I know. I'm speaking from a perspective on having some stock on hand... some are dangerous when expired, and some just loose potency. Thought it would be good info when storing some for a rainy day.
I looked up a couple antibiotics that are also used for fish and/or livestock.
This is from
http://www.drugs.com/doxycycline.html
"Store doxycycline at room temperature away from moisture and heat. Throw away any unused medicine after the expiration date on the label has passed.
Using expired doxycycline can cause damage to your kidneys."