FULVESTRANT
Clinical safety rating: avoid
Contraindicated (not allowed)
Selective estrogen receptor downregulator (SERD). Binds to estrogen receptors (ER) with high affinity, downregulates ER expression, and inhibits estrogen-stimulated growth of breast cancer cells.
| Metabolism | Primarily metabolized via CYP3A4, with minor contributions from other pathways. The major route of elimination is via feces (approximately 90%) and urine (approximately 1%). |
| Excretion | Primarily hepatic metabolism via CYP3A4; <1% excreted renally as unchanged drug; ~90% eliminated in feces as metabolites, <1% in urine. |
| Half-life | Terminal elimination half-life ~40 days (range 30–50 days) due to slow release from intramuscular depot; achieves steady-state after ~3–6 months of monthly dosing. |
| Protein binding | 99% bound to plasma proteins, primarily albumin and to a lesser extent alpha-1-acid glycoprotein. |
| Volume of Distribution | 3–5 L/kg (approximately 210–350 L for a 70 kg adult), indicating extensive tissue distribution and binding to estrogen receptors. |
| Bioavailability | IM administration: ~100% (absolute bioavailability) due to complete absorption from the injection site; oral administration not bioavailable (<5%) due to extensive first-pass metabolism. |
| Onset of Action | IM administration: Clinical effects (estrogen receptor downregulation) detectable within 1–2 weeks; maximal antitumor response typically after 3–6 months. |
| Duration of Action | Duration of estrogen receptor suppression persists for ≥1 month after a single dose; clinical effects last as long as treatment continues (monthly dosing). |
| Molecular Weight | 606.77 |
500 mg intramuscularly on days 1, 15, 29, and then once monthly thereafter.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment (creatinine clearance 30-89 mL/min). Not studied in severe renal impairment (creatinine clearance <30 mL/min); use with caution. |
| Liver impairment | Mild hepatic impairment (Child-Pugh A): no dose adjustment. Moderate hepatic impairment (Child-Pugh B): 250 mg intramuscularly on days 1, 15, 29, and then once monthly. Severe hepatic impairment (Child-Pugh C): not recommended (no data). |
| Pediatric use | Not indicated; safety and efficacy not established in pediatric patients. |
| Geriatric use | No specific dose adjustment required; clinical studies included patients up to age 89 years with no overall differences in safety or efficacy compared to younger adults. |
| 1st trimester | Avoid. Fulvestrant is contraindicated during pregnancy due to estrogen receptor antagonism and potential for embryofetal harm based on animal studies. No human data available. |
| 2nd trimester | Avoid. Same risks as first trimester. Potential for fetal harm outweighs any benefit. |
| 3rd trimester | Avoid. Risk of fetal harm continues. Not recommended at any time during pregnancy. |
Clinical note
No significant drug interactions Can cause injection site reactions and nausea.
| Placental transfer | Animal studies indicate that fulvestrant crosses the placenta and can cause fetal toxicity. Human data are insufficient to quantify transfer, but based on molecular properties (MW 606.77) and high protein binding, limited transfer is expected; however, the risk of harm precludes use. |
| Breastfeeding | Due to its long half-life and potential for serious adverse effects in the nursing infant, breastfeeding is not recommended during fulvestrant therapy and for at least 1 month after the last dose. |
■ FDA Black Box Warning
None.
| Common Effects | Nausea |
| Serious Effects |
PregnancyHistory of hypersensitivity to fulvestrant or any excipientsSevere hepatic impairment (Child-Pugh Class C)
| Precautions | Injection site reactions (e.g., sciatica, neuralgia, neuropathy) may occur due to inadvertent injection near the sciatic nerve, Risk of bleeding in patients with thrombocytopenia or anticoagulant use, Potential for increased liver enzyme levels; monitor liver function, Fetal harm if administered to pregnant women; advise effective contraception |
| Food/Dietary | No known food interactions. Take with or without food. Avoid grapefruit and grapefruit juice as they may affect drug metabolism (minor CYP3A4 involvement). Maintain adequate calcium and vitamin D intake. |
Loading safety data…
| Lactation Rating | L5 (Contraindicated) |
| Teratogenic Risk | Fulvestrant is contraindicated in pregnancy. There are no adequate studies in pregnant women. Based on animal studies, fulvestrant can cause fetal harm when administered to a pregnant woman. In reproductive toxicity studies in rats and rabbits, fulvestrant caused embryofetal toxicity and teratogenicity at doses below the recommended human dose. First trimester: High risk of fetal malformations and pregnancy loss due to antiestrogenic effects. Second and third trimesters: Risk of fetal growth restriction and potential adverse effects on fetal reproductive tract development due to continued estrogen receptor blockade. |
| Fetal Monitoring | Pregnancy status must be verified prior to initiation of fulvestrant. Women of childbearing potential should use effective contraception during treatment and for at least 2 years after the last dose. If pregnancy occurs, immediate discontinuation is required. Monitor for fetal development via ultrasound if inadvertently exposed. No specific maternal monitoring beyond standard oncology care is indicated. |
| Fertility Effects | Fulvestrant may impair fertility in women of childbearing potential. In animal studies, fulvestrant disrupted estrous cycles and reduced fertility. Based on its mechanism of action (estrogen receptor downregulation), reversible disruption of ovarian function and menstrual cycles is expected. Long-term effects on fertility are unknown. |
| Clinical Pearls | Fulvestrant is a pure antiestrogen that downregulates estrogen receptors; it is not a SERM. Administer as intramuscular injection into the gluteal area slowly (1-2 minutes per injection). Two 5 mL injections (250 mg each) are given on days 1, 15, 29, then monthly. Monitor hepatic function and coagulation parameters. Use with caution in patients with bleeding disorders or thrombocytopenia. For postmenopausal women with hormone receptor-positive metastatic breast cancer, after prior antiestrogen therapy. Consider dose adjustment in moderate hepatic impairment (Child-Pugh class B): 250 mg on days 1, 15, 29, then monthly. |
| Patient Advice | This medication is given as an injection into the buttock muscle every two weeks for the first month, then once a month. · Common side effects include injection site pain, nausea, headache, and hot flashes. · Contact your healthcare provider if you experience unusual bleeding, bruising, or signs of liver problems (yellowing skin, dark urine). · Do not become pregnant while on this medication; use effective contraception if premenopausal. · Take calcium and vitamin D supplements as recommended for bone health. |