Anastrozole

Drug Name

Anastrozole is often known by its brand name Arimidex.

Drug Class 

• Aromatase Inhibitor
• Antineoplastic Agent
• Endocrine-Metabolic Agent

Common Uses: What is Anastrozole Used For?

• Breast cancer, hormone receptor-positive or unknown
• DCIS (ductal carcinoma in situ)
• Male infertility with decreased testosterone level
• Ovarian cancer, estrogen or progesterone-receptor positive

Mechanism of Action: How Does Anastrozole Work?

Anastrozole is a potent and highly selective non-steroidal aromatase inhibitor.  Anastrozole is used for postmenopausal women with advanced breast cancer. It works by interfering with estradiol production in peripheral tissues, reducing circulating estradiol levels, which can be beneficial for women with breast cancer as many tumors are estrogen-stimulated.

Anastrozole inhibits the conversion of adrenally-generated androstenedione to estrone, the chief source of circulating estrogen in postmenopausal women. Despite its efficacy in suppressing estradiol levels by over 80%, anastrozole has shown no direct progestogenic, estrogenic, or androgenic activity. [2., 3., 4.]

Pharmacokinetics [1.]

Absorption

• Tmax, oral: 2 hours
• Bioavailability: 80%

Metabolism

• Liver: 85% via N-dealkylation, hydroxylation, and glucuronidation

Excretion

• Fecal: approximately 75%
• Renal: 10%

Elimination Half Life

• 50 hours

Common Side Effects of Anastrozole [2., 3., 4.]

What are the side effects of anastrozole? Is a common question.  Side effects of taking anastrozole may include hot flashes, physical weakness or lack of energy, joint pains, insomnia, depression, nausea, vomiting, rash, hypertension, osteoporosis, fractures, and swelling. 

Precautions: What Should Clinicians Know About the Side Effects of Anastrozole?

Cardiovascular:

• Monitoring of serum cholesterol levels is recommended due to reports of elevated levels; consider regular assessment.
• Patients with preexisting ischemic heart disease may face an increased risk of ischemic cardiovascular events; evaluate the risk versus benefit before initiating treatment.

Musculoskeletal:

• Regular monitoring for decreased bone mineral density is advised.

Reproductive:

• Females of reproductive potential should undergo pregnancy verification prior to treatment initiation and utilize effective contraception during and for at least 3 weeks after the last dose to prevent fetal harm.

Concomitant use:

• Avoid coadministration of tamoxifen and estrogen-containing therapies.

Clinical Considerations

Bone Mineral Density (BMD):

• Dual-energy X-ray absorptiometry (DXA) scans should be conducted at baseline and repeated every 1 to 2 years.

Osteoporosis and Fracture Risk:

• Evaluate osteoporosis and fracture risk in patients initiating therapy.

Cholesterol:

• Consider monitoring cholesterol levels during therapy.

Pregnancy Test:

• Verify the pregnancy status of females with reproductive potential before starting therapy.

X-ray of Thoracic and Lumbar Spine:

• Perform X-rays of the thoracic and lumbar spine to rule out vertebral fracture in patients with kyphosis, historical height loss of 6 cm or greater, acute incapacitating back pain syndrome, and those aged 65 years and older.

Foods to Avoid When Taking Anastrozole

There are no required foods to avoid when taking Anastrozole.  However, eating a healthy diet is important, especially when receiving treatment for cancer.  Focus on eating plenty of fruits, vegetables, lean proteins and healthy fats like olive oil, wild fish, nuts and seeds to reduce inflammation and promote cellular health.

High Levels of Anastrozole: Anastrozole Toxicity

High levels of Anastrozole in the body could mean that a person is taking more than the recommended dose of this medication.

Because this drug works by reducing the amount of estrogen in the body, excessive Anastrozole levels could potentially lead to an excessive reduction of estrogen, which could have other health implications.

Common symptoms of Anastrozole toxicity include nausea, vomiting, rash, hot flashes, headache, hypertension, vasodilation, peripheral edema, lymphedema, arthritis, arthralgia, back pain, asthenia, fatigue, depression, mood disturbances, cough, pharyngitis, and pain.  

Less common symptoms of Anastrozole toxicity may include chest pain, thromboembolic events (eg, pulmonary embolus, thrombophlebitis, and retinal vein thrombosis), pruritus, paresthesia, sweating, abdominal pain, diarrhea, dyspepsia, constipation, anorexia, dry mouth, urinary tract infection, vaginal bleeding, leukopenia, anemia, elevated liver enzymes, acute hepatitis, bone pain, myalgia, arthrosis, confusion, anxiety, nervousness, dizziness, dyspnea, sinusitis, bronchitis, and infection.

It's also possible that high levels of Anastrozole could be due to interactions with other medications, as some drugs can affect how it's metabolized and cleared from the body.

Individuals concerned about excessively high Anastrozole levels should discuss this with their prescribing doctor.  

Low Levels of Anastrozole

Treatment efficacy of Anastrozole is monitored according to changes in tumor growth and development.  

Concern of low levels of Anastrozole in the body could mean that the drug isn't being taken as prescribed or that the body isn't absorbing it properly, which could potentially allow the cancer cells to continue growing.

Dosing concerns should be discussed with the prescribing doctor.  

When Would I Take Anastrozole with Testosterone?

In some cases, men with low testosterone are over-converting their available testosterone to estrogen through the enzyme aromatase.  In this case, men given testosterone replacement therapy (TRT) may also be prescribed the drug anastrozole to reduce the conversion of testosterone to estrogen.