I am not a vetsulin user so I am not too sure of the differences between it and lantus but from reading a bit in the past about others using it, I think I remember it being very necessary for the cat to eat about one hour before the shot, which is a big difference from lantus which is usually done just prior to the shot.
This is from the sticky in the vetsulin forum:
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http://www.felinediabetes.com/FDMB/threads/humulin-n-primer.303/
1. FOOD. Always make sure kitty eats about an hour before his/her shot. This will insure that kitty has food on her stomach to counteract the typical fast drop of the bg's caused by N (some cats do not drop fast on it, which is, again, why hometesting is so important!).
Feeding an hour ahead also leaves you relatively sure the cat is going to keep the food down. Warning: We are dealing with cats here, which means nothing is guaranteed. Bunny vomited at peak, while we were asleep, and that is how we had our first hypo in over 5 years of treating diabetes.
NOTE: Bunny free fed and seemed to know when he needed to eat, so we did not have to worry about his eating before hand. However, kitties getting timed feedings should be fed as stated.
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