Just happened to "pop in" to see how things were going and read this thread. Metacam is good until the expiration date...and we have used it past the date. The script for Zithormax, as mentioned, is handled the same as a human drug.
The Tresaderm question lacks one work...refrigeration. This drug requires refrigeration at all times. If it has been out of the fridge for any extended amount of time, it is no longer of use and should be discarded. And a word of caution in using Tresaderm...while it is an excellent medication, it also contains a steroid and might not be the best choice of drugs in all situations. Using steroids of any kind brings on some possible problems in rabbits.