Data concerning ethinylestradiol (EE) blood levels among 93 healthy women using oral contraceptives are presented. Seventy-two per cent of the observed variation in EE blood levels was unexplainable on the basis of time since ingestion of the last oral contraceptive, day of menstrual cycle, race, age, weight, height, blood pressure, cigarette consumption, alcohol consumption, diurnal variation, or lifetime use of oral contraceptives.
PIP: This 2-fold investigation studied 1) the extent to which women vary in blood levels of ethinylestradiol (EE) after ingesting oral contraceptives (OCs) containing similar amounts of EE or mestranol (ME), which is metabolized to EE; and 2) whatever variations might be accountable on the basis of physical, behavioral, or other characteristics. 93 healthy OC users were given either OCs with 50 mcg of ME (84 subjects) of 50 mcg of EE (9 subjects). Linear regression was used to determine relevance of variation in EE blood levels based on hours since pill ingestion, day of menstrual cycle, or any other variables. Hours since OC showed the strongest relationship to log EE, accounting for 25% of the variation. Another 3% could be accounted for by day of menstrual cycle. The remaining 72% of observed variation in EE levels could not be explained in terms of time since ingestion of last OC, day of menstrual cycle, race, age, weight, height, or use-duration of OCs.