PH7.3 | PH7.3 | Thyroid Disorder Pharmacotherapy — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Thyroid Disorder Pharmacotherapy — Key Takeaways:

• Levothyroxine (T4): Standard hypothyroid replacement, 1.6 mcg/kg/day. Start low in elderly/cardiac (25 mcg). Take fasting — interactions with iron, calcium, antacids reduce absorption.
• Liothyronine (T3): Faster onset; used in myxoedema coma (IV) and where immediate T3 effect needed.
• Carbimazole vs PTU: Both inhibit TPO. PTU extra: blocks peripheral T4→T3 conversion. PTU preferred in 1st trimester pregnancy (switch to carbimazole in 2nd trimester — PTU hepatotoxicity risk). Carbimazole preferred otherwise.
• Agranulocytosis: Rarest but most serious ADR of thionamides — warn every patient; stop drug immediately on sore throat/fever.
• Lugol's iodine: Wolff-Chaikoff effect — transient organification block; pre-operative use for vascularity; in thyroid storm give AFTER PTU.
• Radioactive iodine (¹³¹I): Definitive treatment for non-pregnant adults with Graves', toxic nodule, toxic MNG. Contraindicated in pregnancy, breastfeeding, active severe ophthalmopathy.
• Thyroid storm: PTU + Lugol's (after PTU) + propranolol + hydrocortisone + treat precipitant.
• Propranolol: Symptom control only; also inhibits T4→T3 peripherally (high dose).

REFLECT

Imagine you are prescribing carbimazole to a 40-year-old with newly diagnosed Graves' disease. What are the two most important safety instructions you would give, and what is the rationale for each? Now consider: if she returns at 6 months, clinically euthyroid, and asks 'Can I stop this tablet? Am I cured?' — how would you counsel her? Write a brief patient-centred explanation of why relapse rates are 30–40%, what the options are (continue for 12–18 months total vs radioiodine vs surgery), and how shared decision-making applies in this scenario.