Usage
Levonorgestrel is primarily prescribed for emergency contraception to prevent pregnancy after unprotected intercourse or contraceptive failure. It is also used in some regular contraceptive pills, hormonal intrauterine devices (IUDs), and implants. It’s classified as a progestogen, a synthetic form of the naturally occurring female hormone progesterone. Levonorgestrel primarily works by preventing ovulation (release of an egg from the ovary). It also thickens cervical mucus, making it difficult for sperm to enter the uterus and reach the egg, and may alter the uterine lining, making implantation less likely.
Alternate Names
Levonorgestrel is also known as the “morning-after pill.” Popular brand names include Plan B One-Step, Next Choice One Dose, My Way, Take Action, and others. Several combined oral contraceptives also contain levonorgestrel, often in combination with ethinyl estradiol.
How It Works
Pharmacodynamics: Levonorgestrel primarily acts by binding to progesterone receptors in the body, mimicking the effects of progesterone. This leads to suppression of the luteinizing hormone (LH) surge, which is essential for ovulation. The thickening of cervical mucus and changes in the uterine lining are also mediated by progesterone receptor binding.
Pharmacokinetics:
- Absorption: Levonorgestrel is rapidly and completely absorbed after oral administration, reaching peak plasma concentrations in about 1-2 hours.
- Metabolism: It is primarily metabolized in the liver by CYP3A4 enzymes, resulting in inactive metabolites.
- Elimination: Levonorgestrel is eliminated through both urine and feces, with a half-life of approximately 25-30 hours.
Mode of Action: At the molecular level, levonorgestrel binds to progesterone receptors in target tissues, such as the hypothalamus, pituitary gland, cervix, and uterus. This binding modulates gene expression, leading to the observed effects on ovulation, cervical mucus, and the endometrium.
Dosage
Standard Dosage
Adults: For emergency contraception, a single dose of 1.5 mg taken orally as soon as possible within 72 hours of unprotected intercourse. Alternatively, two doses of 0.75 mg can be taken, 12 hours apart.
Children: The same dosage as adults can be used in adolescents. Use in younger children should be guided by clinical considerations.
Special Cases:
- Elderly Patients: No specific dosage adjustments are typically required, but clinical judgment is important.
- Patients with Renal Impairment: No specific dosage adjustments are typically required.
- Patients with Hepatic Dysfunction: Use with caution in patients with severe liver disease. Dose adjustments may be considered.
- Patients with Comorbid Conditions: No specific adjustments are generally recommended, but individual patient factors should be considered.
Clinical Use Cases
Levonorgestrel is not typically used in clinical settings like intubation, surgical procedures, mechanical ventilation, or the ICU. Its primary use is for emergency contraception.
Dosage Adjustments
Dose adjustments are required for patients taking enzyme-inducing medications like rifampicin, phenytoin, and some antiretroviral drugs. In such cases, a higher dose of levonorgestrel (3 mg) may be needed.
Side Effects
Common Side Effects:
- Nausea
- Vomiting
- Abdominal pain
- Fatigue
- Headache
- Dizziness
- Breast tenderness
- Menstrual changes (irregular bleeding, spotting)
Rare but Serious Side Effects:
- Allergic reactions (rash, itching, swelling)
- Ectopic pregnancy (pregnancy outside the uterus)
Long-Term Effects: No significant long-term effects are associated with the use of levonorgestrel for emergency contraception.
Contraindications
- Known or suspected pregnancy
- Hypersensitivity to levonorgestrel
Drug Interactions
Enzyme-inducing drugs (e.g., rifampicin, phenytoin, carbamazepine, some antiretrovirals) can reduce the effectiveness of levonorgestrel. Herbal supplements containing St. John’s Wort should also be avoided.
Pregnancy and Breastfeeding
Levonorgestrel is not recommended during pregnancy as it is not effective once implantation has occurred. While limited data suggest no significant adverse effects on the fetus when used early in pregnancy, it’s best to avoid use. Levonorgestrel is excreted in breast milk, but limited information suggests minimal risk to the nursing infant.
Drug Profile Summary
- Mechanism of Action: Prevents ovulation, thickens cervical mucus, and alters the endometrium.
- Side Effects: Nausea, vomiting, abdominal pain, fatigue, headache, menstrual changes.
- Contraindications: Known or suspected pregnancy, hypersensitivity.
- Drug Interactions: Enzyme-inducing drugs.
- Pregnancy & Breastfeeding: Avoid use during pregnancy. Use with caution during breastfeeding.
- Dosage: 1.5 mg single dose or 0.75 mg 12 hours apart.
- Monitoring Parameters: Not routinely required for emergency contraception.
Popular Combinations
Levonorgestrel is combined with ethinyl estradiol in many regular contraceptive pills.
Precautions
- General Precautions: Rule out pregnancy before use.
- Specific Populations: Not for routine contraception.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Levonorgestrel for emergency contraception?
A: A single 1.5 mg dose or two 0.75 mg doses taken 12 hours apart.
Q2: How effective is Levonorgestrel?
A: It’s most effective when taken within 24 hours of unprotected intercourse, reducing the risk of pregnancy by up to 89%. Effectiveness decreases with time.
Q3: Can Levonorgestrel be used as regular birth control?
A: No, it’s only for emergency contraception.
Q4: What are the common side effects?
A: Nausea, vomiting, abdominal pain, headache, and menstrual changes are common.
Q5: Can Levonorgestrel terminate an existing pregnancy?
A: No. Levonorgestrel will not harm an existing pregnancy, but it’s ineffective once implantation has occurred.
Q6: Are there any drug interactions I should be aware of?
A: Yes, enzyme-inducing medications can reduce its effectiveness.
Q7: What should I do if I vomit after taking Levonorgestrel?
A: If vomiting occurs within 2 hours of taking the medication, consider repeating the dose. Consult a healthcare professional if needed.
Q8: How often can I take Levonorgestrel?
A: While it can be used multiple times, it shouldn’t be relied upon as regular contraception.
Q9: Can Levonorgestrel cause birth defects if I take it and I am already pregnant?
A: Current evidence suggests no increased risk of birth defects. However, it’s not recommended during pregnancy.
Q10: How soon can I start regular birth control after taking Levonorgestrel?
A: You can start regular birth control immediately after taking Levonorgestrel.
