What Are the Common Levothyroxine Side Effects?
Levothyroxine can be absorbed by the gastrointestinal tract, but the absorption is incomplete and the absorption rate is uncertain, especially when taken with food. After T4 is absorbed into the blood, most of it binds to plasma proteins, only about 0.03% exists in free form, about 80% binds to thyroxine-binding globulin, and a small amount binds to thyroxine-binding protein or albumin.
- Drug Name
- Levothyroxine
- Alias
- Thyroxine, levothyroxine, euthyroxine, levothyroxine sodium
- Main indications
- Cretinism and other hypothyroidism
- Dosage
- 0.1 to 0.2 mg orally each time, 3 times a day
- Levothyroxine can be absorbed by the gastrointestinal tract, but the absorption is incomplete and the absorption rate is uncertain, especially when taken with food. After T4 is absorbed into the blood, most of it binds to plasma proteins, only about 0.03% exists in free form, about 80% binds to thyroxine-binding globulin, and a small amount binds to thyroxine-binding protein or albumin.
Introduction to levothyroxine compounds
- Levothyroxine sodium is the sodium salt of levothyroxine. Levothyroxine, also called synthetic T4 or '3,5,3', 5'-tetraiodo-L-thyroxine is a synthetic form of thyroxine (thyroid hormone), used in patients with thyroid disorders Hormone replacement therapy. The natural thyroid hormone is, as in the pharmaceutical formulation, chemically chiral-L-configuration. D-thyroxine has been studied as an anti-cholesterol drug. But it was cancelled because of side effects on the heart.
Levothyroxine Basic Information
- Chinese name: thyroid hormone
- Chinese alias: 3,3 ', 5,5' '-tetraiodo-L-thyronine; 3,5,3', 5'-tetraiodothyronine; thyroxine and levothyroxine; D- -Tocopherol; D-ALPHA-tocopherol;
- English name: L-thyroxine
- English alias: L-Thyroxine; thx; L-Tyrosine, O- (4-hydroxy-3,5-diiodophenyl) -3,5-diiodo-; 3,5,3 ', 5'-tetraiodothyronine; THYROXINE;
- CAS number: 51-48-9
- Molecular formula: C 15 H 11 I 4 NO 4
- Molecular weight: 776.87000
- Exact mass: 776.68700
- PSA: 92.78000
- LogP: 5.25760
Physiochemical properties of levothyroxine
- Appearance and properties: beige powder
- Density: 2.635g / cm 3
- Melting point: 235 ° C
- Boiling point: 576.3ºC at 760mmHg
- Flash point: 302.3ºC
- Refractive index: 1.795
- Water solubility: insoluble
- Stability: Stable under normal temperatures and pressures.
- Storage conditions: 2-8ºC [1]
Levothyroxine related drug label information
Levothyroxine Basic Information
- [Alias] levothyroxine, levothyroxine, euthyroxine, levothyroxine sodium
- [Indications] Mainly used to prevent myxedema, cretinism and other hypothyroidism (such as obesity with low basal metabolic rate and habitual abortion, etc.), sometimes also used for acne, acral arterial spasm (Raynaud Disease) and constipation. Because this product can inhibit the release of pituitary thyroid stimulating hormone, it can be used to treat thyroid cancer, and it has a certain effect on breast cancer and ovarian cancer.
- [Dosage and usage] Myxedema: 0.1 to 0.2 mg each time, 3 times a day. Patients with coma were given a daily intravenous injection of 0.3 to 0.5 mg, and then changed to oral administration after waking. Obesity: Take 1-2mg orally 3 times a day. Children with congenital hypothyroidism, 0 to 6 months 25 to 50 g (8 to 10 g / kg); 6 to 12 months 50 to 70 g (6 to 8 g / kg); 1 to 5 years of age 75 to 100 g (5 to 5 6 g / kg); 150 to 200 g (2 to 3 g / kg) above 12 years old.
- [Precautions] Overdose can cause toxic reactions, such as palpitations, sweating, agitation, tremor, weight loss, elevated body temperature, central excitement and insomnia, and severe cases can cause vomiting, diarrhea, fever, tachycardia and irregularities, angina pectoris, muscles Vibrations and even cramps, heart failure, etc. Once it occurs, the drug should be discontinued for 1 week, and then start with a small dose. Diabetes, coronary heart disease patients are contraindicated.
- [Specifications] Tablet: 50g, 0.1mg; injection (sodium salt): 1mg / 10ml.
