[Lithium intoxication due to simultaneous use of trimethoprim]

A 40-year-old woman with a schizoaffective disorder was, inter alia, receiving lithium carbonate. During a simultaneous treatment with trimethoprim, she experienced symptoms of nausea, a feeling of malaise, concentration problems, trembling, an uncertain gait, diarrhoea and muscle spasms, without fever. The lithium level appeared to be elevated. The only cause of the intoxication indicated was the simultaneous use of trimethoprim. Following clinical rehydration, the patient made a good recovery. Trimethoprim has the same effect on the kidney as amiloride, a potassium-sparing diuretic, for which it is known that its combined use with lithium can result in an elevated lithium level.