Introduction
Loestrin is a combination oral contraceptive containing ethinyl estradiol (an estrogen) and norethindrone acetate (a progestin). It is FDA-approved for pregnancy prevention and is also used for menstrual cycle regulation. Various formulations exist with different hormone strengths (e.g., Loestrin 1/20, Loestrin 1.5/30, Loestrin Fe 1/20).
Mechanism of Action
Loestrin works through multiple contraceptive mechanisms:
- Suppression of ovulation via negative feedback on hypothalamic-pituitary axis
- Cervical mucus thickening (progestin effect), creating a barrier to sperm penetration
- Endometrial alteration making implantation less likely
Indications
1. FDA-approved: Prevention of pregnancy 2. Off-label uses: - Treatment of moderate acne vulgaris in females ≥15 years old (specific formulations) - Management of dysmenorrhea - Regulation of menstrual cycles - Treatment of abnormal uterine bleeding
Dosage and Administration
Standard regimen: One tablet daily for 21 consecutive days followed by 7 hormone-free days (or 7 placebo tablets in Loestrin Fe formulations) Special populations:- Adolescents: Same as adult dosing after menarche
- Geriatric: Not indicated in postmenopausal women
- Renal impairment: No dosage adjustment required
- Hepatic impairment: Contraindicated in hepatic disease
- 1 missed pill: Take as soon as remembered
- 2 consecutive missed pills: Take 2 pills for 2 days, then resume regular schedule
- ≥3 consecutive missed pills: Discard pack, begin new pack on Sunday; use backup contraception for 7 days
Pharmacokinetics
Absorption:- Ethinyl estradiol: Extensive gastrointestinal absorption
- Norethindrone acetate: Rapidly converted to norethindrone; bioavailability ~65%
- Highly protein bound (ethinyl estradiol: 98% albumin-bound; norethindrone: SHBG and albumin-bound)
- Volume of distribution: Not well characterized
- Hepatic metabolism via CYP450 enzymes (primarily CYP3A4)
- Extensive first-pass metabolism
- Enterohepatic recirculation of ethinyl estradiol
- Ethinyl estradiol: Terminal half-life ~24 hours
- Norethindrone: Terminal half-life ~8 hours
- Excretion: Urine and feces
Contraindications
1. Current or history of thrombophlebitis or thromboembolic disorders 2. Known or suspected estrogen-dependent neoplasia 3. Undiagnosed abnormal genital bleeding 4. Known or suspected pregnancy 5. Current or history of cerebrovascular or coronary artery disease 6. Hepatic dysfunction or disease 7. Known or suspected breast carcinoma 8. Hypersensitivity to any component 9. Smokers over age 35 (>15 cigarettes/day)
Warnings and Precautions
Boxed Warning: Cigarette smoking increases risk of serious cardiovascular side effects; women over 35 who smoke should not use COCs Additional warnings:- Cardiovascular risks: Increased risk of MI, stroke, venous thromboembolism
- Hypertension: Monitor blood pressure regularly
- Gallbladder disease: May worsen existing disease
- Carbohydrate metabolism: May decrease glucose tolerance
- Lipid effects: May alter lipid profiles
- Liver disease: May worsen hepatic adenomas or carcinoma
- Depression: May exacerbate depression
- Lactation: May decrease milk production
Drug Interactions
Significant interactions:- Anticonvulsants: Carbamazepine, phenytoin, phenobarbital (decreased efficacy)
- Antimicrobials: Rifampin, griseofulvin (decreased efficacy)
- HIV medications: Protease inhibitors, NNRTIs (variable effects)
- St. John's Wort: Decreased contraceptive efficacy
- Anticoagulants: Potential alteration of warfarin effect
Adverse Effects
Common (≥5%):- Nausea
- Headache
- Breast tenderness
- Breakthrough bleeding
- Weight changes
- Mood changes
- Venous thromboembolism
- Myocardial infarction
- Stroke
- Hepatic adenomas
- Gallbladder disease
- Hypertension
Monitoring Parameters
Baseline:- Pregnancy test
- Blood pressure
- BMI
- Personal and family history
- Lipid profile (if indicated)
- Liver function tests (if indicated)
- Blood pressure every 6-12 months
- Annual comprehensive history and physical
- Symptom assessment for adverse effects
- Laboratory monitoring based on risk factors
Patient Education
Key points:- Take at same time daily for maximum effectiveness
- Use backup contraception during first 7 days of initial use
- Report severe abdominal pain, chest pain, headaches, visual changes, or leg pain immediately
- Smoking increases cardiovascular risks significantly
- Does not protect against HIV or other STIs
- May delay return to fertility after discontinuation
- Report missed periods or suspected pregnancy
- Inform all healthcare providers of Loestrin use
- Keep printed instructions readily available
- When in doubt, use backup contraception and consult healthcare provider
References
1. FDA Prescribing Information: Loestrin Fe 1/20 2. Curtis KM, Tepper NK, Jatlaoui TC, et al. U.S. Medical Eligibility Criteria for Contraceptive Use, 2016. MMWR Recomm Rep. 2016;65(3):1-103. 3. Teal S, Edelman A. Contraception Selection, Effectiveness, and Adverse Effects: A Review. JAMA. 2021;326(24):2507-2518. 4. Practice Bulletin No. 206: Use of Hormonal Contraception in Women with Coexisting Medical Conditions. Obstet Gynecol. 2019;133(3):e128-e150. 5. Stegeman BH, de Bastos M, Rosendaal FR, et al. Different combined oral contraceptives and the risk of venous thrombosis: systematic review and network meta-analysis. BMJ. 2013;347:f5298. 6. ACOG Practice Bulletin No. 110: Noncontraceptive uses of hormonal contraceptives. Obstet Gynecol. 2010;115(1):206-218.
This information is for educational purposes only and does not replace professional medical advice. Always consult with a healthcare provider for personalized medical guidance.