norethindrone Pharmacologic classification: progestin
Aygestin, Norlutate ◆
Therapeutic classification: contraceptive
Pregnancy risk category X
Available by prescription only
Tablets: 0.35 mg
Tablets: 5 mg
Indications and dosages
Amenorrhea, abnormal uterine bleeding, endometriosis. Adults: 2.5 to 10 mg norethindrone acetate P.O. daily on days 5 to 10 of second half of menstrual cycle.
Endometriosis. Adults: 5 mg norethindrone acetate P.O. daily for 14 days; then increase by 2.5 mg/day q 2 weeks up to 15 mg/day. May continue daily
therapy consecutively for 6 to 9 months; if breakthrough bleeding occurs, temporarily discontinue therapy.
Contraception. Adults: 0.35 mg norethindrone P.O. daily, beginning day 1 of menstrual cycle and continuing uninterrupted thereafter.
Contraceptive action: Norethindrone suppresses ovulation, causes thickening of cervical mucus, and induces sloughing of the endometrium.
Absorption: Well absorbed after oral administration.
Distribution: Distributed into bile and breast milk and is about 80% protein-bound.
Metabolism: Primarily metabolized in the liver, where it undergoes extensive first-pass metabolism.
Excretion: Excreted primarily in feces. Elimination half-life is 5 to 14 hours.
Contraindications and precautions
Contraindicated in pregnant women, patients hypersensitive to drug, and patients with thromboembolic disorders, cerebral
apoplexy, or history of these conditions; breast cancer; undiagnosed abnormal vaginal bleeding; severe hepatic disease; or
Use cautiously in patients with diabetes mellitus, seizures, migraine, cardiac or renal disease, asthma, or mental depression.
Drug-drug. Anti-infectives, phenytoin, carbamazepine, phenobarbital, rifampin: Decreases effectiveness of norethindrone. Advise patient to report signs of decreased effectiveness and to use an alternative form of contraception.
Bromocriptine: Causes amenorrhea or galactorrhea, which interferes with the action of bromocriptine. Don’t use together.
Drug-herb. St. John’s wort: Decreases effectiveness of hormonal contraceptives. Discourage use together.
CNS: depression, CVA.
CV: thrombophlebitis, edema, thromboembolism.
EENT: exophthalmos, diplopia, retinal thrombosis.
GU: breakthrough bleeding, dysmenorrhea, amenorrhea, cervical erosion, abnormal secretions.
Hepatic: cholestatic jaundice.
Metabolic: changes in weight.
Respiratory: pulmonary embolism.
Skin: melasma, rash, acne, pruritus.
Other: breast tenderness, enlargement, or secretion.
Effects on lab test results
May increase amino acid levels.
May increase liver function test values. May decrease pregnanediol excretion and glucose tolerance.
Overdose and treatment
No information available.
ALERT Don’t confuse Micronor with Micro K or Micronase.
ALERT Norethindrone acetate is twice as potent as norethindrone. Norethindrone acetate shouldn’t be used for contraception.
Use as a test for pregnancy isn’t appropriate; drug may cause birth defects and masculinization of female fetus.
Preliminary estrogen treatment is usually needed in menstrual disorders.
Monitor liver function test results in patients with hepatic impairment.
Observe patient for signs of edema.
Explain possible adverse effects of progestins before patient takes first dose. Also, urge patient to carefully read package
insert before taking drug.
Tell patient to take drug at same time every day when used as a contraceptive.
ALERT Tell patient to report unusual symptoms immediately and to stop drug and call if visual disturbances or migraine occurs.
Teach woman how to perform routine breast self-examination.
Tell patient to report suspected pregnancy.
Tell patient with visual disturbances or migraine to stop drug and call immediately.
If using as a method of contraception, tell patient that risk of pregnancy increases with each tablet missed. If she misses
one tablet, tell her to take it as soon as she remembers and then take the next tablet at the regular time. If she misses
two tablets, tell her to take one as soon as she remembers, take the next regular dose at the usual time, and use a nonhormonal
method of contraception in addition to norgestrel until 14 tablets have been taken. If she misses three or more tablets, tell
her to discontinue drug and use a nonhormonal method of contraception until after her menstrual period. Instruct patient to
perform a pregnancy test if her menstrual period doesn’t occur within 45 days.
Advise patient to use another method of contraception until after the first week of administration in the initial cycle if
drug was begun on the first Sunday after menstruation. This isn’t needed if drug was initiated on the first day of menstruation.
Reactions may be common, uncommon, life-threatening, or
COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use