Endocrine Abstracts

Introduction: Contrary to US guidelines, recent European guidelines do not recommend tolvaptan for the treatment of SIADH.

Methods: Retrospective data collection of all inpatients treated with tolvaptan for SIADH in two UK hospitals between November 2010 and February 2014. All values were calculated as mean±S.D.

Results: This case series included 61 patients (33 females, 28 males) aged 74.4±15.3 years with serum sodium (sNa) 119.9±5.5 mmol/l. The aetiology of SIADH was malignancy (24.6%), unknown (24.6%), pulmonary (14.7%), neurosurgical (11.5%), drug-induced (9.8%), post-operative (9.8%) and various (5%). Initiation tolvaptan dose was 15 mg in 55/61 and 7.5 mg in 6/61 cases. 24 h after administration of tolvaptan, sNa increased by 9±3.9 mmol/l; specifically, 2–8 mmol/l in 45.9%, 9–10 mmol/l in 16.4%, 11–12 mmol/l in 19.7% and >12 mmol/l in 18% of patients. Overcorrection, defined as sNa increase of >12 mmol/l in 24 h or >18 mmol/l in 48 h, was observed in 22.3%, while increase of >10 mmol/l in 24 h occurred in 39.3% of patients. No patients developed osmotic demyelination syndrome. None of 12 patients with baseline sNa ≧125 mmol/l exhibited increase >10 mmol/l in 24 h. The duration of tolvaptan use was 4.2±4 days. At the end of tolvaptan therapy, sNa increased by 13.5±5.9 mmol/l with only 2/61 (3.3%) ‘non-responders’, having sNa increase ≤5 mmol/l or sNa ≤130 mmol/l.

Five days after withdrawal of tolvaptan, mean change of sNa was −3.8±6.6 mmol/l with sNa reduction by ≧5 mmol/l in 21/50 (42%) patients.

Conclusions: Tolvaptan is effective, but can often lead to overcorrection of hyponatraemia. Physicians should monitor closely sodium levels and take appropriate measures to prevent or reverse overcorrection, especially in patients with baseline sNa ≤125 mmol/l.