**Question:** Which of the following nasal spray is very effective in control of enuresis –

A. Mepenzolate
B. Doxylamine
C. Desmopressin
D. Phenylephrine

**Core Concept:** Desmopressin is a synthetic analog of vasopressin, a hormone secreted by the posterior pituitary gland. It acts as a potent antidiuretic hormone (ADH) and is used for the treatment of conditions involving excessive urine production, such as nocturnal enuresis (bedwetting) in children and nocturia (incontinence of urine during sleep) in adults.

**Why the Correct Answer is Right:** Desmopressin is an effective treatment for enuresis due to its ability to reduce urine production by inhibiting the action of vasopressin on the collecting ducts of the nephrons in the kidneys. This leads to a decrease in urine volume and concentration, which helps control nocturnal enuresis.

**Why Each Wrong Option is Incorrect:**

A. Mepenzolate: Mepenzolate is a muscarinic receptor antagonist used for the treatment of gastrointestinal disorders like gastroparesis and cholinergic urticaria. It does not have any direct effect on urine production or control of enuresis.

B. Doxylamine: Doxylamine is an antihistamine with sedative properties, used for treating insomnia and allergies. It does not specifically target urine production or control nocturnal enuresis.

C. Phenylephrine: Phenylephrine is a sympathomimetic alpha-agonist used for vasoconstriction in various medical conditions. It does not modulate urine production or treat nocturnal enuresis.

D. Phenylephrine: Similar to option C, Phenylephrine is a sympathomimetic alpha-agonist used for vasoconstriction in various medical conditions. It does not modulate urine production or treat nocturnal enuresis.

**Clinical Pearl:** Desmopressin is the correct answer because it is a selective agonist of the V2 receptors in the kidney, which leads to the inhibition of the action of antidiuretic hormone (ADH) on the collecting ducts, reducing urine production and controlling nocturnal enuresis.