1. Transfusion of blood to one who is fasting – such as if he bleeds heavily and is given a blood transfusion. This invalidates the fast because blood is formed from food and drink.
2. Receiving via a needle (as in the case of a drip) nourishing substances which take the place of food and drink, because this is the same as food and drink. Shaykh Ibn ‘Uthaymin, Majalis Shahr Ramadan, p/ 70.
With regard to injections which do not replace food and drink, rather they are administered for the purpose of medical treatment – such as penicillin or insulin – or are given to energize the body, or for the purpose of injections , these do not affect the fast, whether they are intravenous or intramuscular (injected into a vein or a muscle). (Fatawa Muhammad ibn Ibrahim, 4/189) But to be on the safe side, these injections may be given at night.
Kidney dialysis, in which blood is extracted, cleaned and then returned to the body with the addition of chemical substances such as sugars and salts etc. is regarded as invalidating the fast. (Fatawa al-Lajnah al-Daimah, 10/19)
Ref: islamqa.info