Propylthiouracil

Propylthiouracil (PTU)

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Propylthiouracil (PTU)

Propylthiouracil is used to treat hyperthyroidism (overactive thyroid), Graves’ disease, or toxic goiter (enlarged thyroid). This medicine is sometimes given to control symptoms just before you undergo thyroid surgery or treatment with radioactive iodine.

Propylthiouracil is for use only if your condition cannot be treated with another thyroid medication, or when surgery or radioactive iodine are not good treatment options.

Propylthiouracil may also be used for purposes not listed in this medication guide.

Propylthiouracil

Why is this medication prescribed?

Propylthiouracil is used to treat hyperthyroidism (a condition that occurs when the thyroid gland produces too much thyroid hormone, speeding the body’s metabolism, and causing certain symptoms) in adults and children 6 years of age or older. Propylthiouracil is in a class of medications called antithyroid agents. It works by stopping the thyroid gland from making thyroid hormone.

How should this medicine be used?

Propylthiouracil comes as a tablet to take by mouth. It is usually taken three times a day, once every 8 hours. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take propylthiouracil exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor may decrease your dose of propylthiouracil once your condition is controlled.

Continue to take propylthiouracil even if you feel well. Do not stop taking propylthiouracil without talking to your doctor.

Contraindications

Previous severe hypersensitivity reaction e.g. agranulocytosis, hepatitis, vasculitis, nephritis.

Owing to the presence of Lactose, patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

Special warnings and precautions for use

Because of the risk of agranulocytosis it is advised that patients should be warned to report to their doctor in the event of a sore throat, fever, mouth ulcers, bruising, malaise, non-specific illness or other symptoms of infection immediately. A full blood count should be performed and treatment should be discontinued immediately if there is clinical or laboratory evidence of neutropenia.

Propylthiouracil may cause hypothrombinaemia and bleeding so prothrombin time should be monitored during therapy, especially prior to surgery.

Some cases of severe hepatic reactions, both in adults and children, including fatal cases and cases requiring a liver transplant have been reported with propylthiouracil. Time to onset has varied but in a majority of cases the liver reaction occurred within 6 months. If significant hepatic enzyme abnormalities develop during treatment with propylthiouracil the drug should be discontinued immediately.

Propylthiouracil should be used with caution in patients with renal impairment or hepatic disease. Patients should be advised of the symptoms of hepatic dysfunction (anorexia, pruritus, right upper quadrant pain, etc) and told to report them immediately. The occurrence of hepatic necrosis may have fatal consequences.

Interaction with other medicinal products and other forms of interaction

Drug induced changes in thyroid status may affect the dosage requirements for theophylline, digoxin or beta-blockers. The doses of theophylline, digoxin or beta-blockers may need to be reduced as thyroid function returns to normal.

Pre-treatment with propylthiouracil may reduce the effectiveness of radio-iodine (131I) therapy for hyperthyroidism. This is supported by four studies one of which, a randomised study in 80 patients, showed an approximate halving of cure rate one year after 131I therapy in patients pre-treated with propylthiouracil.

Side effects

The most common side effects are related to the skin and include rash, itching, hives, abnormal hair loss, and skin pigmentation. Other common side effects are swelling, nausea, vomiting, heartburn, loss of taste, joint or muscle aches, numbness and headache, allergic reactions, and hair whitening.

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Its notable side effects include a risk of agranulocytosis and aplastic anemia. On 3 June 2009, the FDA published an alert “notifying healthcare professionals of the risk of serious liver injury, including liver failure and death, with the use of propylthiouracil.” As a result, propylthiouracil is no longer recommended in non-pregnant adults and in children as the front line antithyroid medication

One possible side effect is agranulocytosis, a decrease of white blood cells in the blood. Symptoms and signs of agranulocytosis include infectious lesions of the throat, the gastrointestinal tract, and skin with an overall feeling of illness and fever. A decrease in blood platelets (thrombocytopenia) also may occur. Since platelets are important for the clotting of blood, thrombocytopenia may lead to problems with excessive bleeding. Side effects are suspected and the drug is sometimes discontinued if the patient complains of recurrent episodes of sore throat.

Another life-threatening side effect is sudden, severe, fulminant liver failure resulting in death or the need for a liver transplantation, which occurs in up to 1 in 10,000 people taking propylthiouracil. Unlike agranulocytosis which most commonly occurs in the first three months of therapy, this side effect may occur at any time during treatment.

Pregnancy

Propylthiouracil is classified as Drug Class D in pregnancy. Class D signifies there is positive evidence of human fetal risk. The maternal benefit may outweigh fetal risk in life-threatening situations. PTU is preferred over methimazole (which is also a class D) only in the first trimester of pregnancy and in women who may become pregnant because of the increased risk of teratogenicity of methimazole during critical organogenesis. In the second and third trimester, this risk is diminished and methimazole is preferred to avoid the risk of liver complications from PTU in the mother.

Lactation

Propylthiouracil also transfers to breast milk but this does not preclude breast-feeding. Neonatal development and infant thyroid function should be closely monitored. The lowest effective dose should be used.

Warnings

Propylthiouracil may cause severe liver damage in adults and children. Some people who took propylthiouracil needed liver transplants and some people died because of the liver damage. Because of this risk, propylthiouracil should only be given to people who cannot receive other treatments such as surgery, radioactive iodine, or a different medication called methimazole (Tapazole). Propylthiouracil may also be given to women during the first months (about 12 weeks) of pregnancy because methimazole may cause birth defects if it is used during this part of a pregnancy.

If you are taking propylthiouracil, call your doctor immediately if you develop any of the following symptoms: fever, loss of appetite, nausea, vomiting, tiredness, itching, dark urine, pale or light colored stools, yellowing of the skin or eyes, or pain in the upper right part of the stomach.

Your doctor or pharmacist will give you the manufacturer’s patient information sheet (Medication Guide) when you begin treatment with propylthiouracil and each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions. You can also visit the Food and Drug Administration (FDA) website (http://www.fda.gov/Drugs/DrugSafety/ucm085729.htm).

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