Drug reference

Propylthiouracil

Antithyroid

CDSCO approvedSchedule H

EXCRETION

—

not curated

INTERACTIONS

7 major

SEVERE in our sources

PREGNANCY

Drug of choice during the first trimester; consider switching to carbimazole in the second trimester due to potential hepatotoxicity risk. Crosses the placenta and high doses may cause fetal goitre and hypothyroidism; use the lowest dose that will control the hyperthyroid state.

FDA category + note

Top interactionssee all 7 →

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Mechanism

Propylthiouracil is an antithyroid drug that primarily interferes with the synthesis of thyroid hormones. It achieves this by inhibiting the enzyme thyroid peroxidase, which is responsible for the iodination of tyrosine residues on thyroglobulin and the coupling of these iodotyrosines to form T4 and T3.

Indications

HyperthyroidismThyrotoxic crisissevere hyperthyroid states (thyroid storm)Graves diseaseThyrotoxicosis (Graves’ disease, toxic nodular goiter)Thyroid storm (preferred for inhibitory action on peripheral conversion of T4 to T3)

Dosing

Adult: ▶ BY MOUTH Antithyroid drugs in pregnancy Radioactive iodine therapy is contra-indicated during pregnancy. Propylthiouracil and carbimazole can be given but the blocking-replacement regimen is not suitable. Carbimazole is associated with congenital defects, including aplasia cutis of the neonate, therefore propylthiouracil remains the drug of choice during the ﬁrst trimester of pregnancy.…

Pharmacokinetics

Onset

The effect of a dose of 100 mg begins to wane in 2 to 3 h; even a 500-mg dose is completely inhibitory for only 6 to 8 h.

Half-life

75 min

Protein binding

~75%

Metabolism

Normal in severe liver disease, normal in severe kidney disease.

Excretion

Drugs and metabolites appear largely in the urine.

Side effects

Common

AstheniaDizzinessHeadacheNauseaVomitingmild urticarial papular rashpain and stiffness in the jointsparesthesiasskin pigmentationloss of hairg.i. intoleranceskin rashesjoint painhypothyroidism (due to overtreatment)goiter (due to overtreatment)

Serious

Chills
Diarrhoea
Feeling hot
Fever
Flushing
Hypersensitivity
Influenza
Influenza like illness
Pain
Paraesthesia
Pulmonary reaction
Skin reactions
Taste altered
Atrial fibrillation
Hyperthyroidism
Arthralgia
Dyspnoea
Goitre
Hyperhidrosis
Myalgia
Neoplasm complications
Palpitations
Residual metastases enlarged
Stroke
Tremor
Hepatotoxicity
fulminant hepatic necrosis (rare, potentially devastating, estimated 1 in 10,000 adults or 1 in 2000 children)
agranulocytosis (0.1%-0.5% of patients)
drug fever
hepatitis
nephritis
vasculitis (antineutrophilic cytoplasmic antibodies reported in ~50% of patients)
hypoprothrombinemia
bleeding
embryopathy (first trimester exposure, especially defects not apparent at birth like in urinary collecting system)
agranulocytosis (1 in 500 to 1000 cases, mostly reversible)