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propylthiouracil

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GENERIC NAME: propylthiouracil

BRAND NAME: None available

DRUG CLASS AND MECHANISM: Propylthiouracil (PTU) is used to manage hyperthyroidism which is due to an overactive thyroid gland. It is considered an anti-thyroid agent, like methimazole (Tapazole).

Grave's disease is the most common cause of hyperthyroidism. It is an autoimmune disease where an individual's own antibodies attach to thyroid stimulating hormone receptors within cells of the thyroid gland and then trigger overproduction of thyroid hormone. The two thyroid hormones manufactured by the thyroid gland, thyroxine (T4 ) and triiodothyronine (T3), are formed by combining iodine and a protein called thyroglobulin with the assistance of an enzyme called peroxidase. PTU inhibits iodine and peroxidase from their normal interactions with thyroglobulin to form T4 and T3. This action decreases thyroid hormone production. (PTU also interferes with the conversion of T4 to T3, and, since T3 is more potent than T4, this also reduces the activity of thyroid hormones.)

GENERIC AVAILABLE: yes

PRESCRIPTION: yes

PREPARATIONS: Tablet: 50mg.

STORAGE: PTU should be stored at room temperature, 15-30°C (59-86°F).

PRESCRIBED FOR: PTU is used to manage hyperthyroidism associated with Grave's disease. It is also used to decrease symptoms of hyperthyroidism in preparation for surgically removing the thyroid gland or before inactivating the thyroid gland with radioactive iodine therapy. PTU may also be used when it is not advisable to remove the thyroid gland.

DOSING: The initial adult dose of PTU is 300 mg/day. The drug should be taken every eight hours. Occasionally adult doses may exceed 300 mg/day if moderate or severe hyperthyroidism is present. A common, long-term adult dose after initial treatment is 100-150 mg/day. Children's initial and continuing doses vary.

DRUG INTERACTIONS: PTU may increase the effect of oral blood thinners, for example warfarin (Coumadin). Therefore, warfarin dose changes and monitoring for the effects of warfarin on blood clotting are necessary.

PREGNANCY: There is evidence that PTU may cause harm to the fetus during pregnancy. If hyperthyroidism becomes more severe during pregnancy, however, PTU may be considered useful under physician supervision.

NURSING MOTHERS: There is evidence that PTU may cause harm to the fetus during nursing. Use of PTU while nursing should be done under careful physician supervision.

SIDE EFFECTS: PTU is generally well-tolerated with side effects occurring in 1 of every 100 patients. 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.

Less common but serious side effects have occurred with PTU therapy. A decrease of white blood cells in the blood (agranulocytosis) may occur. 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.

There also have been rare occurrences with PTU of hepatitis and death of liver cells (hepatic necrosis). Failure of the liver due to hepatic necrosis may lead to severe brain swelling, gastrointestinal bleeding, and death.

Reference: FDA Prescribing Information

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