Pattern of lithium exposure predicts poisoning severity: evaluation of referrals to a regional poisons unit

BACKGROUND: Lithium toxicity may result in severe clinical features. There is on-going uncertainty about the significance of serum lithium concentrations in patients with lithium toxicity. AIM: To examine potential relationships between stated quantity of lithium ingested, serum lithium concentrations, and poisoning severity among patients referred to a regional poisons centre. METHODS: Prospective evaluation of enquiries to the Scottish Poisons Information Bureau about lithium toxicity between 2000-2005 inclusive. RESULTS: There were 172 enquiries, relating to acute ingestion (n = 101), acute-on-therapeutic ingestion (n = 38), or chronic poisoning (n = 33). Poisoning severity was moderate or severe in 9.9%, 26.3% (p < 0.05 vs. acute) and 54.5% (p < 0.005 vs. acute) of each group, respectively. Median (IQR) serum lithium concentrations in each group were: 2.4 (1.7-3.3) mmol/l, 2.1 (1.4-3.8) mmol/l, and 2.3 (1.9-3.3) mmol/l, respectively. The median stated quantities ingested in acute and acute-on-therapeutic lithium exposure were 5000 mg (2000-11 050 mg) and 4000 mg (2400-8820 mg), respectively. DISCUSSION: Patients with acute-on-therapeutic and chronic poisoning are at greatest risk of severe toxicity. These differences cannot be explained by either the quantity of lithium ingested or serum lithium concentration alone.