Anastrozole prevents the conversion of adrenal androgens (e.g. testosterone) to estrogen in peripheral and tumour tissues. As the growth of many breast cancers is stimulated and/or maintained by the presence of estrogen, anastrozole helps to treat these cancers by decreasing the levels of circulating estrogens. Anastrozole has a relatively long duration of action allowing for once daily dosing – serum estradiol is reduced by approximately 70% within 24 hours of beginning therapy with 1mg once daily, and levels remain suppressed for up to 6 days following cessation of therapy.
The incidence of ischemic cardiovascular events was increased during anastrozole therapy and patients with pre-existing ischemic heart disease should consider the risks and benefits of anastrozole before beginning therapy. Anastrozole has also been reported to decrease spine and hip bone mineral density (BMD), so consideration should be given to monitoring of BMD in patients receiving long-term therapy.
Anastrazole exerts its anti-estrogenic effects via selective and competitive inhibition of the aromatase enzyme found predominantly in the adrenal glands, liver, and fatty tissues. Many breast cancers are hormone receptor-positive, meaning their growth is stimulated and/or maintained by the presence of hormones such as estrogen or progesterone. In postmenopausal women, estrogen is primarily derived from the conversion of adrenally-produced androgens into estrogens by the aromatase enzyme – by competitively inhibiting the biosynthesis of estrogen at these enzymes, anastrozole effectively suppresses circulating estrogen levels and, subsequently, the growth of hormone receptor-positive tumours.
There is limited evidence for anastrozole’s effectiveness in men.
In one small study, anastrozole increased testosterone in older men with mild hypogonadism (low T) (Leder, 2004). In another study looking at men with low testosterone and infertility, taking anastrozole led to increased testosterone and increased sperm count in some (Shoshany, 2017).
Although anastrozole may increase testosterone levels, a recent analysis suggests that it doesn’t lead to improvements in sexual function like better erections or higher libido (sex drive). It also doesn’t improve semen quality. Currently, there isn’t sufficient evidence to recommend anastrozole as a routine treatment for low T in clinical practice (Awouter, 2020).
When compared to clomiphene, another off-label treatment for low T, men had significantly higher increases in testosterone than on anastrozole (Helo, 2015).
In some cases, a healthcare professional might consider prescribing low-dose anastrozole for men who receive TRT. The reason is that testosterone injections can increase estrogen levels, sometimes leading to unwanted breast growth (gynecomastia) in men. Arimidex and other aromatase inhibitors may reduce estrogen hormone levels in men and potentially treat gynecomastia (Rhoden, 2004).
How Does Anastrozole Work In Men?
We often think of testosterone and estrogen as exclusively male (androgen) and female (estrogen) hormones. However, men and women naturally produce both hormones, and a balance between the two is vital for good health in both sexes.
In men, having too little testosterone or too much estrogen can lead to problems like low sex drive, breast tenderness or enlargement, and erectile dysfunction. The primary sex hormone for men is testosterone, which is made in what are called Leydig cells in the testicles. Men also make a small amount of estradiol, a potent estrogen (de Ronde, 2011).
Estradiol is made directly by the testicles, but the majority comes from the conversion of testosterone into estradiol by the aromatase enzyme. Anastrozole blocks the action of aromatase (called aromatization), which slows down the conversion of testosterone to estradiol. This boosts overall testosterone levels and lowers estradiol (de Ronde, 2011).
Side Effects Of Anastrozole
Most of what we know about the side effects of anastrozole comes from research in women who took it as a cancer treatment. Side effects reported included hot flashes, back pain, arthritis, depression, and bone fractures (FDA, 2011).
One possible side effect of anastrozole in men is decreased bone health, which is another reason why the drug is not recommended as a routine treatment for low T. In older men with low testosterone, a study showed that anastrozole treatment improved T levels, but also decreased spinal bone density (Burnett-Bowie, 2009).
What Is Low Testosterone?
Low T (hypogonadism) affects an estimated 40% of men over 45. Having low testosterone can contribute to bothersome symptoms like erectile dysfunction, low libido, decreased muscle strength, and loss of bone mass (osteoporosis) (Sizar, 2021).
Age is the most common cause of low T. However, other factors that play a role include obesity, sleep apnea, certain medications, and viral infections (Sizar, 2021).
If you think you have a testosterone deficiency, a healthcare provider can perform a blood test to find out for sure. Typically, they’ll order tests to check your total testosterone and free testosterone levels, preferably in the morning (Sizar, 2021).
As we mentioned, a common low T treatment is testosterone replacement therapy. TRT comes in several forms including injections, gels, and patches. TRT works by giving your body exogenous testosterone to raise your baseline hormone levels; when taken as directed, testosterone therapy is safe and effective (Rivas, 2014).
The downside is there are side effects of testosterone therapy, the major one being its negative impact on male fertility. Over time, TRT shuts down your body’s natural sperm and testosterone production, which can eventually lead to infertility (Patel, 2019).
What Should I Know About Storage And Disposal Of This Medication?
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).
It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA’s Safe Disposal of Medicines website for more information if you do not have access to a take-back program.
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of anastrozole in children. However, efficacy has not been established to treat teenage boys with pubertal gynecomastia and to treat precocious puberty in teenage girls with McCune-Albright Syndrome.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of anastrozole in the elderly.
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.
Other Medical Problems
The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:
- Bone problems (eg, osteoporosis) or
- Hypercholesterolemia (high cholesterol or fat in the blood) or
- Ischemic heart disease (eg, heart attack, angina), history of, or
- Liver disease—Use with caution. May make these conditions worse.
- Premenopausal women (still having menstrual cycles)—Should not be used in these patients.
Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. To do so may increase the chance for side effects.
This medicine comes with a patient information leaflet. Read and follow these instructions carefully. Ask your doctor if you have any questions.
You may take this medicine with or without food.
Anastrozole sometimes causes nausea, vomiting, or diarrhea. However, it is very important that you continue to use the medicine, even if you begin to feel ill. Ask your doctor for ways to prevent these effects or make them less severe.
The dose of this medicine will be different for different patients. Follow your doctor’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.