Dexamethasone × Metformin

Dexamethasone stimulates gluconeogenesis and reduces tissue insulin sensitivity. The glycaemic effect is stronger than with prednisolone due to long half-life and high potency.

Return of thirst and polyuria, rising fasting glucose, fatigue. In type 2 diabetes, possible decompensation with HbA1c rise of 0.5–1.5%.

For short dexamethasone pulses (1–3 days, e.g. cerebral oedema or post-chemotherapy), no metformin adjustment needed — transient hyperglycaemia is tolerated. For long-term therapy, increase metformin or add long-acting insulin. Check glucose twice daily in the first week.