Circulating levels of synthetic steroids in women using a ‘triphasic’ formulation: a comparison with different ethinyloestradiol doses

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Abstract
Summary Seventeen healthy women were given daily oral doses of ethinyloestradiol alone (30 or 50 μg day) or in combination with levonorgestrel (LNG) in a ‘triphasic’ regimen (30 μg ethinyloestradiol + 75 μg levonorgestrel, days 0-5; 40 μg ethinyloestradiol + 75 μg levonorgestrel, days 6-10; 30 μg ethinyloestradiol + 125 μg levonorgestrel, days 11-20). Serum samples were taken at frequent intervals for 28 days and the levels of unconjugated ethinyloestradiol and levonorgestrel estimated by radioimmunoassay. For the two groups taking ethinyloestradiol alone, the differences in serum levels between days 2 and 10 were significant and the mean level between days 10 and 19 was significantly lower in the 30 μg group compared to the 50 μg group. The area under the serum ethinyloestradiol concentration-time curve for the ‘triphasic’ group was intermediate between those of the 30 μg and 50 μg groups. Serum levonorgestrel increased slowly between days 0 and 10 and reached stable levels (1-2·5 ng/ml) on days 11-19