Syndrome of inappropriate antidiuretic hormone secretion
Syndrome of inappropriate antidiuretic hormone (SIADH) secretion can result in hyponatremia. Classes of medications that can cause SIADH include antidepressants, antipsychotics, anticonvulsants, cytotoxic agents, and pain medications.5 The class of drugs most commonly associated with SIADH is selective serotonin reuptake inhibitors, particularly citalopram.5 Among the antipsychotics, risperidone is most associated with hyponatremia. The proposed mechanism of medication-induced SIADH is an increase in the release of ADH.6 Treatment options include discontinuing the offending medication(s) or switching to a different medication.
Hyponatremia is a rare adverse effect of lurasidone, with a reported incidence <1%.7 Although hyponatremia is potentially life-threatening, there is no recommendation to routinely monitor sodium levels in patients treated with lurasidone or other psychotropics, and patients who are prescribed lurasidone are not routinely monitored for sodium deficiency. Table 38,9 outlines risk factors for developing hyponatremia among patients taking psychotropic medications.
Mrs. G had been taking lurasidone for a few years and experienced fluctuating sodium levels. She had been taking divalproex, which by itself could cause hyponatremia and could have added to the effects of lurasidone in lowering sodium levels. Escitalopram briefly made her hyponatremia worse. Given Mrs. G’s medical illnesses, our focus had been on her underlying medical conditions rather than on a suspected medication-induced adverse effect.
In summary, patients who are prescribed lurasidone may benefit from regular monitoring of sodium levels. Monitoring sodium levels in geriatric patients who have multiple comorbid medical conditions and take multiple medications may reduce the morbidity and mortality associated with SIADH.