Norethindrone

Pronunciation

(nor eth IN drone)

U.S. Brand Names

Aygestin®; Camila™; Errin™; Jolivette™; Micronor®; Nora-BE™; Nor-QD®

Synonyms

Norethindrone Acetate; Norethisterone

Generic Available

Yes

Canadian Brand Names

Micronor®; Norlutate®

Use

Treatment of amenorrhea; abnormal uterine bleeding; endometriosis, oral contraceptive; higher rate of failure with progestin only contraceptives

Pregnancy Risk Factor

Lactation

Enters breast milk/use caution

Contraindications

Hypersensitivity to norethindrone or any component of the formulation; thromboembolic disorders; severe hepatic disease; breast cancer; undiagnosed vaginal bleeding; pregnancy

Warnings/Precautions

Use of any progestin during the first 4 months of pregnancy is not recommended. Discontinue if sudden partial or complete loss of vision, proptosis, diplopia, or migraine occur. There is a higher rate of failure with progestin only contraceptives . Progestin-induced withdrawal bleeding occurs within 3-7 days after discontinuation of drug. Use with caution in patients with asthma, diabetes, seizure disorder, hyperlipidemias, migraine, cardiac or renal dysfunction, or psychic depression.

Adverse Reactions

>10%:

Cardiovascular: Edema

Endocrine & metabolic: Breakthrough bleeding, spotting, changes in menstrual flow, amenorrhea

Gastrointestinal: Anorexia

Local: Pain at injection site

Neuromuscular & skeletal: Weakness

1% to 10%:

Cardiovascular: Edema

Central nervous system: Mental depression, fever, insomnia

Dermatologic: Melasma or chloasma, allergic rash with or without pruritus

Endocrine & metabolic: Increased breast tenderness

Gastrointestinal: Weight gain/loss

Genitourinary: Changes in cervical erosion and secretions

Hepatic: Cholestatic jaundice

Drug Interactions

Substrate of CYP3A4 (major); Induces CYP2C19 (weak)

Aminoglutethimide: May decrease norethindrone effects by increasing hepatic metabolism

CYP3A4 inducers: CYP3A4 inducers may decrease the levels/effects of norethindrone. Example inducers include aminoglutethimide, carbamazepine, nafcillin, nevirapine, phenobarbital, phenytoin, and rifamycins.

Nelfinavir: Decreases norethindrone concentrations

Rifampin: May decrease effect of norethindrone

Ethanol/Nutrition/Herb Interactions

Food; Limit caffeine.

Herb/Nutraceutical: High-dose vitamin C (1 g/day) may increase adverse effects. Avoid St John's wort.

Mechanism of Action

Inhibits secretion of pituitary gonadotropin (LH) which prevents follicular maturation and ovulation

Pharmacodynamics/Kinetics

Absorption: Oral, transdermal: Rapidly absorbed

Distribution: Vd: 2-4 L/kg

Protein binding: 61% to albumin; 36% to sex hormone-binding globulin (SHBG); SHBG capacity affected by plasma ethinyl estradiol levels

Metabolism: Oral: Hepatic via reduction and conjugation; first-pass effect

Bioavailability: 64%

Half-life elimination: 5-14 hours

Time to peak: 1-2 hours

Excretion: Primarily urine (as metabolites)

Dosage

Oral: Adolescents and Adults: Female:

Contraception: Progesterone only: Norethindrone 0.35 mg every day of the year starting on first day of menstruation; if one dose is missed, discontinue and use an alternative method of contraception

Amenorrhea and abnormal uterine bleeding:

Norethindrone: 5-20 mg/day for 5-10 days during the second half of the menstrual cycle

Acetate salt: 2.5-10 mg/day for 5-10 days during the second half of the menstrual cycle

Endometriosis:

Norethindrone: 10 mg/day for 2 weeks; increase at increments of 5 mg/day every 2 weeks until 30 mg/day; continue for 6-9 months or until breakthrough bleeding demands temporary termination

Acetate salt: 5 mg/day for 14 days; increase at increments of 2.5 mg/day every 2 weeks up to 15 mg/day; continue for 6-9 months or until breakthrough bleeding demands temporary termination

Dietary Considerations

Should be taken with food at same time each day.

Patient Education

Take according to prescribed schedule. Follow instructions for regular self-breast exam. You may experience dizziness or lightheadedness; use caution when driving or engaging in tasks that require alertness until response to drug is known. Limit intake of caffeine. Avoid high-dose vitamin C. You may experience photosensitivity; use sunscreen, wear protective clothing and eyewear, and avoid direct sunlight. You may experience loss of hair (reversible), swelling of hands or feet, weight gain or loss. Report sudden severe headache or vomiting, disturbances of vision or speech, sudden blindness, numbness of weakness in an extremity, chest pain, calf pain, respiratory difficulty, weight gain >5 lb/week, depression or acute fatigue, unusual bleeding, spotting, or changes in menstrual flow. Pregnancy/breast-feeding precautions: Inform prescriber if you are pregnant. Consult prescriber if breast-feeding.

Nursing Implications

Norethindrone acetate is ~2 times as potent as norethindrone

Dental Health: Effects on Dental Treatment

Until we know more about the mechanism of interaction, caution is required in prescribing antibiotics to female dental patients taking progestin-only hormonal contraceptives.

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

May cause insomnia or depression

Mental Health: Effects on Psychiatric Treatment

None reported

Dosage Forms

Tablet (Camila™, Errin™, Jolivette™, Micronor®, Nora-BE™, Nor-QD®): 0.35 mg

Tablet, as acetate (Aygestin®): 5 mg

International Brand Names

Aminor® (EG, JO, KW, LB, SY); Conludag® (NO); Locilan 28 Day® (AU); Megestran® (BR); Menzol® (GB); Micronor® (AU, BR, CA, EG, GB, JO, LB, MT, SY); Micro-Novium® (ZA); Micronovum® (AT, CH); Mini-Pe® (DK, SE); Mini-Pill® (FI); Monogest® (CZ); Norcolut® (BD, HU, RU, SG); Norcutin® (BD); Norelut® (ID); Norestin® (BR); Norethisterone Beacons® (SG); Norethisterone® (CY, GB); Norethisterone Malchem® (SG); Noriday 28® (AU, NZ); Noriday® (CY, EG, GB, IE, JO, KW, LB, MT, SY); Noriday Orifarm® (DK); Norlutate® (CA); Primolut N® (AU, CH, CN, CY, EG, FI, GB, ID, IE, IN, JO, KW, LB, NL, NO, NZ, SG, TH, ZA); Steron® (TH); Utovlan® (CY, EG, GB, JO, KW, LB, MT, SY)

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