In an adult patient taking low‑dose lithium 150 mg at bedtime for mood stabilization, is concomitant use of losartan (an angiotensin II receptor blocker) contraindicated?

Low-Dose Lithium with Losartan: Not Contraindicated, But Requires Monitoring

Low-dose lithium 150 mg at bedtime is NOT contraindicated with losartan, but this combination requires careful monitoring of serum lithium levels and renal function due to the risk of lithium toxicity. 1

Key FDA Guidance

The FDA drug label for losartan explicitly addresses this interaction: "Increases in serum lithium concentrations and lithium toxicity have been reported during concomitant administration of lithium with angiotensin II receptor antagonists. Monitor serum lithium levels during concomitant use." 1 This is a monitoring requirement, not a contraindication. The only absolute contraindication for losartan is coadministration with aliskiren in diabetic patients. 1

Mechanism and Clinical Risk

Losartan and other ARBs can impair renal lithium clearance, potentially increasing serum lithium concentrations by reducing glomerular filtration or altering tubular handling. 2, 3 This interaction has been documented in case reports, including a 62-year-old woman who developed chronic lithium toxicity (loose stools, weakness, slurred speech, tremors, dystonia) after telmisartan (another ARB) was added to her long-standing lithium regimen. 4

However, the evidence is nuanced: One animal study found that losartan specifically did NOT modify renal lithium handling in rats, suggesting the interaction may be less pronounced with losartan compared to other ARBs or ACE inhibitors. 5 Despite this, clinical caution remains warranted given human case reports with ARBs as a class.

Practical Management Algorithm

When combining low-dose lithium with losartan:

1. Obtain baseline serum lithium level before starting losartan (or within days of initiation)
2. Recheck lithium level within 1-2 weeks after losartan initiation or dose changes
3. Monitor renal function (creatinine, eGFR) concurrently 1
4. Continue periodic monitoring (every 3-6 months at minimum) once stable
5. Watch for clinical signs of lithium toxicity: tremor, confusion, slurred speech, weakness, gastrointestinal symptoms, ataxia 4
6. Adjust lithium dose downward if levels rise above therapeutic range (typically 0.6-1.2 mEq/L for mood stabilization, though lower levels may suffice for some indications) 6

Important Caveats

• Elderly patients are at higher risk due to age-related decline in renal function 4, 2
• Volume depletion (from diuretics, diarrhea, reduced fluid intake) amplifies the risk 1
• Concomitant NSAIDs further increase lithium levels and should be avoided when possible 1, 2
• The 150 mg dose is relatively low, which may reduce (but not eliminate) toxicity risk compared to standard therapeutic doses

The combination is manageable with appropriate monitoring—this is standard practice for lithium therapy with any medication affecting renal function. 2, 3