Fulvestrant is an estrogen receptor antagonist, primarily indicated for the treatment of hormone receptor‑positive, human epidermal growth factor receptor 2 (HER2)‑negative advanced breast cancer.

1. Dosage and Administration of Fulvestrant

1.1 Standard Dosing Regimen

The recommended dose of fulvestrant is 500 mg, administered via intramuscular (IM) injectionDailyMed.

Following the initial dose, additional injections are required on Day 15 and Day 29, with subsequent maintenance injections administered once monthly.

Each administration consists of two 5‑mL injections, delivered into the gluteal muscles of both buttocks. Each injection should be administered slowly, over approximately 1–2 minutesDailyMed.

1.2 Dosage Adjustment in Special Populations

For patients with moderate hepatic impairment (Child‑Pugh Class B), the recommended dose is reduced to 250 mg.

In this case, only one 5‑mL injection is administered, while the dosing schedule remains unchanged (Day 1, Day 15, Day 29, then once monthly).

Fulvestrant is not recommended for use in patients with severe hepatic impairment.

2. Precautions for Fulvestrant Use

2.1 Bleeding Risk Prevention

Due to the intramuscular route of administration, extreme caution is advised in patients with a bleeding diathesis, thrombocytopenia, or those receiving anticoagulant therapy (e.g., warfarin).

These patients must inform their healthcare provider of their condition prior to injection to allow for risk assessment and implementation of necessary precautions.

2.2 Injection Site‑Related Precautions

Fulvestrant is injected into the gluteal muscle, which is in close proximity to the sciatic nerve; therefore, special care must be taken during administration.

If symptoms such as leg numbness, tingling, or weakness occur post‑injection, medical personnel should be contacted immediately, as these may indicate nerve injury.

2.3 Hepatic Function Monitoring

Fulvestrant is primarily metabolized in the liver, and elevations in liver enzymes may occur during treatment.

In clinical studies, more than 15% of patients experienced elevations in ALT, AST, or alkaline phosphatase, with 1–2% of these being Grade 3–4 elevations.

Therefore, regular monitoring of hepatic function is recommended throughout the treatment course.

2.4 Fetal Risk

Fulvestrant may cause harm to the fetus.

Women of childbearing potential must use effective contraception during treatment and for 1 year following the last dose.

If pregnancy is suspected or confirmed, the healthcare provider must be notified immediately.

2.5 Interference with Estrogen Assays

Due to its structural similarity to estradiol, fulvestrant may interfere with immunoassay‑based estrogen testing, potentially leading to falsely elevated results.

This must be taken into consideration when monitoring estrogen levels.

3. Patient Health and Lifestyle Management

3.1 Management of Common Adverse Reactions

Common adverse reactions during fulvestrant therapy may include injection site pain, nausea, bone pain, arthralgia, headache, back pain, and fatigue. Patients may employ the following measures to alleviate discomfort:

Apply a cold compress to the injection site post‑administration to reduce pain and discomfort.

For nausea, try small, frequent meals and avoid greasy or fatty foods.

For bone and joint pain, use appropriate analgesics under the guidance of a physician.

3.2 Daily Lifestyle Adjustments

During treatment, patients should ensure adequate rest and avoid excessive physical exertion.

When experiencing fatigue and weakness, adjust activity levels accordingly and ensure sufficient sleep.

Maintain moderate physical activity to preserve muscle strength and joint flexibility, but avoid strenuous exercise.