Indications
Propylthiouracil is used to treat an overactive thyroid gland (hyperthyroidism), including Graves’ disease. It is also used to control thyroid levels before thyroid surgery or radioactive iodine treatment, and it is often the preferred choice in the first three months of pregnancy and in thyroid storm (a severe, sudden worsening of hyperthyroidism).
How It Works
The thyroid gland uses iodine to make thyroid hormones. Propylthiouracil blocks the enzyme that builds these hormones, so less hormone is made. It also reduces the conversion of the stored hormone T4 into the more active T3 in the body, which helps symptoms such as a fast heartbeat, tremor and weight loss settle down over a few weeks.
Dosage and Administration
The dose is set by your doctor according to your thyroid blood tests and is usually higher at the start and then reduced to a lower maintenance dose. Take it exactly as prescribed, usually in divided doses spread through the day, with or without food. Do not stop suddenly unless your doctor tells you to. Regular blood tests are needed to check thyroid levels, liver function and blood counts.
Interactions
- Blood thinners such as Warfarin: the effect may change, so clotting tests may need checking.
- Medicines for heart rate such as beta blockers and Digoxin: doses may need adjusting as thyroid levels return to normal.
- Theophylline: blood levels may change as thyroid function changes.
- Other medicines that can affect the liver or lower white blood cells.
Tell your doctor about all medicines, herbal products and supplements you take.
Contraindications
Do not take Propylthiouracil if you are allergic to it, have had serious liver damage or a severe blood disorder (such as agranulocytosis) from it before, or have severe existing liver disease.
Side Effects
Common side effects include rash, itching, nausea, stomach upset, joint pain, headache and changes in taste. Less common but serious effects include liver injury, a sharp fall in white blood cells (agranulocytosis), which lowers your ability to fight infection, and inflammation of blood vessels (vasculitis).
Get urgent medical help if you develop a sore throat, fever, mouth ulcers or any sign of infection, yellowing of the skin or eyes, dark urine, pale stools, severe tiredness, loss of appetite, pain in the upper right side of the abdomen, unusual bleeding or bruising, or a severe rash. Stop taking the tablets and contact your doctor straight away.
Pregnancy and Lactation
Untreated hyperthyroidism is risky in pregnancy. Propylthiouracil is often preferred in the first trimester, after which doctors may switch to another medicine because of the liver risk. Small amounts pass into breast milk and it is generally considered acceptable while breastfeeding at the lowest effective dose, with the baby’s thyroid checked if needed. Always follow your doctor’s advice.
Precautions and Warnings
Propylthiouracil can cause severe liver damage, so report any liver symptoms at once. Your doctor will check your blood counts and liver tests. Too high a dose can make the thyroid underactive, causing tiredness, weight gain and feeling cold. Tell your doctor before any surgery. Use extra care in the elderly and in people with existing liver problems.
Overdose
An overdose may cause nausea, vomiting, stomach pain, headache, fever and joint pain, and over time can lead to an underactive thyroid or bone marrow problems. Seek medical help straight away and take the medicine pack with you.
Therapeutic Class
Antithyroid medicine (thioamide).
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.