Levonorgestrel

Mechanism of Action

Levonorgestrel (LNG—17alpha-ethynyl-18-methylestr-4-en-17beta-ol-3-one) is a second-generation synthetic progestogen that is the active component of the racemic mixture of norgestrel. It binds to progesterone and androgen receptors, which can delay the release of gonadotropin-releasing hormone from the hypothalamus. This action blunts the luteinizing hormone surge that occurs during the pre-ovulation stage. Ultimately, it can delay or inhibit ovulation by preventing fertilization via inhibiting follicular rupture and releasing a viable egg from the ovaries. Optimal efficacy is also achievable when it is taken in the pre-ovulation stage. Levonorgestrel also induces the thickening of cervical mucus, which helps by interfering with sperm motility and passage. There has been no evidence in recent studies that levonorgestrel significantly affects the endometrium to alter it to prevent pregnancy.[4]

Studies have shown that levonorgestrel is not subject to significant first-pass metabolism. Levonorgestrel undergoes metabolism via hydroxylation, conjugation, and reduction in the liver. Its bioavailability varies from 85% to 100%.[5]

Administration

For emergency contraceptive use, the recommended dose is 1.5 mg oral tablet within 72 hours.  If taken within 72 hours after unprotected sex, levonorgestrel can reduce the risk of pregnancy by up to 87%. If taken within 24 hours, the efficacy is higher. There is also a 0.75 mg oral tablet that can be given with a second 0.75 mg dose if needed 24 hours later. A 3 mg oral levonorgestrel is for patients concomitantly taking a CYP3A4 cytochrome p450 liver enzyme-inducing drug, eg, rifampicin, St. John’s wort, carbamazepine, or phenobarbital due to these agents increasing hepatic clearance of levonorgestrel. Vomiting can occur within two hours of administration, at which case the patient would need to repeat the initial dose taken.[6]

For long-term birth control options, the levonorgestrel intrauterine T-shaped device has 52 mg of levonorgestrel covered by a rate-controlling membrane that regulates the rate of release of hormones.[3] The combined oral contraceptive pill with ethinylestradiol comes in a 21-pill pack per month with 0.1 mg of levonorgestrel and 0.02 mg of ethinylestradiol.

Adverse Effects

For the emergency contraceptive, the timing of when patients ingest the drug plays a significant role in its efficacy in preventing pregnancy; this means the adverse effect of pregnancy occurring becomes greater when the patient waits over 48 to 72 hours or longer to take the drug as well as taking the medication during an ovulation cycle. Many studies have shown an efficacy reduction in women whose BMI is greater than 30 kg/m², but not significant enough to restrict this subset of patients from using levonorgestrel, which appears to be due to the lower bioavailability of a standard 1.5 mg dose given of levonorgestrel, free plus albumin-bound, in these patients. The most common side effects are menstrual abnormalities, amenorrhea, dysmenorrhea, oligomenorrhea, headaches, and acne. Other side effects that can occur are nausea and vomiting. Importantly, this drug does not protect any patient from sexually transmitted infections and diseases, and the advice to patients is to use condoms for protection.[7][8]

For the intrauterine device, 0.1% of pregnancy occurs within the first year of use. The intrauterine device most commonly causes menstrual irregularities, including amenorrhea and oligomenorrhea. Other side effects of the intrauterine device are similar to those of the combined oral contraceptive pill route, such as ovarian cysts, weight gain, depression, acne, and low libido.[3]

Drug-Drug Interactions

The following may diminish the therapeutic effect of progestins: acitretin, anticoagulants, antidiabetic agents, barbiturates, carbamazepine, fosphenytoin, griseofulvin, mifepristone, phenytoin, primidone, retinoic acid derivatives, and St. John's wort.

