Endocrine Abstracts

Introduction: Vasopression-2 receptor antagonists (VPAs) have been licensed for the treatment of hyponatraemia secondary to syndrome of inappropriate antidiuretic hormone secretion (SIADH). As usage extends to other causes of hyponatraemia, over-rapid correction and hypernatraemia remains as important side-effect. We present a patient with severe SIADH highlighting the need for guidance and vigilance when using these potent drugs.

Case: A 82-year-old lady was admitted for a total thyroidectomy for papillary carcinoma in December 2014 and commenced on tri-iodothyronine while awaiting radioiodine ablation. She developed severe hyponatraemia, drowsiness and confusion. On review, she had mild hyponatraemia prior to admission and developed severe hyponatraemia secondary to SIADH post-operatively. She was well hydrated, did not have excessive intravenous fluids and was not on any medication that could cause hyponatraemia or SIADH. Despite seven days treatment with fluid restriction and oral Demeclocycline 300 mg three times a day her serum sodium remained below 110 mmol/l. We then gave her a single dose of Tolvaptan 15 mg and checked her sodium levels every 6 h for 48 h and maintained fluid intake 1.5–2 l/day. Despite the rapid rise in her serum sodium levels (17 mmol/l in 24 h) her neurological symptoms improved and her mental test scores were normal.

Investigations: The patient’s biochemical test results are shown in the Table 1. A computerised tomography of her head, chest, abdomen, and pelvis did not demonstrate any pathology. Table 2 shows the response to a single 15 mg dose of Tolvaptan.

Conclusion: VPAs are potent drugs available for the treatment of hyponatraemia secondary to SIADH. Patients must be well hydrated (not on fluid restriction) and closely monitored to prevent over-rapid correction and hypernatraemia. We recommend 6–8 h serum sodium monitoring for the first 24–48 h after a single dose.