Would you add tolvaptan to manage difficult to treat SIADH in a patient who is already on high doses of sodium chloride tablets and urea but fails to reach adequate serum sodium levels?

First of all, I am NOT a fan of salt tablets for SIADH; it takes a bit over 7 one-gram salt tablets to equal the mmol supplied by a single 15-gram packet of urea.

And that many (large) pills can be nauseating, much more so than urea.

By far, I would prefer tolvaptan over urea, but tolvaptan is often not covered (a few hundred dollars a pill?), and urea is OTC and has to be paid out of pocket.

So add tolvaptan? If I should get tolvaptan, I would not add it to salt tablets; I would use it to replace salt tablets.

Yes. If a patient's hyponatremia fails to improve on high doses of NaCl tablets and urea, I would add tolvaptan to increase urinary electrolyte-free water clearance. In a patient with a very high urinary [Na + K]/plasma [Na] ratio, tolvaptan is often needed to increase urinary electrolyte-free water clearance to correct the hyponatremia.

I use tolvaptan a lot since it is now generic and no longer costs $$$$. Insurance often covers it with prior authorization if started in the hospital. I stop salt tablets, prescribe 30 tolvaptan 30 mg pills, and have the patient break them in half and take 1/2 pill every other day, and it’s usually sufficient. Patients also don’t have to gag on salt tablets.

For patients without insurance coverage, you can get it cheaper from Mark Cuban’s Cost Plus Pharmacy. Thirty 15 mg tablets cost $160, and thirty 30 mg tablets cost $260. You send in a prescription, the patient creates an online account and pays cash, and the medication is shipped to them within a couple of days.

We use much higher doses of tolvaptan in the outpatient setting for autosom...

If you're only increasing solute without adding a loop diuretic at the minimal dose required to suppress the tubular concentrating capacity and keep urine osmolality around 300, then fluid restriction alone, along with high solute intake, might not be enough.

Monitor the effect of the loop diuretic dose by checking a random urine osmolality within 2 hours of the dose, while avoiding dehydration as much as possible. Start, for example, with furosemide 10 mg by mouth, and once the desired effect is noted, increase the frequency.

I only give tolvaptan as needed, for example, when a procedure is scheduled, and there is a cutoff serum sodium level of 130 at times. When I do that, I avoid fluid restriction and cut down on the solutes given.