Endocrine Abstracts

Introduction: Tolvaptan is an oral vasopressin V₂ receptor antagonist which offers a targeted approach in regulating body water and serum [Na⁺] and is a novel treatment for hyponatraemia secondary to SIADH. Here we report our first case experience with tolvaptan comparing its efficacy with conventional treatments in the same patient.

Case report: A 52-year-old lady was admitted with confusion, nausea and vomiting. She gave a 3-month history of increasing breathlessness, anorexia and weight loss. Her comorbidities included hypothyroidism, hypertension and hyperlipidaemia. She had 45 pack years of smoking history. On clinical examination, left lateral rectus palsy resulting in diplopia was noted. From subsequent investigations she was diagnosed with hyponatraemia secondary to SIADH (serum [Na⁺] 115 mmol/l) due to metastatic small cell lung cancer T2N2M1b (pituitary fossa). Palliative chemotherapy was commenced. Symptomatic hyponatraemia was initially treated with fluid restriction (0.8–1 l/24 h). Serum [Na⁺] improved to 135 mmol/l in 2 weeks with a gradual decline thereafter reaching 110 mmol/l at 2 months. During this time she had two recurrent admissions with symptomatic hyponatraemia which delayed her chemotherapy. She then received demeclocycline 300 mg TDS during her inpatient stay and serum [Na⁺] increased from 110 to 115 mmol/l over 5 days. As any improvement in serum [Na⁺] with conventional treatments had been slow and marginal, tolvaptan 15 mg PO OD was initiated. Within 36 h, serum [Na⁺] showed significant improvement (from 115 to 127 mmol/l). Her clinical condition improved and she was discharged on tolvaptan. Serum [Na⁺] remained normal and she experienced no adverse effects while taking tolvaptan for 35 days. Unfortunately, she then died from the combination of progressive disease and chemotherapy complications.

Conclusion: In a patient with hyponatraemia secondary to SIADH, tolvaptan raised serum [Na⁺] levels more promptly than fluid restriction or demeclocycline, improving clinical condition and enabling discharge from hospital, and was well tolerated.