|Two available brands of NPH insulin, manufactured by Eli Lilly (Humulin N) and Novo Nordisk (Novolin N)|
Recently, several of my diabetic dog owners have asked if they can switch their NPH brand to Walmart's Relion/Novolin insulin to replace the Humulin N insulin that they are now using. It turns out that the Walmart ReliOn brand of NPH is much cheaper (only $25 per vial).
Though the two insulins both seem to be NPH insulin, I have some concerns about this change. Any concerns with the ReliOn brand or in switching from Humulin N to Novolin N insulin?
In theory, you'd think that Humulin N (Eli Lilly) and Novolin N (Novo Nordisk) would be bioequivalent (and therefore interchangeable), as they're just different brands of NPH insulin. However, that is not always the case.
Humulin N and Novolin N are made using different ingredients and manufacturing techniques, so they are not identical (1,2). Like you noted, Walmart sells NPH insulin as the Novolin/ReliOn brand for much less than most other pharmacies do, at only about $25 per vial (3).
A number of dogs have now been reported where they were stable and doing well on Humulin N. However, when switched to the same dose of Novolin N, their diabetic state was no longer regulated and the dogs developed signs of either hypo- or hyperglycemia, requiring significant dose adjustments (4).
Most dogs will respond well to the Novolin/ReliOn brand of insulin, which is indeed much less expensive than most other brands of NPH insulin. However, we cannot just assume that the two insulin preparations would be equivalent. I would not recommend switching from one insulin to the other without close monitoring (including blood glucose curves) so that the dose can be adjusted as needed.