MON-615 - Trimethoprim-Sulfamethoxazole Induced Endogenous Hyperinsulinemic Hypoglycemia with Concurrent SIADH-Like Hyponatremia in an Elderly Patient

Background:
TMP-SMX is commonly used, and its potential to cause severe disturbances of endocrine and electrolyte balances because of drug interactions is grossly underrated. Though rare cases of TMP-SMX-induced hypoglycemia and hyponatremia have been documented independently, their occurrence together with complete biochemical validation is rare.

Case:
An 82-year-old type 2 diabetic male with hypertension was brought in for developing acute lethargy. He was identified to have potentially life-threatening hypoglycemia (glucose: 35 mg/dL) and severe hypo-osmolar hyponatremia (serum Na Nadir: 98 mmol/L; serum osmolality: 224mOsm/kg). Patient was on low doses of glimepiride, metformin, hydrochlorothiazide and on first week of TAB/SMX therapy for urinary tract infection due to Klebsiella pneumoniae. During the critical sampling during hypoglycemia, there was strongly positive insulin (I: 79.8 μIU/mL) and C-peptide (CP: 14.5 ng/dl), thus establishing the diagnosis of endogenous hyperinsulinemic hypoglycemia. Simultaneously, there was appropriately concentrated urinary output, elevated urinary sodium levels, very low serum uric acid levels (1.05 mg/dl), and very high uric acid fractional excretion rates (40.2%), establishing the diagnosis compatible with SADH. Associated studies for adrenal glands, thyroid, kidneys, infections, and cranial images were negative. Decision for withdrawal of TAB/SMX was made and prompt disappearance of hypoglycemia and associated symptoms in 48h and slow improvement in serum levels were observed. Follow-up studies established persistent improvement one week following discharge from the hospital (serum Na levels: 132.7mmol/L; fasting blood sugar: 126 mg/dL). The adverse drug reaction was classified as probable by the Naranjo algorithm.

Conclusion:
To our knowledge, this is a unique presentation for biochemically documented TMP-SMX-induced potentiation of endogenous hyperinsulinemic hypoglycemia that co-exists with severe SIADH-mediated hyponatremia, and that resolves objectively after discontinuation of medications. It brings attention to a form of rare but potentially lethal form of endocrine toxicity that occurs in response to poly-pharmacotherapy in senior patients and emphasizes that extreme care be exercised with TMP-SMX co-use in diabetics that receive sulfonylureas and thiazides, respectively.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*