It could be allergies, or allergic reaction to the meds, or something new on them, in them, or in their world. What kind of meds, and who is the maker? You should call the maker of the medications.
You also should figure out what your cat might have gotten into. Or, was he in a fight. Does he have green snot like puss coming out of eyes?? Could be a scratch on eye, or lid, or even a bacteria infection- but there could be worst things that need to be remedied.
Swelling might not be a good thing. Some cats can also get those problems, if they are in wet areas too long, or even if the box is dirty, ammonia smell. Or even a bad cat litter you're using, or even the fleas stuff you have on them. If you just recently washed them, or put flea poison on them, or in their world, or a collar- then you should get rid of it, and get it off of them quickly.
Allergies can be very serious. Take the unknown things out of their environment. Put them in a place where they can relax.... Did you just recently feed them something new, or different. Some products are very anti-cat... What state are you in? Maybe you have an animal poison center call number. Check your phone book.