A recent discussion titled "Need an Answer ASAP" asked whether it would be OK to use an insulin pen that had been kept in a car for a week in the Arizona summer heat. The answers received were across the board. My questions to an expert are 1.) Would using insulin subjected to such conditions be harmful? 2.) What is the expectation of having such insulin be effective? 3.) Does it depend on the type of insulin used?
All insulins are made up of proteins and will decompose when exposed to extreme heat, regardless of the type of insulin. Temperatures inside a closed car in Arizona get well above 120 degrees and would likely cause significant deterioration of the protein molecules. The level of deterioration under these conditions is unknown, but the more deterioration there is, the less effective the insulin will be. Would it cause harm? It depends on the type of diabetes a person has. In type 1 diabetes, taking ineffective insulin can cause significant harm in the form of diabetic ketoacidosis. If a person has type 2 diabetes, the only likely harm would be high glucose levels. At those temperatures, I would also worry about the buildup of bacteria within the insulin pen or vial. Preservatives do protect against some of this, but at those temperatures for that length of time, I would expect some abnormal growth of organisms within the vial or pen. Injecting a liquid that might be contaminated with organisms can increase the chance of infections at the site of injection.