Hyperthyroidism

Source: SGH endocrine update 2026

Anti-thyroid Drugs (ATDs)

• Carbimazole (CMZ)
• Thiamazole (TMZ)
• Propylthiouracil (PTU)

Pregnancy to check before starting ATD, contraception advice, pregnancies must be planned.

Dose conversion

• CMZ 15mg - TMZ 10mg
• CMA 10mg - PTU 100mg

Conventionally given for 12-18 months course

Minor SEs

There is no guidelines for routine monitoring, can consider, FBC, LFT

Pruritus, Rash/Urticaria, Arthralgia/Arthritis

• Minor cutaneous reactions: Common – occurs in 5-25% of patients

Pre-empt your patients

• Stop ATD if severe reaction, including angioedema, anaphylaxis

Rare, serious SEs

• Hepatotoxicity (0.1-0.3%): CMZ associated with cholestasis, Higher risk of fulminant hepatitis with PTU
• Agranulocytosis (~0.1%): ANC < 0.5 x 10^9 /L
• ANCA+ Vasculitis (annual incidence <0.01%): a/w longer duration of ATDs, high risk w PTU
• Teratogenicity: PTU (1%): Less severe, CMZ (2%): More severe

Smoking & Graves’ Disease

Counsel patients for smoking cessation

Smoking is associated with higher risk of:

• Graves'
• High TRAb levels at diagnosis
• Relapse after conventional course of ATDs
• Graves’ Ophthalmopathy (GO)
• More severe stages of GO
• New development / worsening of GO after RAI

Conventional ATD Therapy

• ATD can be stopped after 12-18 months of treatment if TFT and TRAb are normal
• Patients should be on low dose of ATD (eg CMZ <5mg OM) prior to discontinuation
• Risk factors for relapse after discontinuation?
  • Positive TRAb at discontinuation
  • Male
  • Smoker
  • Large goitre
  • Severe GO
  • <20
  • >60