31 years ago I was placed on lithium for 5 years.  Without proper supervision and instruction in usage I had permanent kidney damage and have suffered from diabetes insipidus - nephrogenic type since then.  (For the readers who are unfamiliar with this type of diabetes, it has nothing to do with the pancreas or sugar.  It simply means that I can't stop urinating because my kidneys, in this case, can't regulate the fluid in my body.)   I've had to take a daily diuretic pill and lots of potassium.  After being put on topomax my need for a diuretic disappeared.  Is there something chemically different about topomax that affects the kidney in that it acts upon the loop of the kidney in much the same manner as the diuretic did which replaces the need for the diuretic?  I still require the same dose of potassium, I just no longer need the diuretic.  It's so strange after 26 years!  I've been unable to get an answer for this question.

Thank you,
Donna
 

Dear Donna -- 
Well, that's interesting.  I'm not positive about this, but here's my hunch:  topiramate (Topomax) is known to act like a "carbonic anhydrase inhibitor"^Dodgson (this is related to why the risk of kidney stones goes up with this medication; keep drinking! (water, that is)).  

Carbonic anhydrase inhibitors can act like diuretics in the kidney (if you want to show your doctor a reference on this, here's one I found trying to remind myself whether I was remembering this correctly).  

Putting two and two together, I'd say that might add up to four!

Dr. Phelps
 

Published September, 2003