Whether injections invalidate fasting or not depends on the usage purpose of them. Injections are given in order to relieve pain, to treat a disease, to increase the resistance of the body and to give nourishment, etc. The injections that do not give nourishment or pleasure do not invalidate fasting because they are not regarded as eating and drinking. However, the injections that give nourishment or pleasure invalidate fasting. The same rule is valid regarding giving the patient blood or serum.