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Thyroid Blocking Agent / Pre-operative Thyroid Preparation Pregnancy: Use only in radiation emergency (benefit outweighs risk); short-course pre-operative use acceptable. Prolonged use causes fetal hypothyroidism and goitre — avoid.

Potassium Iodide / Lugol's Solution

Brand names: Lugol's Iodine Solution (potassium iodide 10% + iodine 5%)

Adult dose

Dose: Pre-operative preparation for thyroidectomy: Lugol's solution 0.1–0.3 mL TDS (approximately 5–7 drops TDS) for 10–14 days before surgery. Thyroid storm: 500mg potassium iodide orally (or Lugol's 1mL in water) every 8–12h — given at least 1 hour AFTER antithyroid drug (propylthiouracil or carbimazole). Radiation emergency: potassium iodide 130mg as single dose.
Route: Oral (well diluted in water, milk, or juice)
Frequency: Three times daily (pre-op); every 8–12 hours (thyroid storm); single dose (radiation emergency)
Max: Individualised per indication — do not use long-term
Wolff-Chaikoff effect: high iodide temporarily inhibits thyroid hormone synthesis. Must give antithyroid drug FIRST in thyroid storm — if iodide given first, it provides substrate for further hormone synthesis. Short-term use only — thyroid 'escapes' from blockade after 10–14 days.

Paediatric dose

Route: Oral
Frequency: As per indication
Max: Radiation emergency: <1 month: 16mg; 1 month–3 years: 32mg; 3–12 years: 65mg; 12–18 years: 130mg
BNFc: Radiation emergency doses by age as above. Pre-operative and thyroid storm use: seek specialist paediatric endocrinology opinion.

Dose adjustments

Renal

Use with caution in renal impairment — iodide accumulation risk; monitor thyroid function.

Hepatic

No specific adjustment — use with caution.

Clinical pearls

  • In thyroid storm: sequence is critical — BLOCK (PTU/carbimazole) → IODIDE (minimum 1h later) → BETA-BLOCKER → CORTICOSTEROIDS → TREAT PRECIPITANT
  • Lugol's solution is not standardised commercially — concentration must be verified; prescribe as potassium iodide mg dose where possible
  • Wolff-Chaikoff effect lasts only 10–14 days — do not use iodide as sole long-term treatment for hyperthyroidism
  • Radiation emergency protocols (nuclear accident): WHO recommends potassium iodide tablets as thyroid blocking agent — stockpiled by governments

Contraindications

  • Hypersensitivity to iodine
  • Dermatitis herpetiformis
  • Hypocomplementaemic vasculitis
  • Do not use long-term (thyroid escape occurs)

Side effects

  • Metallic taste
  • Salivation increase
  • GI upset
  • Hypothyroidism (prolonged use)
  • Iodism (prolonged use: rhinorrhoea, lacrimation, acneiform rash)
  • Hypersensitivity reactions

Interactions

  • Antithyroid drugs (carbimazole/PTU) — must be given before iodide in thyroid storm
  • Lithium — additive goitrogenic effect
  • ACE inhibitors, potassium-sparing diuretics — hyperkalaemia risk (potassium content)

Monitoring

  • TFTs during use
  • Potassium (hyperkalemia risk)
  • Clinical signs of iodism

Reference: BNFc; BNF 90; BTA Guidelines on Thyroid Storm; WHO Radiation Emergency Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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