Secondary resistance to tolvaptan in two patients with SIAD due to small cell lung cancer
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Syndrome of inappropriate antidiuresis (SIAD) is characterized by euvolaemic hyponatraemia due to the antidiuretic effects of inappropriate elevation of plasma vasopressin (pAVP, also referred to as antidiuretic hormone (ADH)). Randomized controlled trials report a good response to tolvaptan-induced vasopressin receptor blockade, with reversal of hyponatremia in SIAD , including those with lung cancer . Prolonged treatment is effective for up to four years . We report two patients with small cell lung cancer (SCLC) who showed an initial good response to tolvaptan, but who subsequently displayed resistance to the aquaretic effects of the drug.
We thank Dr. Chris Boot (Newcastle upon Tyne) for the measurement of plasma copeptin.
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Conflict of interest
Professor Chris Thompson has received honoraria for lectures from Otsuka.
Dr. Aoife Garrahy, Dr. Anne Marie Hannon, Dr. Zia-Ul-Hussnain, and Professor David Williams have no potential conflicts of interest.