Anecdotal evidence from the Feline Diabetes Message Board shows that cats metabolize insulin noticeably faster than dogs or humans. Intervet acknowledges the faster metabolism of cats in their Australian Caninsulin presentation at the link below, as does this study of the absorption of R/Neutral, NPH/Isophane. and PZI/Protamine Zinc insulins in cats. From the Textbook of Veterinary Internal Medicine, Sixth Edition: *Levemir may be an exception; as we become familiar with more new types of insulin, we may have to modify this rule to depend on insulin types and molecules too.