|Trade names||Faslodex, others|
|Other names||ICI-182780; ZD-182780; ZD-9238; 7α-[9-[(4,4,5,5,5-Pentafluoropentyl)-sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17β-diol|
|Main uses||Breast cancer|
|Side effects||Nausea, diarrhea, headache, pain, hot flushes, cough, swelling, rash, trouble sleeping|
|Typical dose||500 mg|
|Metabolism||Hydroxylation, conjugation (glucuronidation, sulfation)|
|Elimination half-life||IM: 40–50 days|
|Chemical and physical data|
|Molar mass||606.78 g·mol−1|
|3D model (JSmol)|
|(what is this?)|
Fulvestrant, sold under the brand name Faslodex among others, is a medication used to treat breast cancer. Specifically it is used for hormone receptor (HR) positive cases. It is given by injection into a muscle.
Common side effects include nausea, diarrhea, headache, pain, hot flushes, cough, swelling, rash, and trouble sleeping. Other side effects may include low white blood cells, low red blood cells, low platelets, infection, and liver problems. It should not be used in pregnancy or breastfeeding. It is a selective estrogen receptor degrader (SERD) which binds to estrogen receptor resulting in their destruction.
Fulvestrant was approved for medical use in the United States in 2002 and Europe in 2004. It is available as a generic medication. In the United Kingdom it costs the NHS about £520 per dose of 2021. This amount in the United States costs about 100 USD.
Fulvestrant is used for the treatment of hormone receptor positive metastatic breast cancer or locally advanced unresectable disease in postmenopausal women; it is given by injection. A 2017 Cochrane review found it is as safe and effective as first line or second line endocrine therapy.
It is also used to treat ER-positive, HER2-negative advanced or metastatic breast cancer in combination with palbociclib in women with disease progression after first-line endocrine therapy. Due to the medication's having a chemical structure similar to that of estrogen, it can interact with immunoassays for blood estradiol concentrations and show falsely elevated results. This can improperly lead to discontinuing the treatment.
For breast cancer it is generally given at a dose of 500 mg every two weeks for three doses, and than 500 mg a month.
Very common (occurring in more than 10% of people) adverse effects include nausea, injection site reactions, weakness, and elevated transaminases. Common (between 1% and 10%) adverse effects include urinary tract infections, hypersensitivity reactions, loss of appetite, headache, blood clots in veins, hot flushes, vomiting, diarrhea, elevated bilirubin, rashes, and back pain. In a large clinical trial, the incidence of venous thromboembolism (VTE) with fulvestrant was 0.9%.
Fulvestrant is an antiestrogen which acts as an antagonist of the estrogen receptor (ER) and additionally as a selective estrogen receptor degrader (SERD). It works by binding to the estrogen receptor and making it more hydrophobic, which makes the receptor unstable and misfold, which in turn leads normal processes inside the cell to degrade it.
In addition to its antiestrogenic activity, fulvestrant is an agonist of the G protein-coupled estrogen receptor (GPER), albeit with relatively low affinity (10–100 nM, relative to 3–6 nM for estradiol).
Fulvestrant after an intramuscular injection is slowly absorbed and maximal levels (Cmax) are reached after 5 days on average with a range of 2 to 19 days. The elimination half-life of fulvestrant with intramuscular injection is 40 to 50 days. This is 40 times longer than the half-life of fulvestrant by intravenous injection, indicating that its long half-life with intramuscular injection is due to slow absorption from the injection site. Levels of fulvestrant with 500 mg/month by intramuscular injection (and a single additional 500 mg loading dose on day 15 of therapy) in postmenopausal women with advanced breast cancer were 25.1 ng/mL (25,100 pg/mL) at peak and 28.0 ng/mL (28,000 pg/mL) at trough with a single dose and 28.0 ng/mL (28,000 pg/mL) at peak and 12.2 ng/mL (12,200 pg/mL) at trough after multiple doses at steady state.
Fulvestrant does not cross the blood–brain barrier in animals and may not in humans as well. Accordingly, no effects of fulvestrant on brain function have been observed in preclinical or clinical research. Fulvestrant is highly (99%) bound to plasma proteins. It is bound to very low density lipoprotein, low density lipoprotein, and high density lipoprotein, but not to sex hormone-binding globulin.
Fulvestrant appears to be metabolized along similar pathways as endogenous steroids; CYP3A4 may be involved, but non-cytochrome P450 routes appear to be more important. It does not inhibit any cytochrome P450 enzymes. Elimination is almost all via feces.
Fulvestrant, also known as 7α-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estradiol, is a synthetic estrane steroid and a derivative of estradiol. An alkyl-sulfinyl moiety was added to the endogenous estrogen receptor ligand.
Society and culture
The U.K. National Institute for Health and Clinical Excellence (NICE) said in 2011 that it found no evidence Faslodex was significantly better than existing treatments, so its widespread use would not be a good use of resources for the country's National Health Service. The first month's treatment of Faslodex, which starts with a loading dose, costs £1,044.82 ($1,666), and subsequent treatments cost £522.41 a month. In the 12 months ending June 2015, the UK price (excluding VAT) of a month's supply of anastrozole (Arimidex), which is off patent, cost 89 pence/day, and letrozole (Femara) cost £1.40/day.
The original patent for Faslodex expired in October 2004. Drugs subject to pre-marketing regulatory review are eligible for patent extension, and for this reason AstraZeneca got an extension of the patent to December 2011. AstraZeneca has filed later patents. A generic version of Faslodex has been approved by the FDA. However, this does not mean that the product will necessarily be commercially available - possibly because of drug patents and/or drug exclusivity. A later patent for Faslodex expires in January 2021. Atossa Genetics has a patent for the administration of fulvestrant into the breast via a microcatheter invented by Susan Love.
Because fulvestrant cannot be given orally, efforts have been made to develop SERD drugs that can be taken by mouth, including brilanestrant and elacestrant. The clinical success of fulvestrant also led to efforts to discover and develop a parallel drug class of selective androgen receptor degraders (SARDs).
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