Ovestin (Estriol)

Estriol acts as a weak estrogen and is used primarily for conditions related to the urogenital tract in post‑menopausal women.

• Menopausal vaginal atrophy: restores vaginal epithelial thickness and reduces dryness.
• Postmenopausal urogenital symptoms: alleviates itching, burning, and discomfort during intercourse.
• Estrogen deficiency in the vagina: provides localized estrogen replacement to improve lubrication.
• Prevention of recurrent urinary tract infections: supports mucosal health that may lower infection risk.
• Adjunct to hormone replacement therapy: used when a low‑dose vaginal estrogen is preferred over systemic therapy.

• Estriol binds to estrogen receptors α and β in vaginal and urethral tissues, initiating transcription of genes that promote cellular proliferation, increased glycogen production, and enhanced blood flow. Its weaker affinity compared with estradiol results in predominantly local effects with limited systemic estrogenic activity, thereby restoring the normal vaginal microbiome and mucosal integrity. The localized action also modulates inflammatory mediators, contributing to symptom relief.

Estriol may cause a range of adverse reactions, which are generally categorized by frequency and severity.

Common Side Effects

• Vaginal irritation or discharge: mild irritation or watery discharge at the application site.
• Headache: transient mild to moderate headache.
• Breast tenderness: temporary soreness or swelling of breast tissue.
• Nausea: occasional mild nausea.

Serious or Rare Side Effects

• Endometrial hyperplasia: abnormal thickening of the uterine lining.
• Thromboembolic events: blood clots in veins or arteries.
• Severe allergic reaction: rash, swelling, or anaphylaxis.
• Unexplained vaginal bleeding: persistent or heavy bleeding.

When prescribing estriol, clinicians should consider several safety precautions to minimize risk.

• Pregnancy: avoid use because estrogen may affect fetal development.
• Breast cancer: contraindicated in active or past estrogen‑dependent breast malignancy.
• History of thromboembolism: use with caution and assess risk factors.
• Liver disease: monitor hepatic function as metabolism may be altered.
• Concomitant anticoagulant therapy: observe for increased bleeding tendency.
• Store at ambient temperature below 25°C: keep in the original pack, protect from moisture.

Estriol can interact with other medicines, influencing its effectiveness or safety.

Major Interactions (Avoid)

• Combined hormonal therapy: additive estrogen exposure may increase adverse events.
• Selective estrogen receptor modulators (e.g., tamoxifen): antagonistic actions can reduce therapeutic benefit.
• Anticoagulants (e.g., warfarin): may enhance bleeding risk.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole): may raise estriol plasma levels.
• CYP3A4 inducers (e.g., rifampin): may lower estriol effectiveness.
• Thyroid hormone replacement: estriol may alter thyroid hormone requirements.