For desmopressin used to treat primary nocturnal enuresis, what is the recommended fluid restriction around dosing?

• A. Do not restrict fluids
• B. Restrict fluids 2 hours before and 2 hours after
• C. Restrict fluids only before taking
• D. Avoid drinking fluids for 1 hour before and 8 hours after taking desmopressin

Answer: (D)

Desmopressin lowers urine production by mimicking vasopressin, but it can cause the body to retain water. If a person drinks fluids around the time of taking the dose, this antidiuretic effect can lead to water overload and dilutional hyponatremia, which can be serious in children. To minimize this risk, fluids should be restricted around the dosing period: avoid drinking anything for about one hour before taking desmopressin and for about eight hours after. This window typically covers the entire sleep period, since the medicine is given at bedtime. The other approaches don’t sufficiently limit fluid intake during the vulnerable post-dose period, or they restrict for too short a time, so they don’t adequately protect against hyponatremia.