A 61-year-old man presents to the Emergency Department with vomiting, abdominal discomfort and reduced oral intake after a diarrhoeal illness. He looks dehydrated and is breathing slightly deeper than usual. He has type 2 diabetes .Observations: temperature 37.4°C, heart rate 104/min, blood pressure 108/68 mmHg, respiratory rate 22/min, oxygen saturation 98% on air. Capillary glucose is 10.5 mmol/L. Venous gas shows pH 7.30, bicarbonate 17 mmol/L, lactate 1.9 mmol/L and blood ketones 3.9 mmol/L.

Which medication is most likely to have contributed to this presentation? Select only one best single option.