What is it used for?

• Correcting very low thyroid hormone levels as a result of an underactive thyroid gland (hypothyroidism). This medicine is given when it is necessary to rapidly correct thyroid hormone levels.

How does it work?

• Liothyronine is one of the thyroid hormones produced by the thyroid gland.
• The thyroid gland produces and releases two hormones: liothyronine (T3) and thyroxine (T4). Thyroxine is converted to liothyronine in other areas of the body. Liothyronine is the more active hormone in the body. It is responsible for maintaining a normal rate of metabolism for the whole body.
• When the thyroid gland is unable to produce normal amounts of liothyronine and thyroxine, the blood levels of these thyroid hormones decrease (this is known as an underactive thyroid gland or hypothyroidism). Extremely low levels of thyroid hormones can result in a condition known as myxoedema. Myxoedema can involve many symptoms such as hair loss and blood disorders. In extreme cases this condition may result in psychosis or coma.
• Liothyronine is given when thyroid homrones fall very low and rapid replacement is needed. Liothyronine does not have to be converted from thyroxine and can therefore act quickly (within a few hours).
• Liothyronine is given to rapidly replace the liothyronine that would normally have been produced by the thyroid gland. It doesn't stimulate the thyroid gland to produce greater amounts of thyroid hormones; it simply acts to quickly return the blood levels of liothyronine to normal levels.

Liothyronine may be given as tablets or injection.

Warning!

• You will need to have regular blood tests to monitor your levels of thyroid hormones while taking this medicine. This will enable your doctor to prescribe you the correct dose to increase levels of your thyroid hormones into the normal range.
• Certain medicines can interfere with blood tests that you have to determine your thyroid hormone levels (thyroid function tests). It is important to inform your doctor of all the medicines you are taking prior to and at the time of blood tests.

Use with caution in

• Elderly people.
• Heart disease.
• Diabetes mellitus.
• Rare disease where there is a problem with the kidneys that causes large amounts of dilute urine to be produced (diabetes insipidus).
• People who have had an underactive thyroid gland for a long time.
• People whose adrenal glands are also underactive. In prolonged and severe hypothyroidism, the adrenal glands can become less active. When treatment with this medicine is started, the thyroid hormones and hence the body's metabolism increase faster than adrenal glands recover, and as a result the adrenal glands may not produce sufficient levels of natural steroid hormones.

Not to be used in

• Overactive thyroid gland (hyperthyroidism or thyrotoxicosis).
• This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

• Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
• Liothyronine can be taken during pregnancy as it does not cross the placenta in significant amounts. However, it is important that pregnant women have regular blood tests to monitor their levels of thyroid hormones during the pregnancy. Seek further medical advice from your doctor.
• Thyroid hormones pass into breast milk, but in amounts that are too small to affect the nursing baby, or to affect tests for neonatal hypothyroidism. It is safe for women taking this medicine to breastfeed their babies. Seek further medical advice from your doctor.

Side effects

Side effects caused by liothyronine usually only occur if your dose is too high. For this reason, you should tell your doctor if you get any of the following side effects.

• Chest pain (angina).
• Awareness of your heart beat (heart palpitations).
• Abnormal heart beats (arrhythmias).
• Faster than normal heart beat (tachycardia).
• Headache.
• Diarrhoea.
• Restlessness.
• Excitability.
• Muscle cramps.
• Sweating.
• Flushing.
• Muscle weakness.
• Weight loss.

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

Liothyronine may increase the anti-blood-clotting effect of anticoagulant medicines such as warfarin. This may increase the risk of bleeding. People taking liothyronine in combination with an anticoagulant such as warfarin should have their blood-clotting time (INR) regularly monitored, particularly after any changes in the dose of liothyronine. The dose of the anti-clotting medicine may need to be decreased.

The following medicines may increase the breakdown of liothyronine by the body. If you start or stop treatment with one of these medicines while you are taking liothyronine, your liothyronine dose may need to be adjusted:

• antiepileptic medicines such as phenytoin and carbamazepine
• barbiturates such as amobarbital.

Colestipol and colestyramine decrease the absorption of liothyronine from the gut and should not be taken within four to six hours of taking liothyronine.

People taking digoxin or theophylline may need a gradual increase in their digoxin or theophylline dose as this medicine returns thyroid function to normal. This is because the dose of these medicines that is needed can be affected by the level of thyroid hormones in the blood.

References:

https://www.drugs.com/international/thybon-20-henning.html

https://www.whatdotheyknow.com/request/forms_to_be_signed_by_gp_to_pres

https://www.medicines.org.uk/emc/product/5905/smpc#gref

https://www.ndrugs.com/?s=thybon%2020%20henning

https://www.sdrugs.com/?c=drug&s=thybon

https://www.bennewitz.com/scat/scatpharm?command=listitems&type=search&search=thybon+20&lang=en

https://www.netdoctor.co.uk/medicines/a7641/liothyronine/