Antitumor agents, nonsteroidal competitive aromatase inhibitors. In postmenopausal women, estrogen is mainly formed by the enzyme aromatase, which converts androgens (mainly androstenedione and testosterone) synthesized by adrenals into estrone and estradiol. By inhibiting this enzyme, which is found in adipose tissue, liver and skeletal muscle, letrozole prevents the conversion of androgens to estrogen and promotes the regression of estrogen-dependent tumors. It reduces the concentration of estrogen in the systemic circulation by 75-95% without significantly affecting the synthesis of corticosteroids, aldosterone and thyroid hormones in the adrenal glands. After ingestion, it is rapidly and completely absorbed in the digestive tract. The rate of absorption does not depend on food intake.
Steady-state plasma concentrations are reached after 2-6 weeks of treatment. It does not accumulate in the body. About 60% of letrozole is bound to plasma proteins (mainly albumin). The concentration of letrozole in red blood cells is 80% of the plasma concentration. Letrozole is rapidly and widely distributed in tissues. At equilibrium, the apparent volume of distribution is 1.87 ± 0.47 l / kg.
In general, the side effects were mild or moderate and were mainly related to inhibition of estrogen synthesis.
The frequency of adverse reactions was very common (> 10%), common (1-10%), uncommon (0.1-1%), rare (0.01-0.1%), very rare (<0.01%). %), including individual reports). . .
From the digestive system: often – nausea, vomiting, indigestion, constipation, diarrhea; Sometimes – abdominal pain, stomatitis, dry mouth, increased activity of liver enzymes.
From the nervous system: often – headache, dizziness, depression; Uncommon – anxiety, irritability, irritability, drowsiness, insomnia, memory impairment, paraesthesia, paraesthesia, hypoaesthesia, taste disturbances, episodes of cerebrovascular events.
In some hematopoietic organs: sometimes – leukopenia.
Cardiovascular measurements: sometimes – palpitations, tachycardia, superficial and deep vein thrombophlebitis, increased blood pressure, coronary artery disease (angina, myocardial infarction, heart failure), thromboembolism; Rarely – pulmonary embolism, arterial thrombosis, stroke.
From the respiratory tract: sometimes – shortness of breath, cough.
Dermatological reactions: Common – alopecia, excessive sweating, rash (including erythema, maculopapular, bullous rash, psoriasis-like rash); Sometimes – itching, dry skin, hives; Very rare – angioedema, anaphylactic reaction.
From the musculoskeletal system: very often – arthralgia; Often – myalgia, bone pain, osteoporosis, fractures, sometimes – arthritis.
From the senses: sometimes – cataracts, eye irritation, visual disturbances, taste disturbances.
From the urinary system: sometimes – frequent urination, urinary tract infections.
From the reproductive system: sometimes – vaginal bleeding, vaginal bleeding, vaginal dryness, mammary gland pain.
Other: Very common – paroxysmal hot flushes (“hot flushes”); often – increased fatigue, asthenia, abuse, peripheral edema, weight gain, hypercholesterolaemia, loss of appetite, increased appetite; Sometimes – weight loss, thirst, high fever (fever), dry mucous membranes, swelling of the body, pain in the tumor lesion.
Special handling instructions Caution must be exercised when driving or operating potentially dangerous machinery and when performing other activities that require special attention.