Brands, Medical Use, Clinical Data
Drug Category
- Antithyroid Agents
- Antimetabolites
Dosage Forms
Brands / Synonyms
Procasil; Propacil; Propilthiouracil; Propycil; Propyl-Thiorist; Propyl-Thiorit; Propyl-Thyracil; Propylthiorit; Propylthiouracil; Propylthiouracil Ph Eur; Propythiouracil; Prothiucil; Prothiurone; Prothycil; Prothyran; Protiural; PTU; Thiuragyl; Thyreostat II
Indications
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.
Mechanism of Action
Propylthiouracil binds to thyroid peroxidase and thereby inhibits the conversion of iodide to iodine. Thyroid peroxidase normally converts iodide to iodine (via hydrogen peroxide as a cofactor) and also catalyzes the incorporation of the resulting iodide molecule onto both the 3 and/or 5 positions of the phenol rings of tyrosines found in thyroglobulin. Thyroglobulin is degraded to produce thyroxine (T4) and tri-iodothyronine (T3), which are the main hormones produced by the thyroid gland. Therefore propylthiouracil effectively inhibits the production of new thyroid hormones.
Absorption
Well absorbed following oral administration.
Toxicity
Oral, rat: LD50 = 1250 mg/kg.
Biotrnasformation / Drug Metabolism
Not Available
Contraindications
Contraindicated in patients with kidney failure or liver disease.
Drug Interactions
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.
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