Letrox – composition, action, dosage, side effects, duration of treatment

Proven content

Letrox is a prescription medicine that is a synthetic thyroid hormone. It is used in people who struggle with diseases of the thyroid gland. It is available in several variants – depending on the dose of the active substance.

Letrox — what kind of drug is it?

Letrox is a drug that contains the thyroid hormone levothyroxine as an active ingredient. This substance works in the same way as a naturally produced hormone. Letrox is used to replace the deficiency of the thyroid hormone and / or to relieve the problems with the functioning of the thyroid gland. Letrox is recommended for use in the case of:

1. supplementing the deficiency of thyroid hormones in hypothyroidism,
2. preventing the return of goiter (thyroid enlargement) after surgery in patients with normal thyroid function,
3. treatment of benign goiter in patients with normal thyroid function,
4. as an aid in the treatment of hyperthyroidism in combination with thyreostatic drugs (drugs that suppress the activity of the thyroid gland) after normal thyroid function is achieved,
5. treatment of malignant neoplasms of the thyroid gland, especially after surgery to remove the thyroid gland, in order to inhibit tumor growth and replenish the deficiency of thyroid hormones,
6. a thyroid function test (thyroid suppression test).

Letrox is available in the following forms:

1. Letrox 50,
2. Letrox 75,
3. Letrox 100,
4. Letrox 125,
5. Letrox 150.

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Letrox – composition and mechanism of action

Each Letrox tablet contains:

1. calcium hydrogen phosphate dihydrate,
2. microcrystalline cellulose,
3. sodium carboxymethyl starch (type A),
4. right-handed,
5. long chain glycerides.

In addition, depending on the type of drug Letrox, the content of the active substance is as follows:

1. Letrox 50 micrograms contains 53,2 – 56,8 micrograms of levothyroxine sodium (Levothyroxinum natricum) x H2O (equivalent to 50 µg of levothyroxine sodium),
2. Letrox 75 micrograms contains 79,8 – 85,2 micrograms of levothyroxine sodium (Levothyroxinum natricum) x H2O (equivalent to 75 µg of levothyroxine sodium),
3. Letrox 100 contains 106,4 – 113,6 micrograms of levothyroxine sodium (Levothyroxinum natricum) x H2O (equivalent to 100 µg of levothyroxine sodium),
4. Letrox 125 micrograms contains 133-142 micrograms of levothyroxine sodium (Levothyroxinum natricum) x H2O (equivalent to 125 µg of levothyroxine sodium),
5. Letrox 150 contains 159,6 – 170,4 micrograms of levothyroxine sodium (Levothyroxinum natricum) x H2O (corresponding to 150 µg of levothyroxine sodium).

Synthetic levothyroxine, which is an active ingredient Letrox works in the same way as a naturally occurring hormone mainly produced by the thyroid gland. The body is unable to distinguish between endogenous and exogenous levothyroxine.

Letrox should be taken on an empty stomach. After oral administration in the fasted state, 80% of levothyroxine is absorbed mainly in the upper part of the small intestine, depending on the form of the drug. This absorption is significantly limited when the product is administered with a meal.

Peak serum levels are reached approximately 2 to 3 hours after administration. Upon initiation of oral therapy, the therapeutic effect develops within 3 to 5 days. The half-life of levothyroxine is approximately 7 days. In hyperthyroidism it is shorter (3-4 days) and in hypothyroidism it is longer (about 9-10 days).

See: What tests should be performed on a sick thyroid?

Letrox – dosage

Letrox should be taken in the morning on an empty stomach, at least half an hour before breakfast, with a sufficient amount of water. Children should receive the total daily dose at least half an hour before the first meal. The tablets can also be administered as a suspension. The tablets should be dissolved in the appropriate amount of water (10-15 ml), and the resulting suspension, which should be prepared fresh each time, should be administered with an additional amount of liquid (5-10 ml).

The individual daily dose should be established on the basis of a medical examination and the results of laboratory tests. In case of persistent residual thyroid function, lower doses may be appropriate.

Treatment with thyroid hormones should be carried out with particular caution in the elderly, people with coronary heart disease and people with severe or prolonged hypothyroidism. In these individuals, treatment should be started with a low initial dose and then increased slowly over long periods while monitoring the thyroid hormone levels.

Dosing of Letrox is as follows:

overactive thyroid gland:

1. initial dose – 25 to 50 micrograms of levothyroxine sodium / day,
2. maintenance dose – 100 to 200 micrograms of levothyroxine sodium / day.

