Ciprofloxacin × Metformin

Fluoroquinolones disturb glucose homeostasis — they can cause both hypoglycaemia (especially in older patients on glucose-lowering therapy) and hyperglycaemia. The mechanism involves pancreatic beta-cell effects.

Hypoglycaemia: sweating, tremor, hunger, confusion at glucose below 3.9 mmol/L. Hyperglycaemia: thirst, polyuria, fatigue.

For short ciprofloxacin courses (5–7 days) on metformin, intensify glucose self-monitoring (twice daily) for the first week. In older patients and diabetics on insulin or sulfonylureas, choose an alternative antibiotic (cephalosporin, amoxicillin-clavulanate).