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 Metformin in CKD – sick day rules

Generally metformin use is questioned once eGFR falls to ~50ml/min and absolutely contra-indicated if eGFR falls below 30ml/min

During illness varying degrees of dehydration are common and thus effective eGFR can fall quite acutely making the continued use of metformin over these periods of illness hazardous in almost any patient but particularly those with CKD stage 3a (eGFR 45-60ml/min)

Advice therefore is that during episodes of illness (or if starving pre-op or pre-investigation) in such patients they should temporarily discontinue metformin 24-48 hours before and restart 36-48 hours after normal eating and drinking is re-commenced

Unsurprisingly for some of these patients the discontinuation will be associated with a blood glucose rise which may require alternative therapy (either planned concomitant increase of another agent or supplementary insulin) – in a first episode monitoring instructions should be given (pre meals and bed) and a contact plan for a trigger level of hyperglycaemia (greater than 14mmol/L) that would merit alternative therapy