An Unusual Case of 5-Oxoproline Acidosis.

Although metabolic acidosis is a common phenomenon, its differential diagnoses include a variety of rare conditions. Among the causes of high anion gap metabolic acidosis is an accumulation of 5-oxoproline or pyroglutamic acid. It is commonly understood that development can occur in the context of high-dose paracetamol intake and either relevant clinical risk factors or comedication with flucloxacillin or oxacillin. As a rare condition, it has become well-known only to specialized clinicians. We reported a case of high anion gap metabolic acidosis caused by 5-oxoproline in a middle-aged male treated only with high-dose flucloxacillin. Our patient had neither a history of paracetamol use nor classical risk factors to a degree, making the development of 5-oxoproline/pyroglutamic acidosis plausible. Although there have been plenty of case reports of this condition because of the coadministration of paracetamol/acetaminophen and flucloxacillin/oxacillin, to our knowledge, this is only the second published case of 5-oxoproline acidosis without paracetamol use, making it either highly unusual or potentially underdiagnosed. Therefore, we suggest considering 5-oxoproline/pyroglutamic acidosis when evaluating the etiology of metabolic acidosis in patients on high-dose flucloxacillin/oxacillin, even without a history of concomitant or previous paracetamol exposure or other classical risk factors.