Levothyroxine pharmacological effects
- When the thyroid function is normal, T4 in blood T1 / 2 is about 6 to 7 days, when hypothyroidism is 9 to 10 days, and when hyperthyroidism is about 3 to 4 days, thyroxine is deiodinated in the surrounding tissue to form T3 and anti- T3, part of thyroxine is metabolized in the liver, and metabolites are excreted by bile. Thyroid hormones include thyroxine (T4) and triiodothyronine (T3). The adult thyroid gland secretes about T480 100g and T35 8g daily. [2]
Levothyroxine kinetics
- Target cell
- After free T3 and T4 enter the target cells, T4 is converted to T3, which has a 20-fold higher affinity with its receptor than T4. Therefore, T3 is the main active thyroid hormone, and T4 is regarded as a prohormone. Thyroid hormone has a wide range of effects on the body, has the role of promoting catabolism (thermogenesis) and anabolic metabolism, has an important impact on normal metabolism and growth and development of the human body, and is very important for the development of the central nervous system of infants and young children.
- The basic role of thyroid hormone is to induce the synthesis of new proteins, including special enzyme systems, to regulate the three major substances of protein, carbohydrates and fats, as well as the metabolism of water, salt and vitamins. Because thyroid hormone induces the synthesis of Na + -K + pump in the cell membrane and enhances its vitality, energy metabolism is enhanced.
- Thyroid hormone (mainly T3) binds to specific receptors in the nucleus. The latter undergoes a configuration change to form a dimer. The activated receptor combines with specific sequences on the DNA and thyroid hormone response elements to regulate genes. Transcription and expression (target genes of thyroid hormones) promote the synthesis of new proteins (mainly enzymes).
Levothyroxine indication
- thyroid
- Adjuvant drugs for antithyroid therapy to prevent the onset of hypothyroidism and further thyroid enlargement; Prevent the occurrence of thyroid cancer in patients with neck radiotherapy; Prevent goiter caused by certain drugs such as lithium, salicylic acid and sulfa drugs Effect; inhibitor of thyroid function test. This use is limited to T3.
Levothyroxine dosage
Levothyroxine orally
- Blood vessel
Levothyroxine injection
- Intravenous injection is suitable for patients with myxedema and coma. The first dose should be larger, 200 400g, and then 50 100g daily until the patient is awake and switched to oral administration. (1) The medication should be highly individualized, correctly grasp the dosage, and take the medicine daily on time. Those with hypothyroidism should generally be replaced for life. During treatment, they should be based on symptoms, signs and related laboratory tests (including T3, T4 or FT3, FT4, As a result, the dose was adjusted to maintain the FT3 or FT4 and the dose of the hypersensitivity TSH in the normal range as the optimal dose. (2) Avoid combination with other drugs, as it may interfere with the action of thyroid hormones.
Levothyroxine dose
- heart
Taking levothyroxine
- Patients with hypothyroidism with cardiovascular disease should pay attention to the occurrence of myocardial ischemia or arrhythmia. Thyroid hormones do not easily pass through the placenta, so patients with hypothyroidism do not need to stop medication during pregnancy. Trace amounts of thyroid hormones can be excreted from milk. T4 is used to treat low thyroid function. Due to its long half-life, the highest effect can be achieved 1 to 2 weeks after oral administration. The effect can be sustained for 1 to 3 weeks after stopping the drug. It only needs to be taken once a day. Because of its irregular absorption, it is best Taken on an empty stomach.
Levothyroxine adverse reactions
- Levothyroxine (Figure 2)
- Adverse reactions are similar to hyperthyroidism, such as increased appetite, nervousness, various types of tachycardia, arrhythmia, and increased basal metabolism. Allergic reactions caused by pure thyroid preparations were first reported in 1986. Patients with hypothyroidism developed fever, abnormal liver function, and increased eosinophils, and symptoms generally disappeared after drug withdrawal. For young people with hypothyroidism, T4 may cause short-term pseudoencephalopathy. If T4 is continuously used, even if there is no local neurological defect, headache and bilateral optic nerve papillary edema will appear.
- Acute thyroid poisoning may lead to the outbreak of clinical thyroid syndrome and death, but under normal circumstances, overdose will only cause temporary symptoms of hyperthyroidism. Dangerous conditions have been reported due to pharmacists mistakenly taking grams of T4 as a milligram dose to patients. T4, especially T3, is very dangerous to the heart if administered intravenously. Therefore, intravenous administration should be considered only in patients with life-threatening myxoid edema and with good cardiac monitoring. The use of dopamine drugs is more dangerous and should be used with caution.
Levothyroxine contraindications
Levothyroxine in elderly patients
- Adrenal gland
- The following situations should be used with caution:
- Cardiovascular diseases, including patients with angina pectoris, arteriosclerosis, coronary heart disease, hypertension, myocardial infarction, etc .;
- Patients with long course and severe thyroid hypothyroidism or myxedema should use caution when using this class of drugs, start with small doses, and then slowly increase until the physiological replacement dose;
- Patients with anterior pituitary hypofunction or adrenal insufficiency should use corticosteroids first, and then use this medicine after adrenal cortex function returns to normal.
