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Idiopathic nocturnal polyuria — MSRA MCQ

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HardLUTSIdiopathic nocturnal polyuriaMSRA

A 68-year-old man has persistent nocturia despite fluid advice and successful treatment of his voiding LUTS with tamsulosin. A 3-day frequency-volume chart confirms nocturnal polyuria, with three nocturnal voids and nocturnal urine volume comprising 48% of his 24-hour output. He has no peripheral oedema, heart failure, sleep apnoea, diabetes mellitus, renal disease or symptoms suggesting urinary retention. His creatinine clearance is 64 mL/min and serum sodium is 137 mmol/L. He has not benefited from other conservative measures. He is considering treatment with Noqdirna (desmopressin oral lyophilisate). Which is the most appropriate prescribing and monitoring plan?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Start Noqdirna 50 micrograms sublingually 1 hour before bedtime, restrict fluid intake from 1 hour before until 8 hours after dosing, and measure serum sodium before treatment, at 4–8 days and at 1 month.

This man has documented nocturnal polyuria after relevant medical causes have been excluded and conservative measures have failed, so desmopressin can be considered. His creatinine clearance is above 50 mL/min, sodium is normal, and there is no heart failure or other fluid-overload state requiring diuretics; these features exclude key contraindications. For Noqdirna, the licensed male dose is 50 micrograms sublingually 1 hour before bedtime. Fluid intake must be kept to a minimum from 1 hour before until 8 hours after administration to reduce water retention and hyponatraemia. Patients aged 65 years or over require sodium measurement before treatment, at 4–8 days and again at 1 month. Therefore C is the complete licensed plan. A uses the lower female dose. B omits the essential early and subsequent sodium monitoring required in an older patient. D includes the one-month test but misses the early 4–8-day sodium check, when hyponatraemia commonly develops. E incorrectly treats age over 65 as an absolute contraindication: age increases hyponatraemia risk and requires enhanced monitoring, rather than precluding treatment.

Reference: Noqdirna 25 microgram oral lyophilisate — Summary of Product Characteristics (Last updated 15 June 2026) — https://www.medicines.org.uk/emc/product/4368/smpc Noqdirna 25 microgram oral lyophilisate — Summary of Product Characteristics (Last updated 15 June 2026) — https://www.medicines.org.uk/emc/product/4368/smpc Noqdirna 25 microgram oral lyophilisate — Summary of Product Characteristics (Last updated 15 June 2026) — https://www.medicines.org.uk/emc/product/4368/smpc