Do you have any specific recommendations to prevent large fluctuations in sodium levels during a colonoscopy prep in patients with central diabetes insipidus on DDAVP?

Interesting, I have just received a message from a patient in this very same situation. I am not aware of any specific literature on this. In absence of such data, I usually recommend remaining on the same desmopressin dose and obeying to thirst, as I worry about hyponatremia that may be caused by an increase in desmopressin dose.

I agree there are no standardized recommendations. Some literature suggests that up to 7% of normal patients can develop hyponatremia associated with colonoscopy, so extra desmopressin could indeed be problematic. In many of our patients with diabetes insipidus and completely intact thirst, we advise them to occasionally (once a week or so) skip a dose of ddavp and allow some "breakthrough" symptoms which is protective against hyponatremia. One might remind this patient to do this 1-2 days after...

I agree with Dr. @Dr. First Last. Colonoscopy prep does not require any change in liquid intake so I don't expect that any change in DDAVP dose would be required.