Lithium is cleared almost entirely by the kidneys and reabsorbed alongside sodium. Anything that reduces renal sodium excretion or glomerular filtration raises lithium levels. Thiazide diuretics, ACE inhibitors, angiotensin receptor blockers and NSAIDs are the classic culprits; dehydration, vomiting, diarrhoea and low-salt diets do the same.
Toxicity can develop at levels that were previously stable. A new interacting prescription, an intercurrent illness or a declining eGFR should prompt a level check within about a week, or sooner if symptoms appear.
- Check lithium level within about a week of starting a thiazide, ACE inhibitor, ARB or NSAID.
- Advise patients to seek advice during vomiting, diarrhoea or fever.
- Avoid regular NSAIDs in patients on lithium where possible.
- Monitor eGFR, thyroid function and calcium at least every six months.
- Recognise tremor, ataxia, confusion and diarrhoea as possible toxicity.
Why it matters
Most lithium toxicity follows a prescription or illness that someone could have anticipated.
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