Some learning points about levothyroxine.📝📝📝

The manual for levothyroxine.

Indications:

1. Treatment of non-toxic goiter with normal thyroid function.
2. After goiter resection, prevent the recurrence of goiter.
3. Adjuvant treatment of hyperthyroidism with antithyroid drugs.
4. Suppressive treatment after thyroid cancer surgery.
5. Alternative treatment of hypothyroidism caused by various reasons.
6. Thyroid suppression test (used in diagnosis and treatment of diseases).

In addition, levothyroxine is not used for weight loss. It is because inappropriate long-term use of levothyroxine can cause various complications of hyperthyroidism and even life-threatening.

Some moderate to severe obesity patients may have subclinical hypothyroidism. Thyroid stimulating hormone is compensatory elevated, but thyroid hormone levels are normal. Consider taking a small dose of levothyroxine sodium tablets (such as 25ug/day) within a certain period of time. It can reduce the level of thyroid-stimulating hormone and increase the basal metabolic rate, which may help weight loss, but also should pay attention to adverse reactions and strengthen thyroid function.

Medicine interactions:

For drugs that affect the absorption of levothyroxine, you can increase the interval or increase the dose:

1. Cholesterol-lowering drugs: such as cholestyramine and colestipol.
2. Drugs containing aluminum, iron and calcium. Such as gastric mucosal protective agent (sucralfate), antacids (aluminum hydroxide, ferrous sulfate, calcium carbonate tablets).
3. Acid inhibitors and stomach drugs: H2 receptor blockers and proton pump inhibitors (such as ranitidine, omeprazole).
4. Anti-epileptic drugs: such as phenobarbital, phenytoin sodium, carbamazepine.
5. Anti-tuberculosis drugs: such as rifampicin.

Drugs affected by levothyroxine:

1. Anti-diabetic drugs: Levothyroxine can reduce the effect of hypoglycemic. Therefore, patients with diabetes should increase blood glucose monitoring and adjust the dosage in time.
2. Anticoagulant: Levothyroxine can enhance the anticoagulant effect of coumarin derivatives (such as warfarin). Patients should pay attention to adjusting the dosage to prevent the risk of bleeding.

Others:

Propylthiouracil, amiodarone, iodine-containing contrast agents and β-sympathomimetic drugs, glucocorticoids, estrogen, sertraline, etc. can reduce the efficacy of the drug. Salicylate, dicoumarin, high-dose furosemide (250mg), oxytocin, phenytoin, etc. can increase the efficacy of the drug. Need to adjust the dose of levothyroxine sodium tablets as appropriate.

Foods:

Animal offal, spinach, cherries, grapes, peaches, grapefruit, soybeans, high-fiber foods, coffee, milk, yogurt, soy milk, etc.

Medication time:

Since food can affect the absorption of levothyroxine sodium tablets, it is recommended to take the dose with water every morning on an empty stomach. It can be taken immediately after getting up in the morning, but do not eat breakfast within half an hour.

If the dose of the drug is large, it is still not necessary to take it in divided doses. Try not to take the medicine before going to bed, otherwise it may increase the excitability of the body and affect the quality of sleep.

Dosage:

The blood level of thyroid stimulating hormone is a reliable basis for determining the dosage of treatment. If the child has no obvious contraindications, the full dose should be used at the beginning of treatment or the optimal dose can be reached quickly in a short period of time. However, adults should start with a small dose and gradually increase to the optimal dose every 2 to 4 weeks. Elderly patients should increase the dose more slowly.

1. Goiter (normal thyroid function): 75-200ug/day for adults, 50-150ug/day for teenagers.
2. Prevention of goiter recurrence after thyroidectomy: 75-200ug/day for adults.
3. Hypothyroidism in adults: initial dose 25-50ug/day, increase 25-50ug every 2-4 weeks, maintenance dose 125-250ug/day.
4. Hypothyroidism in children: the initial dose is 12.5-50ug/day/m² body surface area, and the maintenance dose is 100-150ug/day/m² body surface area.
5. Adjuvant treatment of anti-hyperthyroidism: 50-100ug/day. After total thyroidectomy: 150-300ug/day.
6. Thyroid suppression test: 200ug/day.

Monitor:

At the beginning of treatment and every time the dosage is adjusted, thyroid function needs to be measured every 4 to 6 weeks. Adjust the dose according to the inspection results. After the treatment reaches the standard, check again every 6 to 12 months. If the treatment is not up to standard, you should carefully look for the reasons, such as clinical compliance and medication time.

Adverse reactions:

Levothyroxine is generally well tolerated. Patients who increase the dose too quickly in the early stage of treatment or overdose may have symptoms of hyperthyroidism, such as palpitations, tremor, sweating, skin flushing, diarrhea, weight loss, menstrual disorders, insomnia and irritability.

When the patient has any adverse reactions, appropriate treatment should be given. If necessary, reduce the dose or discontinue the drug until the adverse reaction disappears and then start the treatment from a small dose.

Long-term use of levothyroxine can accelerate the bone transformation process. Elderly and postmenopausal patients with osteoporosis should pay attention to calcium and vitamin D supplementation. They should monitor the bone density regularly.

Missed medication:

The half-life of levothyroxine is 7 days and its effect is slow and lasting. The effect is significant and stable after taking the medicine one month. 

In the early treatment of hypothyroidism, if there is a missed dose, it may be considered supplementing the dose on the same day or doubling the dose the next day. If the thyroid function is relatively stable after taking the medicine regularly for a long time, it may be considered that there is no need to take supplements, and it can be maintained at the current dose.

Patients after thyroid cancer surgery should ensure that they do not miss a dose as much as possible. If a missed dose is taken, it should be refilled in time to ensure that the dose is sufficient for at least the entire week.

Special population:

At the recommended dose, levothyroxine is not teratogenic to the fetus, nor will it interfere with fetal thyroid function. Therefore, women during pregnancy and lactation cannot stop levothyroxine treatment. The dose may need to increase during pregnancy. Hypothyroidism caused by drug withdrawal has a great impact on maternal and fetal development. Levothyroxine cannot be used as an adjuvant treatment for hyperthyroidism during pregnancy, as this will increase the dose of antithyroid drugs and increase the risk of suppressing fetal thyroid function.

Patients with coronary heart disease, elderly, severe or long-term hypothyroidism must be very cautious about the dose of levothyroxine. It must be started with a small dose, the interval between dose increases should be lengthened, and the monitoring of thyroid function should be strengthened.

Patients with after thyroid cancer surgery take levothyroxine on the one hand to supplement thyroid hormones to prevent hypothyroidism, and on the other to inhibit thyroid stimulating hormone to prevent cancer recurrence.

Contraindications:

1. Allergy.
2. Untreated adrenal insufficiency, pituitary insufficiency, hyperthyroidism, coronary heart disease, angina pectoris, arteriosclerosis and high blood pressure.
3. Acute myocardial infarction, acute myocarditis.