Lithium is cleared almost entirely by the kidney, and anything that makes the kidney hold on to sodium makes it hold on to lithium too. Non-steroidal anti-inflammatories, ACE inhibitors or angiotensin receptor blockers, and thiazide diuretics each raise serum lithium, sometimes into the toxic range within days. So do dehydration, diarrhoea and vomiting. The patient is often started on one of these by another doctor who does not know about the lithium.
- Ask every patient on lithium to tell any prescriber, including pharmacists, that they take it.
- Avoid NSAIDs; paracetamol is the safer analgesic for someone on lithium.
- If an ACE inhibitor, ARB or thiazide is started, check the lithium level within 5–7 days.
- Advise holding lithium and seeking review during vomiting, diarrhoea or poor fluid intake.
- Tremor that coarsens, new unsteadiness, confusion or vomiting means check a level the same day.
Why it matters
Most lithium toxicity follows a change made by someone else, so the patient has to be the one carrying the warning.
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