The dose of Letrox should be increased by 25-50 µg at intervals of 2-4 weeks.

goiter relapse prevention:

1. 75 to 200 micrograms of levothyroxine sodium / day

Benign goiter in patients with euthyroidism:

1. 75 to 200 micrograms of levothyroxine sodium / day

therapy supporting the thyrostatic treatment of hyperthyroidism:

1. 50 to 100 micrograms of levothyroxine sodium / day

after surgery to remove the thyroid gland due to malignant neoplasms of the thyroid gland:

1. 150 to 300 micrograms of levothyroxine sodium / day

suppression test in the diagnosis of hyperthyroidism:

1. 200 micrograms (for 14 days until scintigraphy is performed).

In neonates and infants with congenital hypothyroidism, the recommended starting dose is 10 to 15 micrograms of levothyroxine sodium per kg of body weight per day for the first 3 months. Thereafter, the dose should be adjusted individually, based on the clinical picture, thyroid hormone levels and TSH values.

In children with acquired hypothyroidism, the recommended starting dose is 12,5 to 50 micrograms of levothyroxine sodium daily. The dose should be gradually increased every 2 to 4 weeks, depending on the clinical findings and thyroid hormone levels and TSH values, until the full replacement dose is achieved.

Letrox – length of treatment

In the case of hypothyroidism and after thyroid removal surgery for malignant thyroid neoplasm, treatment is usually life-long, and for benign goiter and relapse prevention, treatment lasts several months or years, or even for the rest of your life.

In the case of adjunctive therapy in the treatment of hyperthyroidism, the duration of treatment depends on the duration of thyrostatic therapy. Treatment of goiter in euthyroid patients should last from 6 months to 2 years. If treatment with Letrox does not produce the desired therapeutic effect within this time frame, alternative treatment options should be considered.

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Letrox – contraindications and precautions

In some cases, Letrox cannot be used. The main contraindications for the use of Letrox are:

1. hypersensitivity to the active substance or to any of the excipients of Letrox,
2. untreated hyperthyroidism
3. untreated adrenal insufficiency
4. Untreated pituitary insufficiency (in adrenal insufficiency requiring
5. treatment),
6. acute myocardial infarction,
7. acute myocarditis,
8. acute inflammation of the heart.

Before starting Letrox, a treatment with thyroid hormone, the following diseases or conditions should be ruled out or treated with appropriate therapy:

1. coronary artery disease,
2. angina,
3. hypertension,
4. hypopituitarism or adrenal cortex,
5. an autonomic nodule.

These conditions should also be ruled out or treated before performing a thyroid suppression test, with the exception of autonomic thyroid function, which may lead to a thyroid suppression test. Adrenal cortex disorders should be initiated prior to initiation of treatment with levothyroxine with appropriate replacement therapy to prevent acute adrenal insufficiency.

1. Thyroid doctor – endocrinologist or thyroidologist?

In people suffering from coronary artery disease, heart failure, arrhythmias with tachycardia, non-acute myocarditis, long-term hypothyroidism or in people with a history of myocardial infarction, even mild drug-induced hyperthyroidism should be strictly avoided. These people may need to monitor their thyroid hormone levels more frequently when treating with thyroid hormones.

When initiating treatment with levothyroxine (Letrox) in preterm infants with very low birth weight, haemodynamic parameters should be monitored as circulatory collapse due to immature adrenal function may occur.

Caution should be exercised when administering Letrox to people with epilepsy as these people have an increased risk of seizures. When using Letrox in postmenopausal women with an increased risk of osteoporosis, the lowest effective dose should be selected and thyroid function should be monitored more frequently to avoid higher than physiological levels of levothyroxine in the blood serum.

Thyroid hormones must not be used for weight loss. In people with normal thyroid function, the usual doses do not reduce body weight.

See: Thyroid ultrasound – how to interpret the results?

Letrox – interactions with other medications

Letrox, especially its active substance, levothyroxine sodium, may adversely affect the action of other medications taken. Be especially careful if you are taking the following medications:

antidiabetic drugs – levothyroxine may reduce the effect of anti-diabetic drugs that lower blood sugar levels,

coumarin derivatives – levothyroxine may potentiate the effects of coumarin derivatives by displacing them from their protein boundaries. In case of concomitant use of these drugs, the blood coagulation parameters should be regularly monitored and, if necessary, the dose of the anticoagulant should be adjusted accordingly (reduce the dose).

ion exchange resins – ion exchange resins such as cholestyramine, colestipol, calcium and sodium polystyrene sulfonic acid inhibit the absorption of levothyroxine by binding to thyroid hormones in the gastrointestinal tract and therefore should be administered 4 to 5 hours after taking Letrox.

bile acid sequestrants – colesevelam binds levothyroxine and thus reduces the absorption of levothyroxine from the gastrointestinal tract. No interaction was observed when levothyroxine was administered at least 4 hours prior to the intake of colesevelam. Therefore, Letrox should be given at least 4 hours before taking colesevelam.

