Ethinyl estradiol/norethisterone

Ethinyl estradiol/norethisterone
Combination of
Ethinyl estradiol Estrogen
Norethisterone acetate Progestogen
Clinical data
Trade names Junel, Loestrin, Microgestin
AHFS/Drugs.com Monograph
MedlinePlus a601050
License data
Pregnancy
category
  • US: X (Contraindicated)
Routes of
administration		 Oral
Legal status
Legal status
ChemSpider none

Ethinyl estradiol/norethisterone (trade names Junel, Loestrin, Microgestin, and others) is a combined oral contraceptive pill.

Pharmacology

Its combination oral contraceptives act by suppression of gonadotropins. Although the primary mechanism of this action is inhibition of ovulation, other alterations include changes in the cervical mucus, which increase the difficulty of sperm entry into the uterus and the endometrium, which reduce the likelihood of implantation. The absorption of norethisterone acetate appears to be completely and rapidly deacetylated to norethisterone after oral administration, since the disposition of norethisterone acetate is indistinguishable from that of orally administered norethisterone. Norethisterone acetate and ethinyl estradiol are subject to first-pass metabolism after oral dosing, resulting in an absolute bioavailability of approximately 64% for norethisterone and 43% for ethinyl estradiol.[1]

Norethisterone undergoes extensive biotransformation, primarily via reduction, followed by sulfate and glucuronide conjugation. The majority of metabolites in the circulation are sulfates, with glucuronides accounting for most of the urinary metabolites.[2] A small amount of norethisterone acetate is metabolically converted to ethinyl estradiol. Ethinyl estradiol is also extensively metabolized, both by oxidation and by conjugation with sulfate and glucuronide. Sulfates are the major circulating conjugates of ethinyl estradiol and glucuronides predominate in urine . The primary oxidative metabolite is 2-hydroxy ethinyl estradiol, formed by the CYP3A4 isoform of cytochrome P450. Part of the first-pass metabolism of ethinyl estradiol is believed to occur in gastrointestinal mucosa. Ethinyl estradiol may undergo enterohepatic circulation.[2]

Indications

Junel is approved by the U.S. Food and Drug Administration (FDA) for the prevention of pregnancy.

See also

References

  1. ↑ Back DJ, Breckenridge AM, Crawford FE, McIver M, Orme M. L'E, Rowe PH, Smith E (1978). "Kinetics of norethindrone in women; II. Single-dose kinetics". Clinical Pharmacology & Therapeutics. 24 (4): 448–453. doi:10.1002/cpt1978244448. ISSN 0009-9236.
  2. 1 2 K, Fotherby (1999). Pharmacokinetics and metabolism of progestins in humans, in Pharmacology of the contraceptive steroids,. New York: Raven Press,.


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