Dienogest

MECHANISM OF ACTION

Dienogest is a synthetic progestin that binds to progesterone receptors in target tissues. It suppresses the proliferation of endometrial tissue by creating a progestogenic and hypoestrogenic environment, leading to atrophy of ectopic endometrial implants, which is particularly beneficial in the treatment of endometriosis.

PHARMACOKINETICS

Absorption

Dienogest is rapidly and almost completely absorbed after oral administration. It reaches peak plasma concentrations within approximately 1–2 hours. Food does not significantly affect its absorption, allowing flexible administration with or without meals.

Distribution

Dienogest has a moderate volume of distribution, approximately 30–40 L in adults, indicating that it distributes well into body tissues but is not extensively sequestered in fat. It binds moderately to plasma proteins, primarily albumin, which helps maintain systemic circulation while allowing tissue penetration.

Metabolism

Dienogest is extensively metabolized in the liver, primarily via cytochrome P450 enzymes (mainly CYP3A4). Its metabolism involves hydroxylation and conjugation, producing metabolites that are mostly inactive.

Elimination

Dienogest is primarily eliminated via the kidneys as metabolites, with only a small fraction excreted unchanged in the urine. The elimination half-life is approximately 9–10 hours, supporting once-daily dosing.

PHARMACODYNAMICS

Dienogest is a synthetic progestin that exerts its therapeutic effects by binding to progesterone receptors in target tissues. In endometriosis, it suppresses the proliferation of ectopic endometrial tissue by creating a progestogenic and hypoestrogenic environment, leading to atrophy of lesions and reduction of pain. It also inhibits ovulation by suppressing the luteinizing hormone surge when used in contraceptive formulations.

ADMINISTRATION

Dienogest is administered orally, usually in the form of tablets. For the treatment of endometriosis, the typical dose is 2 mg once daily, while in combined oral contraceptives, it is used in fixed-dose combinations with ethinylestradiol. The drug can be taken with or without food, as food does not significantly affect its absorption.

DOSAGE AND STRENGTH

For the treatment of endometriosis, dienogest is typically administered as 2 mg orally once daily, often continued for 6 to 12 months depending on clinical response. When used in contraceptive formulations, it is combined with ethinylestradiol (usually 30 µg) in a fixed-dose tablet taken once daily according to the standard contraceptive regimen.

DRUG INTERACTIONS

Dienogest is primarily metabolized by CYP3A4, so drugs that induce or inhibit this enzyme can affect its plasma levels. CYP3A4 inducers, such as rifampicin, phenytoin, carbamazepine, or St. John’s Wort, may reduce dienogest efficacy, potentially decreasing contraceptive or endometriosis control. CYP3A4 inhibitors, including ketoconazole, itraconazole, or ritonavir, can increase dienogest levels, possibly enhancing side effects.

FOOD INTERACTIONS

Dienogest is primarily metabolized by CYP3A4, so drugs that induce or inhibit this enzyme can affect its plasma levels. CYP3A4 inducers, such as rifampicin, phenytoin, carbamazepine, or St. John’s Wort, may reduce dienogest efficacy, potentially decreasing contraceptive or endometriosis control.

CONTRAINDICATIONS

Dienogest is contraindicated in individuals with a known hypersensitivity to the drug or any of its components, as well as in those with active or a history of thromboembolic disorders, severe liver disease, or undiagnosed abnormal uterine bleeding.

SIDE EFFECTS

• Headache  

• Breast tenderness 

• Nausea and vomiting 

• Abdominal pain 

• Irregular menstrual bleeding or spotting 

• Mood changes or depression 

• Weight gain 

• Acne or oily skin (rare) 

• Thromboembolic events (rare, mainly in high-risk patients) 

• Liver function abnormalities (rare) 

• Fatigue  

• Dizziness.

OVER DOSAGE 

Overdose of dienogest is uncommon, and there is limited evidence of serious toxicity. Reported symptoms may include nausea, vomiting, abdominal pain, fatigue, and breast tenderness. Management is primarily supportive and symptomatic, as there is no specific antidote.

TOXICITY

Dienogest is generally well tolerated, and serious toxicity is rare. The most commonly reported adverse effects relate to its hormonal activity, including menstrual irregularities, breast tenderness, headache, and nausea. Severe toxic effects such as thromboembolic events, liver dysfunction, or mood disturbances are uncommon but may occur, particularly in patients with predisposing risk factors. Long-term use requires monitoring for changes in liver function, blood pressure, and overall hormonal balance.