Name of the Thyroid Inhibitors Drugs that Inhibit hormones synthesis
- Propylthiouracil
- Methimazole
- Carbimazole
1.Propylthiouracil
| Propylthiouracil |
| Availability Tablets: 50 mg |
| Indications and dosages ➣ Hyperthyroidism Adults: Initially, 300 to 450 mg P.O. daily in equally divided doses q 8 hours; for maintenance, 100 to 150 mg P.O. daily. ➣ Thyrotoxic crisis Adults: 200 mg P.O. q 4 to 6 hours during first 24 hours, then a maintenance dosage of 100 to 150 mg P.O. daily |
Mechanism of Action
Inhibits synthesis of thyroid hormone by blocking oxidation of iodine in thyroid gland; blocks synthesis of T4 and T3
Pharmacokinetics
- Absorption: 75%
- Half-life elimination: 1-2 hr, increase in ESRD
- Protein Bound: 80-85%
- Peak plasma time: 1-2 hrL
- Metabolism: liver, to glucuronide conjugates, inorganic sulfates, sulfur metabolites
- Total body clearance: 7 L/hr
- Excretion: Urine (35%)
Administration
- Give with meals to reduce GI upset.
- Be aware that drug shouldn’t be used in children unless patient is allergic to or intolerant of methimazole, and there are no other treatment options available
Contraindications
- Hypersensitivity to drug
Precautions:
- Decreased bone marrow reserve
- Pregnancy and breastfeeding patients
- Children.
Adverse reactions
- CNS: drowsiness, headache, vertigo, neuritis, paresthesia
- GI: nausea, vomiting, diarrhea, epigastric distress
- Hematologic: agranulocytosis, leukopenia, thrombocytopenia
- Hepatic: jaundice, hepatic necrosis, liver failure
- Metabolic: hypothyroidism
- Musculoskeletal: joint pain, myalgia
- Skin: rash, urticaria, pruritus, skin discoloration, alopecia, cutaneous vasculitis
- Other: taste loss, fever, lymphadenopathy, parotitis, edema
Patient monitoring
- Monitor CBC and liver and thyroid function tests.
- Assess for signs and symptoms of hypothyroidism (cold intolerance, nonpitting edema, fatigue, weight gain, and depression).
- Monitor for severe rash, fever, jaundice, or enlarged cervical lymph nodes. If present, stop therapy and notify prescriber.
Patient teaching
- Instruct patient to take with meals to reduce GI upset.
- Teach patient to recognize and report signs and symptoms of hypothyroidism and jaundice.
- Advise patient to discuss iodine intake (as in iodized salt and shellfish) with prescriber.
- Tell patient to avoid over-the-counter cold remedies that contain iodine.
- Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
- Advise female patient of childbearing age to discuss pregnancy or breastfeeding with prescriber before taking.
- As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.
2.Methimazole
| Methimazole |
| Availability Tablets: 5 mg, 10 mg |
| Indications and dosages ➣ Mild hyperthyroidism Adults and adolescents: Initially, 15 mg P.O. daily in three equally divided doses at approximately 8-hour intervals. For maintenance, 5 to 15 mg/day in equally divided doses at approximately 8-hour intervals. Children: Initially, 0.4 mg/kg/day in three divided doses at 8-hour intervals. For maintenance, approximately 0.2 mg/kg/day in three divided doses at 8-hour intervals. ➣ Moderate hyperthyroidism Adults and adolescents: Initially, 30 to 40 mg P.O. daily in three equally divided doses at approximately 8-hour intervals. For maintenance, 5 to 15 mg/ day in three equally divided doses at approximately 8-hour intervals. Children: 0.4 mg/kg/day P.O. as a single dose or in divided doses at 8-hour intervals. For maintenance, approximately 0.2 mg/kg/day as a single dose or in three divided doses at 8-hour intervals. ➣ Severe hyperthyroidism Adults and adolescents: Initially, 60 mg/day P.O. in three equally divided doses at approximately 8-hour intervals. For maintenance, 5 to 15 mg/day in three equally divided doses at approximately 8-hour intervals. Children: Initially, 0.4 mg/kg/day P.O. as a single dose or in three divided doses at 8-hour intervals. For maintenance, approximately 0.2 mg/kg/day as a single dose or in three divided doses at 8-hour intervals |
Mechanism of Action
Inhibits synthesis of thyroid hormone by blocking oxidation of iodine in thyroid gland; blocks synthesis of thyroxine (T4) and triiodothyronine (T3)
Pharmacokinetics
- Bioavailability: 80-95%
- Peak plasma time: 1-2 hr
- Protein bound: None
- Metabolized by liver
- Half-life: 4-6 hr
- Excretion: Urine
Administration
- Give with meals as needed to reduce GI upset.
