Drug Groups

approved

Description

A thiourea antithyroid agent. Propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to tri-iodothyronine. It is used in the treatment of hyperthyroidism. (From Martindale, The Extra Pharmacopeoia, 30th ed, p534)

Indication

Used to manage hyperthyroidism which is due to an overactive thyroid gland (Grave's disease).

Pharmacology

Propylthiouracil is a thiourea antithyroid agent. 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. The actions and use of propylthiouracil are similar to those of methimazole.

Toxicity

Oral, rat: LD₅₀ = 1250 mg/kg.

Affected Organisms

Absorption

Well absorbed following oral administration.

Half Life

2 hours

Protein Binding

82%

Elimination

Propylthiouracil is readily absorbed and is extensively metabolized. Approximately 35% of the drug is excreted in the urine, in intact and conjugated forms, within 24 hours.

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