Oral Adjunct to radio-iodine therapy, Hyperthyroidism, Preparation for thyroidectomy
Adult: Initially, 300 mg daily in 3 equally divided doses with approx 8-hour intervals. For severe cases or very large goitres: Initially, 400 mg daily; 600-900 mg daily may be required in some cases. Maintenance (once euthyroid): 50-150 mg daily usually continued for 1-2 years. Adjust dose based on patient’s tolerability, clinical response and thyroid status. Child: 6-10 years 50-150 mg daily; >10 years 150-300 mg daily. Doses are given in 3 divided doses daily at approx 8-hour intervals.
Renal Impairment
GFR <10 mL/min: Reduce dose by 50%. GFR 10-50 mL/min: Reduce dose by 25%.
Hepatic Impairment
Dosage reduction may be needed.
Administration
Should be taken with food.
Special Precautions
Patient undergoing surgery. Hepatic and renal impairment. Children. Pregnancy and lactation.
Adverse Reactions
Significant: Bleeding, hypoprothrombinaemia, bone marrow suppression (e.g. aplastic anaemia, thrombocytopenia, leucopenia), exfoliative dermatitis, fever, hypothyroidism, lupus-like syndrome (e.g. splenomegaly), nephritis, glomerulonephritis, interstitial pneumonitis. Blood and lymphatic system disorders: Granulocytopenia, lymphadenopathy. Ear and labyrinth disorders: Hearing impairment. Gastrointestinal disorders: Ageusia, abdominal pain, nausea, vomiting. General disorders and administration site conditions: Oedema. Hepatobiliary disorders: Jaundice, hepatitis. Immune system disorders: Erythema nodosum, urticaria. Investigations: Increased serum bilirubin, ALT/AST. Musculoskeletal and connective tissue disorders: Arthralgia, arthritis, myalgia, myopathy, periarteritis. Nervous system disorders: Drowsiness, headache, neuritis, paraesthesia, vertigo. Respiratory, thoracic and mediastinal disorders: Pulmonary alveolar haemorrhage. Skin and subcutaneous tissue disorders: Alopecia, pruritus, skin pigmentation, rash. Potentially Fatal: Severe liver injury, acute liver failure, agranulocytosis, vasculitis (e.g. leucocytoclastic). Rarely, serious skin reactions (e.g. Stevens-Johnson syndrome, toxic epidermal necrolysis).
Obtain CBC, LFTs (e.g. bilirubin, alkaline phosphatase, ALT and AST), thyroid function test (free serum T4, total serum T4, TSH, total serum T3) and prothrombin time (especially before surgery) prior initiating and during the course therapy. Monitor for signs and symptoms of illness or agranulocytosis (e.g. fever, sore throat, general malaise), liver injury (e.g. anorexia, dark urine, jaundice, fatigue, pruritus, right upper quadrant abdominal pain) during therapy.
Overdosage
Symptoms: Agranulocytosis, pancytopenia, epigastric distress, nausea, vomiting, fever, headache, arthralgia, hypothyroidism, oedema and pruritus. Management: Symptomatic and supportive treatment. Employ gastric lavage or induce emesis. Activated charcoal may be administered.
Drug Interactions
May potentiate the effect of oral anticoagulants (e.g. warfarin). Concomitant β-blockers, digoxin and theophylline may require dosage adjustments according to changes in patient’s thyroid status.
Action
Description: Propylthiouracil interferes with the catalyst thyroid peroxidase, therefore preventing iodine from being oxidised in the thyroid gland which results in diminished thyroid hormone synthesis. It also inhibits the formation of thyroglobulin by interfering with the coupling reaction of iodotyrosyl residues. Additionally, it blocks the peripheral deiodination of thyroxine to tri-iodothyronine. Pharmacokinetics: Absorption: Rapidly and readily absorbed from the gastrointestinal tract. Bioavailability: Approx 50-75%. Time to peak plasma concentration: Approx 1-2 hours. Distribution: Concentrated in the thyroid gland. Crosses the placenta and enters breast milk. Plasma protein binding: Approx 80-85%. Metabolism: Extensively metabolised in the liver via glucuronidation into glucuronic acid conjugate. Excretion: Via urine (approx 35%, primarily as metabolites). Elimination half-life: Approx 1-2 hours.
Chemical Structure
Propylthiouracil Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 657298, Propylthiouracil. https://pubchem.ncbi.nlm.nih.gov/compound/Propylthiouracil. Accessed Oct. 26, 2020.
H03BA02 - propylthiouracil ; Belongs to the class of thiouracils. Used in the management of thyroid diseases.
References
Anon. Propylthiouracil – Pregnancy and Lactation. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 05/10/2020.Anon. Propylthiouracil. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 05/10/2020.Anon. Propylthiouracil. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 05/10/2020.Buckingham R (ed). Propylthiouracil. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 05/10/2020.Joint Formulary Committee. Propylthiouracil. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 05/10/2020.Propylthiouracil 50mg Tablets (Drug Houses of Australia Pte Ltd.). National Pharmaceutical Regulatory Agency - Ministry of Health Malaysia. https://www.npra.gov.my/. Accessed 05/10/2020.Propylthiouracil 50mg Tablets (Renata [UK] Limited). MHRA. https://products.mhra.gov.uk/. Accessed 16/10/2020.Propylthiouracil Tablet (Actavis Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 05/10/2020.Propylthiouracil, PTU. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com/. Accessed 05/10/2020.
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