J Clin Pharmacol. 1999 Sep;39(9):936-40.  

Inhibition of caffeine metabolism by estrogen replacement therapy in
postmenopausal women.

Pollock BG, Wylie M, Stack JA, Sorisio DA, Thompson DS, Kirshner MA, Folan MM,
Condifer KA.

Geriatric Psychopharmacology Program, Western Psychiatric Institute and Clinic,
Pittsburgh, PA 15213, USA.

This study was conducted to investigate the effect of therapeutic estrogen on
cytochrome P450 1A2-mediated metabolism in postmenopausal women using caffeine
as a model substrate. Twelve healthy postmenopausal women underwent estrogen
replacement therapy in the form of estradiol (Estrace). Estradiol was initiated
at a dose of 0.5 mg a day and titrated to achieve a steady-state plasma
concentration of 50 to 150 pg/ml. Caffeine metabolic ratios (CMR;
paraxanthine/caffeine) were assessed both before and after 8 weeks of estrogen
replacement. For the 12 subjects, there was a mean reduction in CMR of -29.2 +/-
25.0 (p = 0.0019). Consistent with previous results found in younger women,
these results indicate that exogenous estrogen in older women may inhibit
CYP1A2-mediated caffeine metabolism.

Publication Types:
    Clinical Trial

PMID: 10471985 [PubMed - indexed for MEDLINE]