There was a thread not too long ago about the expiration date of (if I recall) LA200/300. I'll be darned if I can find it now, but I believe the clock starts ticking once the seal is cracked.
Good point Jeanne.Yes. My vet told me if stored properly and HANDLED properly, it is effective for a long time.
But. Handling properly also means you NEVER insert a used needle into the bottle. So easy to break that rule. You get a new needle and syringe, draw 20cc, inject it and draw another 20cc. Contaminated the whole bottle.
I feel the taking care of the product is more important than the expiration date. As stated if not contaminated and not allowed to get too hot, freeze, not be in sunlight will extend the time it could be used.As was explanined to me at a cattle conference. If the drug is taken care of as mentioned, the expiry date is when it theoretically starts to lose some of its potency. A year after expiration it may only work at 75% as good as a new product.