Contraindications
- Hypersensitivity to drug
- Breastfeeding
Precautions:
- Bone marrow depression
- Patients older than age 40
- Pregnant patients.
Adverse reactions
- CNS: headache, vertigo, paresthesia, neuritis, depression, neuropathy, CNS stimulation
- GI: nausea, vomiting, constipation, epigastric distress, ileus, salivary gland enlargement, dry mouth, anorexia
- GU: nephritis
- Hematologic: thrombocytopenia, agranulocytosis, leukopenia, aplastic anemia
- Hepatic: jaundice, hepatic dysfunction, hepatitis
- Metabolic: hypothyroidism
- Musculoskeletal: joint pain, myalgia
- Skin: rash, urticaria, skin discoloration, pruritus, erythema nodosum, exfoliative dermatitis, abnormal hair loss
- Other: fever, lymphadenopathy, lupuslike syndrome
Patient monitoring
- Check for agranulocytosis in patients older than age 40 and in those receiving more than 40 mg/day.
- Assess hematologic studies. Agranulocytosis usually occurs within first 2 months of therapy and is rare after 4 months.
- Monitor thyroid function tests periodically. Once hyperthyroidism is controlled, elevated thyroid-stimulating factor indicates need for dosage decrease.
- Assess liver function tests and check for signs and symptoms of hepatic dysfunction.
- Monitor patient for fever, sore throat, and other evidence of infection as well as for unusual bleeding or bruising.
- Assess patient for signs and symptoms of hypothyroidism, such as hard edema of subcutaneous tissue, drowsiness, slow mentation, dryness or loss of hair, decreased temperature, hoarseness, and muscle weakness.
Patient teaching
- Tell patient to take with meals if GI upset occurs.
- Advise patient to take exactly as prescribed to maintain constant blood level.
- Tell patient to report rash, fever, sore throat, unusual bleeding or bruising, headache, rash, yellowing of skin or eyes, abdominal pain, vomiting, or flulike symptoms.
- Caution female patient not to breastfeed while taking drug.
- As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above
3.Carbimazole
| Carbimazole |
| Availability Tablets: 5 mg, 20 mg; |
| Indications Thyrotoxicosis |
Mechanism of Action
Inhibits thyroid peroxidase and consequently synthesis of thyroid hormone.
Contraindications
- Previous history of adverse reactions to carbimazole or to any of the excipients in the composition.
- Retrosternal goitre.
- Serious pre-existing haematological conditions.
- To discuss with paediatric endocrinologist. Severe hepatic insufficiency.
- To discuss with paediatric endocrinologist.
Precautions
- Serum digitalis level may be increased when hyperthyroid patients on a stable digitalis glycoside regimen become euthyroid, reduce dose of digitalis glycoside if required.
- Metabolism of beta-adrenergic blockers may be increased in patients with hyperthyroidism, reduction in dosage of beta-blockers may be required when patients become euthyroid
Adverse reactions
- Leukopenia, agranulocytosis
- Pruritic rash, jaundice, acolic stools or dark urine, arthralgias, abdominal pain, fatigue, fever, or pharyngitis
REFERENCES
- Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
- McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
- April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
- Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
- Nursebro.com, Search – Nursebro
Stories are the threads that bind us; through them, we understand each other, grow, and heal.
JOHN NOORD
Connect with “Nurses Lab Editorial Team”
I hope you found this information helpful. Do you have any questions or comments? Kindly write in comments section. Subscribe the Blog with your email so you can stay updated on upcoming events and the latest articles.
