Lithium has a narrow therapeutic range, so the timing of the sample matters. The usual standard is a trough level about twelve hours after the last dose, taken at steady state, which is around five days after a dose change.
Check renal and thyroid function at baseline and regularly, and review interacting drugs: non-steroidal anti-inflammatory drugs, ACE inhibitors, thiazides and dehydration all raise levels. Toxicity can appear as tremor, vomiting, diarrhoea or confusion.
- Draw trough levels about 12 hours post-dose, at steady state.
- Recheck about five days after any dose change.
- Review NSAIDs, ACE inhibitors, ARBs and thiazides before co-prescribing.
- Advise stopping and seeking review if vomiting, diarrhoea or confusion develops.
Why it matters
A wrongly timed sample can mislead dosing in a drug with little margin for error.
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