lithium and naproxen

Pharmacokinetic interaction. Naproxen inhibits renal prostaglandin synthesis, which reduces renal blood flow and glomerular filtration rate. This decreases renal clearance of lithium, leading to increased serum lithium concentrations.

Elevated lithium levels can cause lithium toxicity, presenting with nausea, vomiting, coarse tremor, ataxia, confusion, seizures, and potentially renal impairment, cardiac arrhythmias, or death. The risk is higher in patients with pre-existing renal dysfunction, dehydration, or concurrent use of diuretics.

Avoid co-prescription if possible; consider alternative analgesics such as paracetamol or aspirin. If combined treatment is necessary, monitor serum lithium concentrations closely at baseline, after 3 to 5 days of starting naproxen, and weekly thereafter. Monitor for signs of lithium toxicity and adjust the lithium dose accordingly. Educate the patient about symptoms of toxicity.

Well-established interaction, supported by multiple case reports and clinical studies.