Abstract
The present experiments were carried out to investigate the borderline dose for inhibition of ovulation by levonorgestrel and to study the mode of action of triphasic oral contraception. The borderline dose for inhibition of ovulation was found to be 50 µg levonorgestrel per day. In addition, bioavailability of levonorgestrel after daily oral administration of 50 µg and 100 µg, respectively, was recorded between 400 and 600 pg/ml serum. Daily ingestion of 150 µg levonorgestrel resulted in serum levels of 1 ng/ml. Two different preparations of a triphasic oral contraceptive were studied. The test preparations of a triphasic oral composition: SH B 264 AB: six coated tablets containing 30 µg of ethinyloestradiol and 50µg of levonorgestrel; five coated tablets containing 40µg of ethinyloestradiol and 75µg of levonorgestrel; and ten coated tablets containing 30 µg of ethinyloestradiol and 125 µg of levonorgestrel. SH B 261 AB: six coated tablets containing 30 µg of ethinyloestradiol and 50 µg of levonorgestrel; five coated tablets containing 50 ug of ethinyloestradiol and 50µg of levonorgestrel; and ten coated tablets containing 40 ug ethinyloestradiol and 125 µg of levonorgestrel. Serum levels of LH, 17β-oestradiol and progesterone were estimated by radioimmunoassay in five women receiving either SH B 264 AB or SH B 261 AB. In addition, the cervical score and the karyopyknotic index of vaginal smear samples were recorded. The data of the present investigation combine to suggest that triphasic oral contraception by SH B 264 AB acts by inhibiting ovulation and by providing a back-up mechanism by reducing the cervical score. The reduction oflevonorgestrel dose in SH B 264 AB does not interfere with cycle control, since the triphasic oral contraceptive very precisely mimics endogenous sex hormone serum levels of the normal cycle. Thus, patterns of endometrial hormone-receptor levels similar to those found in normal cycles are to be expected. The present preparation of this new generation of oral contraceptives is a well-balanced formulation providing greatest contraceptive safety and the least side-effects possible.
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Spona, J., Schneider, W.H.F., Lachnit-Fixson, U. (1980). Mode of action of triphasic oral contraception. In: Cortés-Prieto, J., Campos-da-Paz, A., Greenblatt, R.B. (eds) The Development of a New Triphasic Oral Contraceptive. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-6666-9_4
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DOI: https://doi.org/10.1007/978-94-011-6666-9_4
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