subjects (12 men, 12 women) included in the pharmacokinetic analysis, mean sumatriptan AUC(infinity) and Cmax values after administration of combination treatment were 9% and 14% higher, respectively, than the corresponding values after administration of sumatriptan alone. The 90% CI for the ratio of reference to test means for AUC(infinity) was 1.03 to 1.15. The 90% CI for the ratio of reference to test means for Cmax was 1.03 to 1.26, above the traditional bioequivalence criterion. All other pharmacokinetic parameters tested, including nonparametric analysis of the time to Cmax, met the criterion for equivalence between treatments. Both treatments were well tolerated in the 27 subjects (13 men, 14 women) included in the safety analysis.
  
  
  CONCLUSIONS
  The extent of absorption of sumatriptan was similar after oral administration alone and in combination with clarithromycin dosed to steady state. These data are consistent with previous reports that sumatriptan is unaffected by coadministration with the potent CYP3A4 inhibitor clarithromycin, supporting concomitant administration of these agents without the need for dose adjustment of sumatriptan in the acute treatment of migraine.
authors.affiliation: Clinical Pharmacology and Experimental Medicine, GlaxoSmithKline, Research Triangle Park, North Carolina 27709-3398, USA. km10993@gsk.com
authors.forename: Katy H P
authors.initials: KH
authors.lastname: Moore
authors.forename: Philip T
authors.initials: PT
authors.lastname: Leese
authors.forename: Scott
authors.initials: S
authors.lastname: McNeal
authors.forename: Peter
authors.initials: P
authors.lastname: Gray
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Quinn
authors.forename: Carole
authors.initials: C
authors.lastname: Bye
authors.forename: Mark
authors.initials: M
authors.lastname: Sale
mesh_terms: D000293:Adolescent; D000328:Adult; D000900:Anti-Bacterial Agents / Q000009:adverse effects*; D019540:Area Under Curve; D017291:Clarithromycin / Q000009:adverse effects*; D018592:Cross-Over Studies; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004347:Drug Interactions; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017366:Serotonin Receptor Agonists / Q000009:adverse effects / Q000493:pharmacokinetics*; D018170:Sumatriptan / Q000009:adverse effects / Q000493:pharmacokinetics*
chemical_list: D000900:Anti-Bacterial Agents; D017366:Serotonin Receptor Agonists; D018170:Sumatriptan; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D017291:Clarithromycin