Ethinyl Estradiol And Levonorgestrel (Transdermal)

Introduction Overview

Generic Name

ethinyl estradiol and levonorgestrel (transdermal)

Brand Name

Twirla

Dosage Form

Transdermal patch

Drug Class

Contraceptives

Pharmacokinetics

Absorption:
Twirla delivers ethinyl estradiol and levonorgestrel via a transdermal patch system which allows the drugs to be steadily absorbed through the skin into the systemic circulation. Upon application to clean, dry, intact skin, the patch releases a continuous, controlled amount of hormones over a 7-day period. This route avoids first-pass hepatic metabolism associated with oral administration, resulting in more consistent and prolonged plasma drug levels. Clinical pharmacokinetic studies demonstrate steady state concentrations within several dosing cycles, optimizing contraceptive efficacy.

Distribution:
After absorption, ethinyl estradiol and levonorgestrel are extensively bound to plasma proteins, primarily sex hormone-binding globulin (SHBG) and albumin. Levonorgestrel exhibits a high affinity for SHBG, which influences its distribution volume. Both hormones distribute throughout body tissues, with lipophilicity assisting transmembrane passage. Distribution is affected by patient factors such as body mass index (BMI); notably, efficacy decreases in women with BMI ≥ 25 kg/m², likely due to altered pharmacokinetics and increased volume of distribution.

Metabolism:
Ethinyl estradiol undergoes extensive hepatic metabolism mainly via cytochrome P450 enzymes, including CYP3A4, through oxidative and conjugative pathways. Levonorgestrel is also metabolized hepatically via reduction, hydroxylation, and conjugation reactions catalyzed by hepatic enzymes. The transdermal route leads to lower peak hepatic exposure but metabolism is otherwise typical for these steroids, resulting in various inactive metabolites excreted primarily in urine and bile.

Elimination:
The elimination half-life for ethinyl estradiol delivered transdermally is approximately 20–30 hours, whereas levonorgestrel’s half-life ranges from 24 to 32 hours. Both hormones and their metabolites are eliminated via renal and fecal routes. Steady application of the patch maintains therapeutic plasma levels, and hormone levels decline gradually after patch removal. Pharmacokinetic parameters indicate no accumulation beyond steady state with standard weekly patch changes, ensuring consistent contraceptive protection.

Dosage Forms

Available Dosage Forms:
Twirla is available exclusively as a transdermal contraceptive patch designed for weekly application.

Dosages for Adults and Adolescents:
The standard dosing regimen for Twirla is one patch applied once weekly for three consecutive weeks (21 days), followed by a patch-free interval of 7 days to allow for withdrawal bleeding. The cycle then repeats every 28 days. Each patch provides a continuous systemic delivery of ethinyl estradiol and levonorgestrel sufficient for effective contraception.

Specific Patient Populations:
Twirla is indicated for use in women with a body mass index (BMI) less than 30 kg/m², with clinical evidence showing reduced contraceptive effectiveness in women with BMI between 25 and 30 kg/m². Use is contraindicated or not recommended in patients with uncontrolled hypertension, cardiovascular disease, hepatic impairment, or those who smoke and are over 35 years old due to increased risk of thromboembolic events. The patch is not advised during pregnancy or breastfeeding due to hormonal effects on milk production.

Patch Application Instructions:
The patch should be applied to clean, dry, intact skin on areas such as the buttocks, abdomen, upper outer arm, or upper torso, avoiding breasts and areas subject to friction from tight clothing. The patch must not be cut or layered. Storage conditions recommend keeping patches in their foil pouches at room temperature away from moisture and heat.

Mechanism Of Action

Twirla’s contraceptive effectiveness arises from the combined actions of its two active components: ethinyl estradiol, a synthetic estrogen, and levonorgestrel, a potent synthetic progestin. Primarily, these hormones prevent ovulation by suppressing the hypothalamic-pituitary-ovarian axis. Ethinyl estradiol inhibits the release of follicle-stimulating hormone (FSH), reducing follicular development, while levonorgestrel suppresses the luteinizing hormone (LH) surge, thus preventing the release of an ovum.

Additionally, levonorgestrel induces changes in the cervical mucus, rendering it thick and hostile to sperm penetration, thereby decreasing fertilization likelihood. The hormones also alter the endometrial lining, making it less receptive for implantation should fertilization occur. This multi-pronged mechanism ensures highly effective pregnancy prevention.

