Insulin lispro has been known to "wilt" easily when not constantly refrigerated. Those who have had bad vials report finding hazy or small particles on inspection. Humalog degrades rapidly--it can be working well one day but not the next. Dr. Nelson of University of California-Davis said in his lecture at the Ohio State Endocrinology Symposium in 2006 that if the short-acting analog insulins have any role in feline and canine diabetes, it is not yet determined. These are human activity profiles.