Lithium × Losartan

Drugs that block the renin-angiotensin system increase steady-state serum lithium concentrations (US lithium label, FDA). Reversible rises in lithium levels and lithium toxicity have been reported with angiotensin-converting enzyme inhibitors and, very rarely, with angiotensin II receptor blockers such as losartan (losartan SmPC). Lithium has a narrow therapeutic range: toxic concentrations are close to therapeutic ones (US lithium label).

Tremor, muscle twitching, nausea, vomiting, diarrhoea, poor coordination and confusion; severe cases progress to seizures and coma. Toxicity is expected at serum lithium concentrations of about 1.5 mmol/L and above, but some patients develop it at lower levels, including within the therapeutic range.

The Spanish losartan SmPC advises combining it with lithium with caution and only if the combination is essential; in that case, monitor lithium levels throughout co-administration (losartan SmPC). When losartan is started, stopped or its dose is changed, measure lithium more often, moving to weekly checks (lithium SmPC), and reduce the lithium dose according to levels and clinical response if needed (US lithium label, FDA). Take the lithium sample 12 hours after the last dose (lithium SmPC). The UK National Institute for Health and Care Excellence (NICE) advises taking any start or change of an angiotensin II receptor blocker into account when reviewing lithium levels and seeking specialist advice if in doubt (NICE NG222). Warn the patient about signs of lithium toxicity: diarrhoea, vomiting, coarse tremor, poor coordination, confusion and seizures (NICE NG222).