Newly diagnosed hypothyroidism in an elderly patient with ischaemic heart disease: treatment considerations

A 78-year-old woman is reviewed in the outpatient clinic. She reports progressive fatigue, weight gain of 4 kg over three months, cold intolerance, and constipation. She has a history of ischaemic heart disease with a myocardial infarction two years ago. Examination: heart rate 52 bpm, blood pressure 138/78 mmHg, dry skin, slow-relaxing ankle reflexes, and a small goitre. Blood tests: TSH 12.6 mIU/L (0.4-4.0), free T4 9.0 pmol/L (9.0-19.0), anti-thyroid peroxidase antibodies positive. She takes bisoprolol 2.5 mg daily, atorvastatin 20 mg at night, aspirin 75 mg daily, ferrous sulfate 200 mg daily, and calcium carbonate 500 mg twice daily. She has no drug allergies. Weight 68 kg. She is not pregnant. Diagnosis: primary hypothyroidism. Task: Prescribe appropriate therapy. State the starting dose, any specific administration instructions in relation to her other tablets, and when to recheck thyroid function.