Adverse reactions

Editor – I read with interest ‘Lesson of the month 1: A rare adverse reaction between flucloxacillin and paracetamol’, published in March's Clinical Medicine, and write with a similar case seen recently in our institution, to further highlight this issue. In addition, although the diagnostic test of choice (urinary organic acids) was unavailable locally we were able to confirm the diagnosis by liaising with another hospital laboratory within our region.

An 80-year-old patient with left leg cellulitis and a non-drainable calf abscess, requiring a 3-week course of intravenous flucloxacillin, developed marked hypokalaemia and was found to have a severe, high anion-gap metabolic acidosis (pH 7.16, bicarbonate 7.4 mmol/L, base excess -22.4 mmol/L, serum anion gap 30 mmol/L), without acute kidney injury. Pyroglutamic acidosis was suspected and flucloxacillin and paracetamol were discontinued, and N-acetylcysteine was administered. The acidosis resolved over the course of several days. Urinary organic acid testing was performed at another hospital in the region, showing grossly increased levels of pyroglutamic acid, which had resolved when a repeat specimen was sent 9 days later.