The following may decrease the serum concentration of progestins: aprepitant, artemether, bexarotene, bile acid sequestrants, bosentan, brigatinib, clobazam, CYP3A4 inducers, dabrafenib, darunavir, efavirenz, encorafenib, eslicarbazepine, exenatide, felbamate, fosaprepitant,  ixazomib, lamotrigine, lesinurad, lixisenatide, lopinavir, lorlatinib, lumacaftor, metreleptin, mycophenolate, nelfinavir, nevirapine, oxcarbazepine, perampanel, rifamycin derivatives, saquinavir, sugammadex, and topiramate.

The following may increase the serum concentration of progestins: atazanavir, cobicistat, tipranavir, and voriconazole. 

The following may enhance the thrombogenic effect of progestins: C1-inhibitors and carfilzomib.

Contraindications

There are several contraindications for the emergency contraceptive form, including allergy, hypersensitivity, severe liver disease, pregnancy, and drug-drug interactions with liver enzyme-inducing drugs.[9]

For the intrauterine device, the contraindications include uterine anomalies (fibroids, cysts), breast carcinoma, active cervicitis/vaginitis, suspected cervical dysplasia, and pregnancy.[3]

Emergency contraceptive form: The medication is not for use in women confirmed to be pregnant; however, there is no proof nor reports of adverse effects on the mother or fetus following inadvertent exposure during pregnancy.[10]

Pregnancy for the IUD: Use during pregnancy or suspected pregnancy is contraindicated. 

Combined ethinylestradiol and levonorgestrel is pregnancy category X. 

Breastfeeding: levonorgestrel is present in breast milk; however, the relative infant dose is 8%. Breastfeeding is acceptable when the relative infant dose of a medication is less than 10%.[11]

Monitoring

Routine examinations with a gynecologist are encouraged for the long-term combined oral pill or intrauterine device birth control options to monitor side effects and possible pregnancy. Levonorgestrel undergoes metabolism by the liver and is subject to impairment in patients with liver dysfunction. Therefore, monitoring liver function tests at the time of administration may be beneficial. Also, drugs containing CYP3A4 cytochrome p450 liver-enzyme inducing properties require close vigilance when a patient takes levonorgestrel. Patients may need to consider another emergency contraceptive method to avoid drug-drug interactions. These liver-enzyme-inducing drugs can cause rapid metabolism and decrease the efficacy of levonorgestrel when there is concomitant use.[12]

Toxicity

There is a lack of research regarding the toxic levels and effects in humans. While there could be toxicity seen in patients with liver disease, there is not enough research to support this. More human trial studies will be necessary. There have been studies that show LD50 to be over 5000 mg/kg in rats when given orally, with a significant decrease in white blood cell counts.[13]

Enhancing Healthcare Team Outcomes

While levonorgestrel is a first-line emergency contraceptive for unwanted pregnancy, communication and teamwork between primary care physicians, gynecologists, obstetricians, pharmacists, nurse practitioners, physician assistants, and nursing staff working together in an interprofessional team approach to care can make a tangible difference in a patient’s experience while taking levonorgestrel. There has been controversy about the morning-after pill being available without a prescription and sold over the counter at any local pharmacy. This agent can be deemed a drug that promotes risky sexual behavior and can also be a drug of convenience for both perceived and verifiable contraceptive failures. This issue is how healthcare teams can combine patient education with adequate treatment plans to promote levonorgestrel use in the most effective way without compromising patient safety.[14] [Level 5]

• Primary care physicians and gynecologists should routinely ask the patient about pertinent sexual history to help monitor sexual behavior and document changes.
• Maintenance of a strong physician-patient relationship so that the patients trust the physicians and can be open and honest about their sexual practices and potentially risky behavior in a judgment-free atmosphere.
• Pharmacists should emphasize the side effects of levonorgestrel, its strict timeline to achieve optimal drug efficacy, and how it will not prevent sexually transmitted infections and diseases.

These examples of interprofessional strategies can optimize the benefits of therapy with levonorgestrel. [Level 5]