At the cellular level, these hormones bind intracellular estrogen and progesterone receptors, modulating gene transcription patterns critical for reproductive tissue function. Ethinyl estradiol's structural modification allows high oral bioavailability and receptor affinity, while levonorgestrel exhibits strong progestogenic effects with minimal androgenic activity.

Comparatively, Twirla’s transdermal delivery bypasses hepatic first-pass metabolism seen in oral contraceptives, affording steadier hormone plasma levels and potentially reducing some estrogen-related side effects. Clinical studies demonstrate its contraceptive efficacy is on par with oral combination contraceptives when used according to prescribed regimens, though efficacy may be compromised in overweight individuals due to altered pharmacokinetics.

Pharmacological Actions

Inhibits ovulation through suppression of hypothalamic-pituitary-ovarian axis hormonal secretion.
Thickens cervical mucus to impede sperm transport and fertilization.
Induces endometrial changes unfavorable to implantation of a fertilized egg.
Exerts estrogenic effects maintaining hormonal balance and reproductive tissue function.
Displays progestogenic activity modulating gene expression via progesterone receptor binding.
Prevents pregnancy by a multi-mechanistic approach combining estrogen and progestin actions.
Maintains steady systemic hormone levels via transdermal delivery, reducing peak plasma fluctuations.
Reduces menstrual bleeding and dysmenorrhea associated with hormonal contraceptive use.

Therapeutic Or Clinical Uses

Primary prevention of pregnancy in women capable of becoming pregnant.
Alternative contraceptive method for women preferring non-oral delivery systems.
Suitable for women desiring weekly dosing rather than daily oral contraceptive pills.
Option for contraception in women without contraindications such as high BMI or thromboembolic risk.
Management of contraceptive needs in women with compliant adherence to weekly patch changes.
Provides predictable menstrual cycles with regular withdrawal bleeding during patch-free week.
May be used in patients with challenges swallowing oral contraceptive formulations.

Side Or Adverse Effects

Menstrual cramps and pelvic discomfort.
Nausea, often mild and transient at therapy initiation.
Weight gain associated with fluid retention or metabolic changes.
Headaches, including migraine exacerbation in some users.
Localized skin reactions at patch application site such as itching, redness, rash, swelling, or dryness.
Increased risk of serious cardiovascular events including blood clots, stroke, and heart attack, particularly in smokers over 35 years.
Change in mood or symptoms of depression.
Breakthrough vaginal bleeding or spotting, especially during the first three months.
Jaundice or liver function disturbances.
Swelling in extremities due to fluid retention or thrombotic events.
Potential for serious allergic reactions including hives and breathing difficulty.
Potential for elevated blood pressure in susceptible individuals.
Altered lipid metabolism contributing to hyperlipidemia risks.
In rare cases, vision changes or severe headaches signaling neurological complications.

Precautions

Contraindicated in women with a BMI ≥30 kg/m² due to reduced contraceptive efficacy and higher thrombotic risk.
Avoid use in patients with uncontrolled hypertension or cardiovascular diseases.
Monitor and control high blood pressure prior to initiation and during therapy.
Use caution in diabetic patients, especially with vascular complications or long-standing disease.
Not recommended for use in smokers over 35 years due to significantly increased cardiovascular risk.
Discontinue use several weeks before major surgery or prolonged immobilization to reduce thromboembolism risk.
Avoid application of skin products such as lotions or oils on the patch application site.
Patients with liver disease or history of hormone-related cancers should avoid Twirla.
Use backup contraception when starting therapy or if the patch is lost or detached for more than 24 hours.
Evaluate for signs of depression and mood changes during use.
Protect exposed skin from excessive sun exposure to prevent chloasma; consider sunscreen use.
Not to be used in pregnancy or during breastfeeding due to hormonal effects on milk production.
Regular follow-up and blood pressure monitoring are recommended.
Advise patients regarding proper patch application and disposal to prevent accidental exposure.
Be aware of potential drug interactions that may reduce contraceptive effectiveness.