Levothyroxine special patients
- For patients with heart disease and long-term hypothyroidism, the use of thyroid hormone replacement therapy is more dangerous, and adrenal insufficiency is often associated with hypothyroidism. If thyroid hormone replacement therapy precedes corticosteroid treatment, there may be Dyson's crisis, for patients with goiter, the secretion of thyroxine has always remained within the normal range. Due to the accumulation of endogenous thyroxine, a relatively small amount of exogenous hormones can cause excessive thyroid hormone and cause hyperthyroidism.
Levothyroxine drug interactions
- globulin
- (2) When thyroid hormone is used in combination with anticoagulants such as dicoumarin, the latter's anticoagulant effect is enhanced, which may cause bleeding; the dose of anticoagulant should be adjusted according to the prothrombin time.
- (3) When this class of drugs is combined with tricyclic antidepressants, the effects and toxic and side effects of both drugs are enhanced, and attention should be paid to adjusting the dose.
- (4) Those taking estrogen or contraceptives, due to an increase in the level of thyroxine-binding globulin in the blood, the dose of thyroid hormone is appropriately increased when combined.
- (5) Cholestyramine or cholestipol can reduce the effect of thyroid hormones. When two types of drugs are used, they should be taken at intervals of 4 to 5 hours, and the thyroid function should be measured regularly. (6) b Adrenergic blockers can reduce the conversion of T4 to T3 in peripheral tissues, and care should be taken when combined. T4 can increase the toxicity of cardiac glycosides and increase the effects of coumarins, anticoagulants and oral hypoglycemic agents. Clofibrate can increase the effect of T4.
Levothyroxine Specific Variety Information: Levothyroxine Sodium
About Levothyroxine
- Levothyroxine sodium: Pharmacodynamics Thyroid hormone is a derivative of iodinated tyrosine, including thyroxine and triiodothyronine. Normal people release 75 and 25 ug of T4 and T3, respectively. Thyroid hormone is necessary for the normal growth and development of the human body, and its insufficient or excessive secretion can cause disease. When the thyroid function is insufficient, both physical and mental development are affected, which can cause a small disease (cretinism), and when adult thyroid insufficiency, it can cause myxedema. Thyroid hormone can also promote material oxidation, increase oxygen consumption, increase basal metabolic rate, and increase heat production. Nervousness, irritability, tremor, increased heart rate, increased cardiac output, etc., occur during hyperfunction, because thyroid hormones can enhance the heart's sensitivity to catecholamines. [3]
Levothyroxine kinetics
- It is easily absorbed orally, and the plasma protein binding rate is over 99%. However, the affinity of T3 and protein is lower than T4, and its free amount can be 10 times that of T4. T3 has a fast and strong action and a short maintenance time, while T4 has a slow and weak action and a long maintenance time. The half-life is longer, T4 is 8 days, and T3 is 1 day. It is mainly deiodinated in the liver and kidney mitochondria, and is combined with glucaldehyde and sulfuric acid to excrete through the kidneys.
Levothyroxine indication
- Simple goiter (normal thyroid function); taken after goiter resection to prevent recurrence of goiter; can be used as a supplementary treatment for hypothyroidism caused by various reasons; adjuvant treatment of antithyroidism after thyroid function returns to normal ; Control and supplementary treatment of thyroid cancer, especially after thyroidectomy, can also be used for thyroid suppression experiments.
Levothyroxine dosage
- glucose
Levothyroxine considerations
- Urticaria
- Contraindications: Hyperthyroidism due to various reasons.
Levothyroxine Specific Variety Information: Levothyroxine Sodium Tablets
About Levothyroxine
- Amino acid
Levothyroxine kinetics
- Mitochondria
Levothyroxine considerations
- Elderly patients and patients with severe or long-term hypothyroidism should start with a small dose, increase the dose slowly, and frequently monitor the status of thyroid hormones. Especially for patients with coronary heart disease, heart failure or rapid arrhythmia, active measures must be taken to avoid mild hyperthyroidism caused by this drug. Hypothyroidism secondary to pituitary disease must determine whether there is adrenal insufficiency and, if present, must be treated with glucocorticoids. Effects on pregnancy and lactation During pregnancy and lactation, special treatment with thyroid hormones should be adhered to. It is contraindicated that levothyroxine and antithyroxine are used to treat hyperthyroidism during pregnancy because antithyroid hormones can cross the placenta. , And can cause fetal hypothyroidism.
Levothyroxine dosage
- Adults with simple goiter are 75-200ug / times / day, half an hour before breakfast, served with water, adolescents 50-150ug / times / day. Prevent goiter recurrence after goiter resection of 75-200ug / times / day. The initial dose of hypothyroidism in adults is 25-50ug / times / day, which is increased by 25-50ug every 2-4 weeks. Maintenance dose: 125-250ug / time / day. The initial dose for children is 25-50ug / times / day. The maintenance dose is 100-150ug / time / day. Adjuvant treatment of antihyperthyroidism 50-100ug / times / day. Thyroid suppression test 200ug / times / day. In children, if the heart function is normal, the full dose should be used at the beginning of treatment, but it should be started in small doses in adults and gradually increased to the optimal dose. [4]