The long-lasting Humulin U and Humulin L and their Novo Nordisk equivalents have all disappeared by now, and some feline (and perhaps canine) caregivers are desperately looking for substitutes. Some brands of PZI are also being discontinued, but not all. About your current saved-up supply of Humulin U or L: Health Canada has investigated some Lilly insulins and found them to be stable up to a year beyond their expiry date. See Substitutes for Iletin II NPH.