Most medications prescribed for rats are oral liquids, as they are much easier to get the rat to take. Some medications are meant to taste good. Ask your veterinarian if the medicine you are given is flavored. If it is, rats will usually lick it right out of the syringe. It is always preferable to do it this way if you can, as it puts the least amount of stress on your rat, and he may even enjoy medication time! For medications that don't taste pleasant, you will have to draw it up in a syringe, stick the end of the syringe into the rat's mouth, and carefully press down on the plunger. It is best to stick the syringe in at an angle, towards the outside of the cheek. This will help avoid squirting it down the throat or windpipe, causing choking. If it is just a small bit of medication (0.1 - 0.3cc's), you can probably squirt it fairly quickly into the cheek of an adult-sized rat (babies you will have to go slower or do several small squirts) and they should swallow it.
Some medications require a larger dose (1cc or greater) and you will have to go more slowly. Rats can be quite difficult to medicate, and will learn when you bring that syringe up to them that they are about to have something unpleasant forced into their mouths. Restrain your rat as best you can (you may have to have someone help you), or wrap him in a towel like a burrito tightly enough that he cannot easily squirm out, though not tight enough that it hurts him. When giving larger doses of medication, go slowly and make sure the rat is swallowing, or he could easily choke if too much is put in his mouth too quickly. If you are having a lot of trouble giving your rat its medicine, talk to your veterinarian about other options.
You can also try mixing the medicine with some kind of liquidy food your rat loves, such as yogurt, chocolate syrup, baby food, or applesauce. If you only use a little bit of the medication, the rat will not taste it as easily, but you also have to make sure he eats the entire mix so he gets the correct dose. You will also have to make sure no other rats eat it, if your sick rat is in the same cage as healthy rats. If you use only a bit of the food, your rat may still taste or smell the medication and refuse to eat it. Experiment with different foods and amounts of each and hopefully you will find something that works for you.
Injections
Subcutaneous (under the skin, called Sub-Q for short), intramuscular (into the muscle; IM for short), and intravenous (into the vein; IV for short, rarely performed on rats) injections should only be given by a veterinarian or a veterinary technician. You should not attempt to give your rat an injection yourself unless specifically instructed by a veterinarian.
