CARBIMAZOLE tablets 5mg, 20mg

Dose: The initial dose can range from 5 to 40mg daily depending on the degree of hyperthyroidism, with repeat thyroid function usually after 4 weeks. The dose may then be progressively reduced to the lowest dose to maintain thyroid function within range. If unclear which dose to initiate, endocrinology can advise on receipt of referral, or seperately via Clinical Dialogue. Please note that propylthiouracil is the antithyroid drug of choice in the first trimester of pregnancy.

See Highland Formulary: Antithyroid drugs

Levothyroxine

Levothyroxine (T4) should be initiated once daily at a dose of 0.8 to 1.6 micrograms/kg, which is usually 50 to 125 micrograms. A lower dose should be used for elderly patients and patients with cardiac disease. It must be taken on an empty stomach, with no food consumption for 30 minutes. Not taking it in this way may prevent optimised treatment.

The aims of treatment are to manage the patient's hypothyroid symptoms and maintain thyroid stimulating hormone (TSH) levels within the normal range. If the TSH levels are too low then there is an increased risk of developing atrial fibrillation and osteoporosis. If the aims of treatment are not achieved with levothyroxine then the following should be checked:

• Is the dose correct for the weight of the patient?
• Is the treatment being taken correctly on an empty stomach?
• Are there other treatments that might impair absorption (antacids, proton pump inhibitors, histamine-2-receptor antagonists)?
• Are there other undiagnosed endocrine or auto-immune conditions?
• Are there other causes of fatigue (depression, fibromyalgia, etc)?

These factors should be taken into account for any patient being considered for liothyronine (T3) treatment and when reviewing existing patients. Liothyronine must only be initiated by an endocrinologist. 

Further information is available from the British Thyroid Association – Management of Primary Hypothyroidism & FAQs for GPs