Urea is a hyponatremia
treatment long forgotten in the United States. Chronic SIADH is
usually managed either by vaptans or a combination
of fluid restriction, salt and furosemide.
However, vaptans are very expensive and few
patients can afford it. In a recent Belgian article ,
the use of urea as a comparable, cheaper
alternative is being advocated
What do we know about urea? It
is a very
cheap powder (< $0.50/30 gram) that works
by increasing free water excretion through osmotic diuresis. Shown below is the solute excretion as a
determinant of free water excretion
clearance = solute excretion/Uosm x
(1 - Uosm/Posm)
Physiologically it makes sense, but does it really work? In this
article, 13 patients with SIADH were tried on vaptans
(satavaptan or tolvaptan) for 12 months. Then vaptans were discontinued for 8 days and urea was started after ensuring that their Na level came down. The result? It worked as well as
vaptans! Side effects included hypernatremia and gastric irritation but no
osmotic myelinolysis has been reported with urea. It does not cause volume
overload (unlike salt), hypokalemia (unlike diuretics), or uremia. You will not
become uremic even if your BUN is 100 after you take urea (but you will be
urinating a lot!).
So why are we not using it? Are you a fan of bitter drinks? We know
Belgians are (great beer there!). In Belgium, only about 15% of patients
discontinue to take urea due to its taste. In Canada, Dr.
Bichet tried it himself (mixed with orange
juice) and wrote “it does not smell of anything but the bitterness is strong”. On this side of the border, Dr. Berl wrote that it is “rarely compatible with North American palate”.
That being said, it may be a time to use urea again as a comparable,
cheaper alternative for hyponatremia treatment. Across the Pacific (in Japan) there is
a proverb “good medicine tastes bitter”.