Does your guinea pig have dry scaley skin? Does it scratch itself constantly and make noises like it just can't get comfortable? Does it sometimes fall on its side and seem to be twitching like a seizure? Chances are your guinea pig is suffering from skin mites or some other skin parasites (ectoparasites).
Guinea pigs often develop bladder stones composed of calcium carbonate. This can be the result of improper diet and cause a bladder infection. The bladder stones of guinea pigs cannot be dissolved with special medications or diets.
If your guinea pig is not eating well, it needs to be started on a diet such as Oxbow's Critical Care for Herbivores right away. It is much easier to help a sick guinea pig that has been assist fed until you are able to have it seen by a doctor than it is to help one that has been hungry and thirsty for several hours. Make sure that your guinea pig is also getting one or two tablespoons of water by mouth several times a day.
Pets may be sent home with liquid medications. An oral liquid medication must be given by mouth to be effective. An injectable liquid medication must be given by injection beneath the skin to be useful. Some injectable medications require that the medication is inserted into the muscle to be most effective. It is important that you understand how to read the syringes that are sent home so your pet gets the proper amount of medication at each dose.