Hyponatraemia is among the metabolic disturbances encountered in oncology. Risk factors for hyponatraemia include chemotherapy, treatment-induced nausea and vomiting, hydration, pain, narcotic drugs and physical and emotional stress. A common cause of hyponatraemia in patients with cancer is the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), which may result from ectopic production of arginine vasopressin (AVP) by the tumour tissue.

The AVP-receptor antagonists, a new class of agents, correct hyponatraemia by directly blocking the binding of AVP with its receptors. In clinical trials, conivaptan, lixivaptan, tolvaptan and satavaptan have increased serum osmolality and normalised the serum [Na+] in hyponatraemia associated with SIADH, cirrhosis or congestive heart failure. These drugs may also have a potential in cancer-related hyponatraemia.

At this year's ENEA conference in Liege, Belgium, Otsuka sponsored a meet-the experts session to discuss the practical considerations for the use of novel therapies in the treatment of hyponatraemia secondary to SIADH. Among the discussion points were the appropriate use of vasopressin antagonists once an accurate differential diagnosis was confirmed, as well as selection, monitoring and length of treatment of patients with hyponatraemia.

This month, a randomised placebo-controlled Phase IV trial of tolvaptan in hyponatraemic patients with advanced cancer was registered and is currently enrolling subjects. The results of this study are expected in 2013.