Levonorgestrel pharmacokinetics in plasma and milk of lactating women who take 1.5 mg for emergency contraception.
BACKGROUND
Progestin-only methods are among the contraceptive options available for breastfeeding women, however the doses of progestin used in emergency contraception (EC) have not been evaluated in nursing mothers. We therefore investigated the pharmacokinetics of 1.5 mg levonorgestrel (LNG) in lactating women.


METHODS
Twelve healthy exclusively breastfeeding volunteers received 1.5 mg LNG. Women refrained from nursing for 72 h after dosing and fed their infants with milk frozen beforehand. Serial blood and milk samples were collected for 120 h and assayed for LNG and sex hormone binding globulin.


RESULTS
LNG concentrations peaked in plasma and in milk 1-4 h and 2-4 h after dosing, respectively. Concentrations in milk (M) paralleled those in plasma (P) but were consistently lower (mean M:P ratio 0.28). Estimated infant exposure to LNG is 1.6 microg on the day of dosing (1 microg in the first 8 h), 0.3 microg on the second day and 0.2 microg on the third day.


CONCLUSIONS
Nursing mothers may need EC. These results suggest that to limit infant exposure to the period of maximum LNG excretion in milk, mothers should discontinue nursing for at least 8 h, but not more than 24 h, after EC.
Gainer
E
E
Laboratoire HRA Pharma, Paris 75003, France. e.gainer@hra-pharma.com
Massai
R
R
Lillo
S
S
Reyes
V
V
Forcelledo
M L
ML
Caviedes
R
R
Villarroel
C
C
Bouyer
J
J
D000293:Adolescent; D000328:Adult; D001942:Breast Feeding; D044363:Contraception, Postcoital; D003281:Contraceptives, Postcoital / Q000097:blood* / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007774:Lactation; D016912:Levonorgestrel / Q000097:blood* / Q000493:pharmacokinetics*; D008895:Milk, Human / Q000737:chemistry*; D012738:Sex Hormone-Binding Globulin / Q000032:analysis
D003281:Contraceptives, Postcoital; D012738:Sex Hormone-Binding Globulin; D016912:Levonorgestrel