if the medicine is liquid you can mix it with some juice; my piggies definitely love diluited cranberry juice (it is very good also for bladder infections) which has a very strong flavour. It has a very little sugar therefore it is not bad for glycemia issues and inflammations (arthritis worsen with sugars in the diet). Only few drops drown out all the other flavours.
Of course at the beginning you should only offer pure cranberry juice (diluited!) as a treat; then some days later, if they appreciate it, you can hide some medicine in it. My piggies run towards the syringe and climb on me for reaching it...
If it works, I suggest a method for storing the juice (the bottle, once opened, needs to be drunk in few days). You can fill the holes of the "tray" for ice cubes (don't know the name, sorry...) and you will have 20-30 doses ready; once a day you defrost only one little cube. Remember to diluite 50% with water because the cranberry has a very strong flavour.