Serotonin syndrome after lithium add-on medication to paroxetine

A 59-year-old female patient was hospitalized on account of a depressive episode in the course of a long-standing bipolar disorder. On a combination of lithium (400 mg/day) and paroxetine (30 mg/day) she developed symptoms of shivering, high-frequency tremor of the upper and lower limbs, skin flush in the face, agitation, and slight impairment of mental focusing, suggestive of a serotonin syndrome. At this stage serum lithium and paroxetine levels were 0.63 mmol/l, and 693 ng/ml, respectively; the latter was six times higher than the upper concentrations seen in patients on this dosage of the drug. Consequently, the dosage of paroxetine was reduced to 10 mg/day, and lithium was continued. This regimen resulted in a steady-state paroxetine serum level of 390 ng/ml. The patient became symptom-free and the depressive episode attenuated, thus enabling us to discharge the patient.