Injections should be done under the skin.
First of all you need to get help from a person who holds the cat still while the skin fold is lifted and the needle is inserted, pushing the liquid under the skin.
It's not painful and if you have a little dexterity it's the best method.
pills: Place the pill on the fingertip and insert it into the back of the cat's mouth, which will instinctively swallow it by swallowing. Then give the little friend a treat.
syrups and drops: They should be administered directly from the side of the mouth after having aspirated them with a syringe without a needle.
oral pastes or gels: The administration is identical to that of syrups or drops, the only difference is that these medicines are already contained in syringes without a needle.
If you are unable to administer syrups, drops, oral gels or pastes, you could try spreading the medicine on the kitten's paw so that she licks and swallows it. The disadvantage of this method of administering the drug is that the dose ingested cannot be precisely known.