title: Increased theophylline metabolism in the menstrual phase of healthy women.
abstract: BACKGROUND
  We previously reported on a Japanese woman with premenstrual asthma whose serum theophylline concentration was lower before the onset of her menstrual period. We evaluated the clearance of theophylline in each phase of her menstrual cycle and found an increase in clearance in the premenstrual and menstrual phases.
  
  
  OBJECTIVE
  This study was designed to investigate whether changes in theophylline clearance may occur with the menstrual cycle in nonasthmatic women.
  
  
  METHODS
  Aminophylline, 250 mg, was infused intravenously for 45 minutes, and the clearance of theophylline was calculated in seven healthy, ovulatory women on days 1 or 2, 10, and 20 or 25 of the menstrual cycle. The serum concentration of theophylline was determined with an enzyme immunoassay (homogeneous).
  
  
  RESULTS
  Theophylline clearance was significantly higher and its half-life was significantly shorter in the menstrual phase than in the follicular phase.
  
  
  CONCLUSIONS
  The metabolism of theophylline, and consequently, its clearance were increased in healthy women around the onset of menses. Clinicians must therefore consider the menstrual variation in theophylline metabolism when prescribing this drug to female patients.
authors.affiliation: The Third Department of Internal Medicine, Tottori University Faculty of Medicine, Yonago, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nagata
authors.forename: K
authors.initials: K
authors.lastname: Ishitobi
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: T
authors.initials: T
authors.lastname: Ikeda
authors.forename: S
authors.initials: S
authors.lastname: Hori
authors.forename: Y
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: T
authors.initials: T
authors.lastname: Sasaki
mesh_terms: D000328:Adult; D000628:Aminophylline / Q000008:administration & dosage / Q000493:pharmacokinetics; D005260:Female; D005498:Follicular Phase / Q000378:metabolism; D006207:Half-Life; D006801:Humans; D007262:Infusions, Intravenous; D008183:Luteal Phase / Q000378:metabolism; D008597:Menstrual Cycle / Q000097:blood / Q000378:metabolism*; D013806:Theophylline / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D000628:Aminophylline; D013806:Theophylline