Thyroid Hormone Replacement Therapy Quiz

Thyroid Hormone Replacement

• Triiodothyronine (T3) has a shorter half-life compared to thyroxine (T4).
• The standard dose range for L-thyroxine (LEVOTHYROXINE) tablets is 50-200 mcg/day.
• L-thyroxine is cautioned in elderly patients with known ischaemic heart disease.
• Triiodothyronine (T3) is used intravenously for myxoedema coma.

Absorption and Half-Life of L-Thyroxine

• Factors that can reduce the absorption of L-thyroxine include iron, calcium, and soy products.
• The half-life of L-thyroxine is 1-2 days.
• Symptoms of hypothyroidism improve within 1-2 weeks after starting L-thyroxine treatment.

Special Situations and Interactions

• The dose of L-thyroxine may need to be adjusted in special situations such as pregnancy, lactation, and cardiac disease.
• Medications that can accelerate the metabolism of L-thyroxine and Liothyronine include phenytoin, carbamazepine, and rifampin.
• Medications that can potentiate the effects of L-thyroxine and Liothyronine include warfarin and insulin.
• The recommended treatment for overdose of L-thyroxine and Liothyronine is supportive care.

Congenital Hypothyroidism and Iodine Intake

• Cretenism is characterized by mental retardation, growth restriction, and spastic diplegia.
• The cause of endemic goiter is iodine deficiency.
• The prevalence of sporadic congenital hypothyroidism is 1 in 3,000-4,000 births.
• The primary source of iodine intake is iodized salt.
• The recommended daily intake of iodine according to WHO is 150 mcg/day.
• A higher intake of iodine is required in pregnancy and lactation.

Anti-Thyroid Drugs

• Thionamides, such as methimazole and carbimazole, inhibit iodide uptake into the thyroid gland follicular cell.
• Thionamides also inhibit organification and hormone release, and peripheral thyroid hormone metabolism.
• The mechanism of action of thionamides is the inhibition of thyroid hormone synthesis.
• The clinical use of thionamides is in the treatment of hyperthyroidism.
• The maximum effect of thionamides is seen after 1-2 weeks of treatment.
• Methimazole has a shorter half-life compared to carbimazole.
• Carbimazole is preferred during pregnancy.
• Methimazole has an additional pharmacological property of inhibiting peripheral T4 to T3 conversion.
• Carbimazole accumulates in the thyroid and is primarily metabolized in the thyroid and elsewhere.
• The most serious side effect of thionamides is agranulocytosis.
• Common side effects of thionamides include rash, pruritus, and arthralgia.
• Neutropenia and agranulocytosis caused by thionamides should be managed with prompt withdrawal of the drug and supportive care.

Radioactive Iodine

• Radioactive iodine is used in the treatment of nodular thyrotoxicosis.
• The half-life of radioactive iodine is 8 days.
• Radioactive iodine destroys thyroid follicles, reducing thyroid hormone production.
• The risk of hypothyroidism after treatment with radioactive iodine is high.

Iodide's Effects on Thyroid Hormone Synthesis and Secretion

• Iodide inhibits the conversion of iodide to organic iodine, reducing thyroid hormone synthesis.
• High doses of iodide inhibit thyroid hormone release.
• Iodide decreases the vascularity of the thyroid gland.

Propranolol

• The main mechanism of action of Propranolol is the blockade of beta-adrenoceptors.
• The primary use of Propranolol is in the treatment of thyrotoxic crisis.
• Propranolol has a short half-life of 3-6 hours.
• Propranolol can aggravate bronchial asthma due to its action on bronchial B2-receptors.
• The main adverse effect of Propranolol is bradycardia.
• Contraindications for the use of Propranolol include heart failure and asthma.

Cardioselective Beta-Adrenoceptor Blockers

• Cardioselective beta-adrenoceptor blockers have a higher affinity for beta1-receptors.
• Cardioselective beta-adrenoceptor blockers do not cause bronchospasm.
• Indications for the use of cardioselective beta-adrenoceptor blockers include hypertension, angina, and heart failure.