An injection involves using a needle and a syringe to place a given amount of medication in a patient’s body by a route other than by mouth. There are some medications that are only affective if given by injection and there are several ways of providing the necessary injection. Medications that are safely given via one injection route are not necessarily safe when using another route.
A subcutaneous injection is effective for several drugs and situations. In this type of injection, medication is delivered, often in small amounts, into the subcutis layer of skin, which is just under the dermis and epidermis. Often, the skin rises up at the site for a brief period, forming a “wheal”.
Subcutaneous injections are simple to give and patients can often be taught to give the injection themselves. Injection sites commonly used for this type of injection are the upper outer arm, the abdomen, the upper area of the buttocks and the front of the thigh. Often patients will alternate sites to lesson the risk of lipodystrophy or small areas of bumps or dents that form on the surface of the skin.
Medications commonly given via subcutaneous injection are insulin, terbutaline (for preterm labor), gosrelin (an anti-estrogen) and heparin (a blood thinner). Subcutaneous injections are simple to give but have variable rates of absorption into the body and are therefore not good for acute emergencies.
Intramuscular injections are more difficult to give and involve placing the tip of the needle inside a large muscle before injecting the medication. Children receive vaccinations on their outer arm (deltoid muscle) or anterior thigh (quadriceps muscles) via intramuscular injection. Some antibiotics are given by intramuscular injection as well. Medicines for pain relief, such as Demerol, are given intramuscularly.
While the upper aspect of the buttocks is the preferred site for this type of injection, particularly if the volume of fluid is greater than 2 milliliters, the deltoid muscle of the upper arm is not uncommonly used. As with subcutaneous injections, the rate of absorption is not immediate and varies with the type of medication.
Intravenous injections involve the ability to first cannulate (enter) a vein in order to provide an immediately absorbed medication. Many times, a single injection into the vein isn’t practical, so an IV catheter is placed into the vein and medications are then introduced through the catheter. Medications by this route can be given continuously as an “IV drip” or can be injected into the IV line via a port and then flushed into the vein through the line. Some IV injection systems are called “needle-less” because, once the IV is placed, medication is introduced into the line via specially-adapted syringes and ports that do not involve the risk of sustaining a needle poke.