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How to care for a guinea pig with a long term injury
Get a vet-advised painkiller for your pet.
Many vets who look after small animals will be able to get dosages in guinea pig sizes. Follow your vet's advice as to dosage and method for giving to your pet.
If your vet advises against such usage, then skip this step. Get small, thin syringes that you can fill with water and keep a bowl handy.