Warnings

Do not use Twirla if you have uncontrolled hypertension, heart disease, or history of blood clots.
Use increases risk of serious cardiovascular events including stroke, myocardial infarction, and venous thromboembolism.
Smoking significantly increases cardiovascular risk; Twirla is contraindicated in smokers over age 35.
Discontinue if severe migraine headaches with aura develop or worsen.
Avoid use in presence of active liver disease or liver tumors.
Hepatitis C medications containing ombitasvir/paritaprevir/ritonavir can interact adversely; avoid concurrent use.
Do not use during pregnancy; may cause fetal harm if administered.
Monitor for signs of thromboembolic events such as sudden vision loss, limb swelling, or chest pain.
Patch should not be applied to broken, irritated, or damaged skin.
Missed doses or prolonged patch-free intervals increase risk of unintended pregnancy.
Fold and dispose used patches carefully to prevent unintentional exposure to hormones by children or pets.
The patch may cause skin irritation at the application site; discontinue if severe rash or allergy occurs.
Potential for increased blood pressure; baseline and periodic monitoring advised.
Do not wear more than one patch simultaneously.
Avoid prolonged patch-free intervals beyond seven days to maintain contraceptive protection.

Contraindication

Uncontrolled high blood pressure.
Active heart disease including coronary artery disease.
History of stroke or myocardial infarction.
Known thrombophlebitis or thromboembolic disorders, including hereditary clotting abnormalities.
Severe liver disease or liver tumors (benign or malignant).
Hormone-sensitive cancers including breast, uterine, cervical, or vaginal cancer.
Undiagnosed abnormal vaginal bleeding.
Severe migraine headaches, especially with focal neurological symptoms.
Use of concomitant hepatitis C therapy with regimens containing ombitasvir, paritaprevir, and ritonavir.
Women who smoke and are older than 35 years of age.
Pregnancy or suspicion of pregnancy.
Breastfeeding women due to potential impairment of lactation.
Known hypersensitivity to ethinyl estradiol, levonorgestrel, or any patch component.
Previous history of estrogen- or progestin-induced cholestasis or jaundice.
Active or recent (within 6 months) arterial or venous thromboembolism.

Drug Interactions

Rifampin and rifabutin can decrease contraceptive hormone levels, reducing Twirla’s effectiveness.
Antifungals such as ketoconazole, itraconazole, and voriconazole may alter hormone metabolism.
Antiretrovirals including ritonavir, efavirenz, nevirapine, and other HIV protease inhibitors can impact hormone clearance.
Antibiotics like griseofulvin and certain broad-spectrum antibiotics could potentially decrease hormone efficacy.
Anti-epileptic drugs including carbamazepine, phenytoin, phenobarbital, oxcarbazepine, lamotrigine, topiramate, and felbamate may induce hepatic enzymes and reduce hormone levels.
St. John's Wort, a herbal supplement, induces metabolism of contraceptive steroids, decreasing efficacy.
Atorvastatin and rosuvastatin may have altered plasma concentrations when combined with hormonal contraceptives.
Aprepitant and acetaminophen have potential interactions impacting the metabolism of ethinyl estradiol and levonorgestrel.
Vitamin C (ascorbic acid) and bosentan may influence drug interactions though clinical relevance is limited.
Levothyroxine levels may require monitoring as hormonal contraception can affect thyroid hormone binding.
Concomitant use with other hormonal medications requires evaluation for additive effects.
Grapefruit products are to be avoided due to interference with cytochrome P450 enzymes affecting hormone levels.
Drugs that induce or inhibit cytochrome P450 enzymes can impact pharmacokinetics and efficacy.
Close monitoring is recommended when initiating or discontinuing interacting medications.
Use alternative or backup contraception when taking interacting drugs known to reduce hormonal contraceptive efficacy.

Preparations Of The Drug

Twirla transdermal contraceptive patch containing ethinyl estradiol and levonorgestrel designed for weekly application.
Each patch delivers a controlled dose of hormones through skin absorption over a 7-day period.
Patches are individually sealed in foil pouches to preserve drug stability and prevent contamination.
Patches should be stored at room temperature, protected from moisture and heat, and not frozen or refrigerated.
The medication is supplied with patient instructions emphasizing proper application, wear-time, and disposal.
Boxes typically contain multiple patches for a standard 3-week treatment cycle plus instructions for the patch-free interval.
Manufactured to conform with regulatory standards for transdermal drug delivery systems for contraceptive use.
Patches have a hypoallergenic adhesive surface to reduce skin irritation while ensuring secure adherence.
Each patch is designed to prevent cutting or alteration to ensure consistent dosing.
Provided in sizes and formulations approved by FDA with supporting clinical and safety data.
Accompanied by informational leaflets detailing warnings, precautions, and potential side effects.
Available only by prescription with medical supervision recommended for initiation and monitoring.
Disposable biohazard guidelines instruct folding patch with adhesive inside prior to disposal to prevent hormone exposure.
Packaging includes expiration date and lot number for quality control and traceability.
Patient support material is available to facilitate adherence and education on contraceptive efficacy.