Lithium levels are measured about 12 hours after the last dose; a random level is hard to interpret. Because lithium is cleared by the kidney and handled like sodium, anything that reduces renal clearance or causes sodium loss raises the level.
The three classes that most often do this are NSAIDs, ACE inhibitors or angiotensin receptor blockers, and thiazide diuretics. Dehydration, vomiting or diarrhoea do the same. Thyroid function, renal function and calcium need regular checks during long-term treatment.
- Take lithium levels 12 hours after the last dose.
- Recheck the level after starting an NSAID, ACE inhibitor, ARB or thiazide.
- Advise patients to hold lithium and seek advice during vomiting, diarrhoea or poor fluid intake.
- Monitor thyroid, renal function and calcium during long-term therapy.
Why it matters
Most lithium toxicity follows a predictable interaction or dehydration that a prescriber could have anticipated.
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