Urea Dosing for SIADH: Three Times Daily
For adults with SIADH, urea should be administered three times daily (every 8 hours) at a dose of 30-40 grams per dose, typically given orally or dissolved in normal saline. 1
Dosing Regimen
The neurosurgical guideline evidence specifically describes 40 grams of urea in 100-150 mL of normal saline given every 8 hours (three times daily) for 1-2 days in neurosurgical patients with hyponatremia 1. This translates to a total daily dose of 120 grams divided into three administrations.
Alternative dosing from research literature describes 30 grams given two to three times over 24 hours for rapid correction of symptomatic hyponatremia 2. When given as an infusion, 80 grams as a 30% solution over 6 hours has also been used 2.
Expected Response
With this three-times-daily regimen, you can expect:
- Serum sodium increase of approximately 5 mmol/L after 8 hours 2
- 9 mmol/L increase after 12 hours 2
- Correction to near-normal levels (>130 mmol/L) within 24-72 hours 1, 2
The mechanism works through osmotic diuresis and enhanced sodium retention induced by urea 2.
Critical Caveats
Do not confuse oral urea packets for SIADH with topical urea cream - the FDA drug label evidence provided 3 describes topical urea 20% cream for dermatologic use applied twice daily, which is completely unrelated to treating SIADH. This is a common source of confusion.
Adjunctive Therapy
Urea should be combined with:
- Fluid restriction to 500-1000 mL per 24 hours 1, 2
- Sodium supplementation (120-360 mmol/24 hours) 2
- Continuous normal saline infusion at 60-100 mL/hour when indicated 1
Safety Profile
The systematic review of 462 patients treated with urea found excellent safety, with no cases of osmotic demyelination syndrome reported 4. Adverse effects are minimal, primarily consisting of bad taste or dysgeusia 4. This makes urea safer than aggressive hypertonic saline correction in many scenarios.
Duration of Treatment
Treatment typically lasts 1-2 days for acute correction 1, though the median duration in the systematic review was 5 days 4. Once sodium reaches >131 mmol/L, transition to less aggressive maintenance therapy 1.