Transfer of norethisterone(NET) and levonorgestrel(LNG) from a singie tablet into the infant's circulation through the mother's milk

A single tablet of either of the three different types of oral contraceptive preparations, viz. “Gynovlar” containing 3000 ug norethisterone (NET) and 50 ug ethinyl estradiol (EE₂) or “Ovral” containing 250 ug levonorgestrel (LNG) and 50 ug EE₂, or a daily progestogen only type — “Minipill” containing 30 ug of LNG only, were administered to 40 normal lactating women on a random basis. The sampling schedule in all the three body fluids, i.e. the maternal sera, breast milk and the infant's sera, was kept in such a manner that the peak levels of the contraceptive steroids would be expected to be present in these fluids. The results of this study indicate that the transfer ratio of LNG or NET from the maternal sera to her breast milk was approximately 10% (6–34%) for Gynovlar, 9% (5–18%) for Ovral and 6% (2–34%) for Minipill. However, it was interesting to observe that whereas the transfer ratio of NET or LNG from breast milk to infant's sera was similar for combination pills — 8% (3–23%) for Gynovlar and 12% (3–42%) for Ovral, it was significantly higher for progestogen only Minipills — 38% (13–92%) for LNG. The precise reason for the higher transfer ratio of LNG from breast milk to infant's serum in Minipill users cannot be explained.     

Release of 19-nor-testosterone type of contraceptive steroids through different drug delivery systems into serum and breast milk of lactating women

The release of contraceptive steroids through different drug delivery systems into serum and breast milk was investigated in a group of lactating women. Four women in each group were taking either a low dosage progestogen compound like norethisterone (NET) 350 μg or d-norgestrel (d-Ng) 50 μg alone or low dosage combination pills containing NET 1 mg or d-Ng 150 μg with 30 μg ethinyl estradiol (EE₂) or a biodegradable implant containing 25 mg NET or d-Ng. Peak levels in plasma and milk were seen in oral contraceptive users around 2 hours. Of the two low dosage progestogen compounds, d-Ng was below the detection limit in milk within 4 hours whereas NET was still detectable at the 24-hour interval. In contrast to this, because of the larger quantity of steroids in the combination pills, the NET/d-Ng levels in serum as well as in milk were high throughout the 24-hour period. With the subdermal route because of the sustained low release of the drug from the biodegradable implants, the levels in milk were below the detection limit within a day with d-Ng and within a week with NET.