It is used to control Diabetes Insipidus (nothing to do with sugar diabetes) It is a hormone that controls water balance. Cats drink and pee a lot without it. Often the symptoms are confused with kidney disease.
It is rare in dogs and even rarer in cats, but our Laz had it. If anyone has use for it, please let me know. It isn't the type of thing someone might keep for 'just in case' - I offered it to Dogs Trust, but they don't take donated meds - even sealed ones.
If anyone has an animal on it,they are welcome to it. It would be a shame to throw it away. The bottles only contain 2.5ml each,but vets charge over £40 a bottle for it. (I bought 6 at a time online for about £15 a bottle)
It needs to be kept chilled, but a day or so in the post shouldn't hurt in the winter.