What is Anastrozole (Arimidex)?

Theanastrozole, also known by the brand name Arimidex, is a potent aromatase inhibitor of third generation, a highly selective, nonsteroidal drug. It was initially developed as an anticancer drug and is still widely used in the treatment of estrogen-dependent breast cancer. Clinical studies have demonstrated Arimidex’s high efficacy in reducing the growth of estrogen-sensitive tumors.

In addition to its use in oncology, anastrozole is also used in men. In men, Arimidex significantly reduces circulating estrogen levels, preventing the negative effects associated with hyperestrogenism. Excess estrogen can cause gynecomastia, water retention, and suppression of luteinizing hormone (LH) secretion, resulting in reduced endogenous testosterone production. By blocking aromatization, anastrozole helps maintain an optimal testosterone/estrogen ratio.

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Mechanism of action of Arimidex (Anastrozole)

Testosterone aromatization

In the human body, testosterone can be converted to estradiol through the action of the enzyme aromatase, which is present in adipose tissue, the liver, and the brain. This process, called flavoring, it is a natural process, but when it occurs in excess, it leads to high levels of estrogen.

Testosterone → (aromatase) → Estradiol

If this conversion is too pronounced, the risk of estrogenic side effects increases. This is where anastrozole comes into play.

Action of anastrozole

Arimidex works by blocking the aromatase enzyme and drastically reducing estrogen synthesis:

• Aromatase Inhibition: Anastrozole binds to the enzyme and inhibits its activity, preventing the conversion of testosterone to estradiol.

• Estrogen reduction: Circulating estradiol levels decrease significantly, promoting a more stable hormonal profile.

• Positive feedback effect: The decrease in estrogen reduces negative feedback on the hypothalamus and pituitary gland, increasing the secretion of LH and FSH. This stimulates the testes to produce more endogenous testosterone

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Importance of blood tests

The use of Arimidex requires constant monitoring. Blood tests help maintain hormonal balance and avoid both excess and hypersuppression of estrogen.

Recommended reference values for men:

• Estradiol: 10–40 pg/mL

• Total testosterone: 600–1,500 ng/dL

The frequency of testing depends on the type of steroids used (short- or long-acting esters), but generally ranges from 10–14 days one 3–4 weeks

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Dosage and adjustment

A dose of 1 mg of anastrozole It can reduce estradiol levels by as much as 80–90%.
A common approach involves:

• Starting dose: 0.5 mg of Arimidex every other day

• Adjustment Based on blood tests:

  • Estradiol > 40 pg/mL → increase dose

  • Estradiol < 10 pg/mL → reduce the frequency or discontinue

The dosage must always be personalized.

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Pharmacological profile

• Half-life: 40–50 hours

• Frequency of use: once every 1–5 days

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Main effects

• Prevention of gynecomastia

• Estrogen reduction

• Better muscle definition

• Support for the recovery of the hypothalamus-pituitary-testes axis

• Prevention of water retention and estrogen-dependent hypertension

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Possible side effects

• Joint pain

• Reduction in bone density

• Changes in lipid profile

• Decreased libido

• Depressed mood in cases of estrogen hypersuppression

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Storage

• Keep out of reach of children

• Store in a cool, dry place.

• At room temperature

• Do not use after the expiration date