The maximum volume allowed for a subcutaneous injection is 2 milliliters, according to the University of North Carolina. The shot is given into the fat layer located under the skin.
Rate of absorption of the drug is slower compared to intramuscular injection but more rapid than that of oral administration, according to the University of North Carolina. Injections are made in certain parts of the body such as upper arm, lower portion of the abdomen, anterior surface of the thigh and the upper back, according to Drugs.com. The University of North Carolina reports that heparin and insulin are examples of drugs routinely administered through subcutaneous injection.