Interactions of medroxyprogesterone acetate with estrogen on the calcium-parathyroid axis in post-menopausal women

We studied the effect of medroxyprogesterone acetate (MPA) as a single agent and in combination with conjugated equine estrogens (E), on the calcium-parathyroid axis in healthy post-menopausal women. Twenty-six subjects, 2-22 yr post-menopause, were studied under basal conditions, and then following 10 days of MPA (10 mg/day), 30 days of E (0.625 or 1.25 mg/day), and an additional 10 days of E + MPA. As predicted, E decreased urinary excretion of calcium and hydroxyproline. MPA did not alter these excretion variables, either when given alone, or when added to E. Cyclic administration of MPA for 10 days is currently advocated to avoid the adverse endometrial consequences of unopposed estrogen. These data indicate that such a program does not interfere with the beneficial effect of estrogen on the calcium-parathyroid axis.