aluminum-containing antacids, iron-containing drugs, calcium-containing drugs – the absorption of levothyroxine may be impaired in the case of simultaneous administration of aluminum-containing antacids (antacids, sucralfate), iron-containing drugs and calcium-containing drugs. Letrox should be administered at least 2 hours before their intake,

sevelamer and lanthanum carbonate – sevelamer and lanthanum carbonate may reduce the bioavailability of levothyroxine,

propylthiouracil, glucocorticoids and beta-blockers (especially propranolol) – these substances inhibit the conversion of T4 to the T3 form of the hormone and lead to a decrease in the concentration of the T3 fraction in the blood serum,

amiodarone and iodinated contrast agents – amiodarone and iodinated contrast media, due to their high iodine content, can cause both hypothyroidism and hyperthyroidism. Due to the risk of an autonomic nodule, the patient’s condition should be carefully monitored if its autonomy is suspected. Amiodarone inhibits the conversion of T4 to the T3 form of the hormone, which consequently reduces the concentration of the T3 fraction and increases the concentration of TSH in the blood serum. As a result of such effects of amiodarone on thyroid function, the dose of Letrox may need to be adjusted.

salicylany, dikumarol, furosemid, klofibrat – levothyroxine may be displaced from serum protein binding by salicylates (especially at doses higher than 2,0 g daily), dicoumarol, high doses of furosemide (250 mg), clofibrate and other drugs. This may lead to an initial transient increase in plasma levels of free thyroid hormones followed by a complete decline.

contraceptives containing estrogen, hormone replacement therapy drugs after the menopause – During the use of contraceptives containing oestrogens and during postmenopausal hormone replacement therapy, the need for levothyroxine may increase. Increased levothyroxine binding may occur, which may lead to diagnostic and therapeutic errors.

sertralina, chlorochina/ proguanil – these substances reduce the effectiveness of levothyroxine and increase serum TSH levels,

drugs with enzyme-inducing properties – barbiturates, rifampicin, carbamazepine, phenytoin and other drugs with hepatic enzyme-inducing properties may increase the hepatic clearance of levothyroxine and lead to decreased plasma concentrations,

soy products – soy products can reduce the intestinal absorption of levothyroxine. Increased serum TSH levels have been reported in children with congenital hypothyroidism on a soy-rich diet treated with levothyroxine. Extremely high doses of levothyroxine may be required to obtain the correct values ​​for T4 and TSH levels. Serum T4 and TSH levels should be closely monitored during and after a diet rich in soy products, and the levothyroxine dose may need to be adjusted in some cases.

Letrox – pregnancy and breastfeeding

If a woman is pregnant or breastfeeding, thinks she may be pregnant or is planning to have a baby, ask your doctor or pharmacist for advice before taking Letrox.

Treatment with thyroid hormones should be carried out continuously during pregnancy and lactation. The proper concentration of thyroid hormone is important to ensure optimal health for the mother and the fetus. Despite the extensive use of levothyroxine during pregnancy, its negative effects on the course of pregnancy or on the health of the fetus / newborn child remain unknown.

The amount of thyroid hormone excreted in human milk during lactation, even when treated with high doses of levothyroxine, does not constitute a dose sufficient to develop hyperthyroidism or inhibit TSH secretion in the infant. During pregnancy, the requirement for levothyroxine may increase due to circulating estrogens. Therefore, thyroid function should be monitored both during and after pregnancy, and the dose of levothyroxine adjusted if necessary.

Letrox – side effects

In isolated cases, if the recommended dose of Letrox is not tolerated or an overdose has occurred, especially if the dose is increased too quickly at the start of treatment, typical symptoms of an overactive thyroid gland may occur.

If these symptoms occur, reduce the daily dose of Letrox or interrupt it for several days. Treatment can be resumed with careful dosing when symptoms resolve.

The side effects of Letrox may include:

1. heart problems – palpitations, tachycardia, arrhythmias, angina,
2. disorders of the skin and subcutaneous tissue – angioedema, rash, urticaria, hyperhidrosis,
3. mental disorders – insomnia, nervousness, anxiety,
4. musculoskeletal and connective tissue disorders – muscle weakness, muscle spasms, osteoporosis with suppressive doses of levothyroxine, especially in postmenopausal women, mainly during long-term treatment,
5. vascular disorders – hot flushes, vascular collapse in premature babies with low birth weight,
6. reproductive system and breast disorders – menstrual disorders,
7. gastrointestinal disorders – diarrhea, vomiting,
8. nervous system disorders – headaches, brain tumor (especially in children), tremors.