16th May 2025

Lithium

Lithium is a mood stabiliser often used in the management of bipolar disorder, the mechanism of which is not fully understood. It exists as two salts, lithium carbonate and lithium citrate, which are not dose equivalent. For this reason, it is important to ensure that lithium is prescribed by brand.

When initiating treatment, levels are normally measured one week after starting, one week after any dose change, and every week until levels are stable. Lithium levels should be taken 12 hours post dose and once levels are stable it is usually monitored every three months. The target for someone newly initiated on lithium should be between 0.6-0.8mmol/L. Higher serum levels of 0.8-1mmol/L may be desired in those who have relapsed whilst on treatment or who continue to have symptoms with functional impairment whilst on lithium. Alongside drug levels it is advised to monitor body mass index (BMI), urea and electrolytes, estimated glomerular filtration rate (eGFR), calcium, and thyroid function every 6 months.

An important reason for monitoring plasma lithium levels is the risk of lithium toxicity. Lithium toxicity may occur at normal serum levels, but it tends to occur at levels greater than 1.5mmol/L, and severe toxicity may occur at levels greater than 2mmol/L. Signs of lithium toxicity can be stratified into mild, moderate, and severe:

• Mild toxicity: Nausea, vomiting, diarrhoea, tremor, fatigue, light headedness, muscular weakness, and drowsiness.
• Moderate toxicity: Confusion, agitation, hypertonia, myoclonic jerks, choreoathetoid movements, urinary or faecal incontinence, and hypernatraemia.
• Severe toxicity: Coma, seizures, cerebellar signs, hypotension, and cardiac dysrhythmias 

There is no antidote for lithium toxicity. In the event of lithium toxicity, the medication should be discontinued, and supportive treatment should be given. For further information on the management of lithium toxicity please refer to the ‘Poisoning, emergency treatment’ summary in the BNF.