indication

For use as an oral contraceptive in the prevention of pregnancy.

pharmacology

Norethindrone is a synthetic oral progestin. It is used for contraception or to treat such conditions as secondary amenorrhea, abnormal uterine bleeding, and endometriosis. As an oral contraceptive, norethindrone is available as either a single agent or in combination with an estrogen.

mechanism of action

Progestins diffuse freely into target cells and bind to the progesterone receptor. Target cells include the female reproductive tract, the mammary gland, the hypothalamus, and the pituitary. Once bound to the receptor, progestins slow the frequency of release of gonadotropin releasing hormone (GnRH) from the hypothalamus and blunt the pre-ovulatory LH surge.

biotransformation

Hepatic

absorption

Absolute oral bioavailability approximately 64%

half life

7 hours

drug interactions

Acitretin: Acitretine may cause a loss of contraceptive effect

Amobarbital: This product may cause a slight decrease of contraceptive effect

Aprobarbital: This product may cause a slight decrease of contraceptive effect

Artemether: Artemether may decrease the effectiveness of norethindrone by increasing its metabolism via CYP3A4. Consider an alternate non-hormonal means of contraception during artemether therapy.

Bexarotene: Bexarotene may decrease the serum concentration of Contraceptives (Progestins). Since bexarotene is teratogenic and can lower serum concentrations of norethindrone, it is advised that women of childbearing potential use two forms of contraception (including at least one non-hormonal form).

Bosentan: Bosentan may decrease the contraceptive effect of norethindrone. Hormonal contraception should not be relied on alone during concomitant therapy with bosentan.

Butabarbital: This product may cause a slight decrease of contraceptive effect

Butalbital: This product may cause a slight decrease of contraceptive effect

Butethal: This product may cause a slight decrease of contraceptive effect

Carbamazepine: This product may cause a slight decrease of contraceptive effect

Colesevelam: Bile Acid Sequestrants may decrease the serum concentration of Contraceptives (Progestins). Administer oral progestin-containing contraceptives at least 1-4 hours prior to or 4-6 hours after administration of a bile acid sequestrant. Consider alternatives in order to avoid this combination when possible, due to the risk for impaired contraceptive effectiveness.

Ethotoin: This product may cause a slight decrease of contraceptive effect

Fosphenytoin: This product may cause a slight decrease of contraceptive effect

Griseofulvin: This product may cause a slight decrease of contraceptive effect

Heptabarbital: This product may cause a slight decrease of contraceptive effect

Hexobarbital: This product may cause a slight decrease of contraceptive effect

Lamotrigine: The oral contraceptive decreases the effect of lamotrigine

Mephenytoin: This product may cause a slight decrease of contraceptive effect

Methohexital: This product may cause a slight decrease of contraceptive effect

Methylphenobarbital: This product may cause a slight decrease of contraceptive effect

Pentobarbital: This product may cause a slight decrease of contraceptive effect

Phenobarbital: This product may cause a slight decrease of contraceptive effect

Phenytoin: This product may cause a slight decrease of contraceptive effect

Pioglitazone: Possible loss of contraceptive effect

Primidone: This product may cause a slight decrease of contraceptive effect

Rifabutin: Rifabutin may decrease the contraceptive effect of norethindrone. Hormonal contraception should not be solely relied on alone during concomitant therapy with rifabutin.

Rifampin: This product may cause a slight decrease of contraceptive effect

Rifapentine: This product may cause a slight decrease of contraceptive effect

Secobarbital: This product may cause a slight decrease of contraceptive effect

St. John's Wort: St. John's Wort could reduce the contraceptive effect

Talbutal: This product may cause a slight decrease of contraceptive effect

Thiopental: Thiopental may decrease the effect of Norethindrone. Contraceptive failure may occur. Alternative nonhomomonal contraception should be used during concomitant therapy.

Tizanidine: The contraceptive increases the effect of tizanidine

Tretinoin: Oral Tretinoin may decrease the effect of oral contraceptive, Norethindrone. An alternate form of contraception should be used during concomitant therapy.

Troglitazone: Possible loss of contraceptive effect

Warfarin: Norethindrone may alter the anticoagulant effect of warfarin. Concomitant therapy should be avoided. Monitor for changes in coagulation status if norethindrone is initiated, discontinued or dose changed.