lithium and furosemide

Furosemide, a loop diuretic, causes sodium and volume depletion. This increases proximal tubular reabsorption of lithium, compensating for the diuretic-induced sodium loss. As a result, lithium renal clearance decreases, leading to elevated serum lithium concentrations.

Serum lithium levels can rise significantly, potentially causing lithium toxicity. Symptoms include nausea, vomiting, diarrhoea, tremor, confusion, ataxia, and in severe cases, seizures or coma. The risk is higher in patients with dehydration or those on a low-sodium diet.

Advise the patient to maintain adequate fluid and sodium intake. Avoid thiazides if possible, as they reduce lithium clearance even more than loop diuretics; if an alternative diuretic is needed, use one with minimal effect on lithium handling and monitor levels closely.

This interaction is well established and documented in multiple references, including the British National Formulary and product labels for lithium. Clinical studies and case reports consistently demonstrate that loop diuretics reduce lithium clearance and increase serum lithium concentrations.