The Poison Review

Extreme γ-Butyrolactone Overdose With Severe Metabolic Acidosis Requiring Hemodialysis. Roberts DM et al. Ann Emerg Med 2011 March 22 [Epub ahead of print]

Abstract

The industrial chemical γ-butyrolactone (GBL) is rapidly metabolized into γ-hydroxybutyric acid (GHB). GBL or GHB overdose frequently causes transient decreased mental status and respiratory depression.  As a result, respiratory acidosis is commonly seen in association with these overdoses. However, concomitant significant metabolic acidosis has not been reported.

This very interesting case report, from New South Wales in Australia, describes a 39-year-old man who presented after a massive overdose of GBL, and had what the authors claim is the highest GHB level ever reported in a survivor (2,498 mg/L).  His initial blood gas (after intubation) was ph 6.75, pCO2 70 mm HG, pO2 483 mm Hg, and lactate 2.9 mEq/L, consistent with severe combined respiratory and metabolic acidosis.  Methanol, ethylene glycol, and propylene glycol were not detected. The authors hypothesize that in massive overdose, GHB (pKa 4.72) rapidly dissociates to a hydrogen ion and the anion, causing acidosis. Since the lactate level was relatively low, lactic acidosis could not explain the acid-base disturbance seen in this case. Testing confirmed that the liquid the patient consumed was in fact GBL.

Despite a difficult course in hospital, the patient improved after continuous venovenous hemodiafiltration (CVVHD) was started, and was discharged after he “recovered well” and was evaluated by the psychiatric service.