Introduction: Letrozole is a new generation, highly selective aromatase inhibitor, a synthetically derived benzotriazole. By inhibiting aromatase, it lowers estrogen levels, eliminating estrogen's stimulating effect on tumor growth. Its in vivo activity is 150-250 times stronger than the first-generation aromatase inhibitor aminoglutethimide. Due to its high selectivity, it does not affect glucocorticoids, mineralocorticoids, or thyroid function. High-dose use does not inhibit the secretion of adrenal corticosteroids, resulting in a high therapeutic index.
Letrozole is mainly used for postmenopausal women with estrogen receptor (ER/PR-positive) positive breast cancer. Breast cancer is estrogen-related. In premenopausal women, estrogen primarily comes from the ovaries, while in postmenopausal women, it is mainly converted from androgens to estrogen. Letrozole inhibits this conversion by suppressing aromatase, thus reducing estrogen levels. In simple terms, Letrozole is a "gatekeeper" drug that inhibits the conversion of estrogen in postmenopausal women.
Mechanism of Action: Letrozole competitively binds to the heme of the subunit of cytochrome P450 enzymes, inhibiting aromatase and reducing estrogen biosynthesis in all tissues. Tumors lack the nutrient 'estrogen', thereby reducing the risk of metastasis and recurrence.
Indications: Preclinical studies show that Letrozole has no potential toxicity to various systems and target organs, no mutagenic or carcinogenic effects, minimal toxic side effects, good tolerance, and a stronger anti-tumor effect compared to other aromatase inhibitors and anti-estrogen drugs. It is suitable for treating late-stage breast cancer in postmenopausal patients for whom anti-estrogen therapy has failed and for early-stage breast cancer treatment.
Differences from Anastrozole: Letrozole tablets are suitable for late-stage postmenopausal breast cancer, often used as second-line treatment after the failure of anti-estrogen therapy. Anastrozole is a potent selective triazole aromatase inhibitor that inhibits aromatase dependent on cytochrome P-450, blocking the biosynthesis of estrogen.
Adverse reactions and side effects from randomized controlled trials show that the incidence of adverse reactions possibly related to Letrozole, when taken orally at 2.5 mg per day, is 33%, significantly lower than the 46% in the Anastrozole group. Letrozole's adverse reactions are mostly mild to moderate, mainly manifesting as nausea (2%-9%), headache (0%-7%), bone pain (4%-10%), hot flashes (0%-9%), and weight gain (2%-8%). Other less common reactions include constipation, diarrhea, itching, rash, joint pain, chest pain, abdominal pain, fatigue, insomnia, dizziness, swelling, hypertension, arrhythmia, thrombosis, difficulty breathing, and vaginal bleeding. While most patients tolerate Letrozole well, it is important to note potential side effects, and Letrozole belongs to pregnancy category X. The FDA has not approved this drug for inducing ovulation, but evidence suggests it does not increase the risk of congenital malformations. It is recommended internationally as a first-line drug for inducing ovulation. Despite its half-life, administration during the early follicular phase results in clearance before fertilization. However, like all ovulation-inducing drugs, physicians must confirm non-pregnancy before starting treatment, typically through a blood pregnancy test. Chemical Properties: Melting point 181-183°C.
Uses: Pyrrole-type aromatase inhibitor.
Used in the treatment of breast cancer
Letrozole is a medication that is sometimes used for fertility treatment in women. It is primarily known as an aromatase inhibitor, commonly used in the treatment of breast cancer. However, in the context of fertility, letrozole is often prescribed to induce ovulation.
Here's how letrozole works for fertility:
Ovulation Induction: Letrozole stimulates the ovaries to produce more follicles, which are fluid-filled sacs containing eggs. This is important for women who have irregular or absent ovulation.
Estrogen Reduction: Letrozole reduces the levels of estrogen in the body. This reduction in estrogen levels leads to an increase in the release of follicle-stimulating hormone (FSH), which, in turn, stimulates the ovaries.
Increased Follicle Development: By influencing the hormonal environment, letrozole encourages the growth and development of ovarian follicles, increasing the chances of ovulation and pregnancy.
Improvement in Ovulation Quality: Letrozole can result in the development of a more dominant and healthier egg during the ovulation process.
It's important to note that letrozole is often used as an alternative to clomiphene citrate (Clomid) in certain cases, especially when Clomid has not been effective or well-tolerated.
Letrozole is a medication that is sometimes used for fertility treatment in women. It is primarily known as an aromatase inhibitor, commonly used in the treatment of breast cancer. However, in the context of fertility, letrozole is often prescribed to induce ovulation.
Here's how letrozole works for fertility:
Ovulation Induction: Letrozole stimulates the ovaries to produce more follicles, which are fluid-filled sacs containing eggs. This is important for women who have irregular or absent ovulation.
Estrogen Reduction: Letrozole reduces the levels of estrogen in the body. This reduction in estrogen levels leads to an increase in the release of follicle-stimulating hormone (FSH), which, in turn, stimulates the ovaries.
Increased Follicle Development: By influencing the hormonal environment, letrozole encourages the growth and development of ovarian follicles, increasing the chances of ovulation and pregnancy.
Improvement in Ovulation Quality: Letrozole can result in the development of a more dominant and healthier egg during the ovulation process.
It's important to note that letrozole is often used as an alternative to clomiphene citrate (Clomid) in certain cases, especially when Clomid has not been effective or well-tolerated.
If you are considering fertility treatment or have concerns about your fertility, it's crucial to consult with a healthcare professional who can assess your individual situation and provide personalized advice and guidance.
how many cycles of letrozole to get pregnant?
The number of cycles of letrozole required to achieve pregnancy can vary widely from one individual to another. It depends on various factors, including the underlying cause of infertility, the woman's age, overall health, and how her body responds to the medication.
In general, healthcare providers may prescribe a certain number of cycles of letrozole for ovulation induction, typically ranging from three to six cycles. During each cycle, the woman takes letrozole for a specific duration, and monitoring is often done through ultrasound and hormone level assessments to track follicle development and ovulation.
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