Antidiuretic hormone (ADH) is secreted by the posterior pituitary gland. Unsuppressed release of ADH
leads to hyponatremia. This condition is referred to as syndrome of inappropriate antidiuretic hormone
secretion (SIADH). Here we present the first case report of cefdinir-induced SIADH. A 76 year-old male
was prescribed cefdinir for a urinary tract infection. Two days later he fell and sustained a fracture of
C1, his sodium was notably 128 mmol/L. Seven days later he presented again to the emergency room
with generalized weakness, headaches, and decreased appetite and was found to have a sodium level of
116 mmol/L. Serum osmolality was appropriately decreased at 243 mOsmol/kg, urine osmolality was
not maximally dilute at 422 mOsmol/kg, and urine sodium was 94 mmol/L. On presentation, cefdinir
was held and he received ceftriaxone for the first 48 hours of his admission, after which this was
also stopped. He was treated with urea powder and received one dose of tolvaptan with progressive
improvement in sodium levels allowing for discharge. On post exposure day 27 serum sodium level
normalized (142 mmol/L), without the need for urea powder and all symptoms resolved.
This is the first reported case of SIADH associated with cefdinir though there have been scant case
reports [1] of cephalosporins causing SIADH.
