There are 4 sites we can use for Intramuscular or IM injections, though 3 of them are the most common. The dorsogluteal, is rarely used due to its risk of damaging the sciatic nerve.
The other three sites are the vastus lateralis, found in the middle third of the lateral aspect of the thigh, the ventrogluteal, on the outside of the hip, and the deltoid muscle of the upper arm. Let’s look at these sites in detail.
To locate the vastus lateralis, visually divide the thigh into thirds vertically and draw a line directly down the front. You will inject in the lateral aspect of the middle third section.
To locate the ventrogluteal site, place the plam of your hand over the greater trochanter with your middle finger pointing toward the iliac crest and index finger toward the anterior superior iliac spine. Both of these sites can take up to 3mL of medication with a 1 to 1 ½ inch needle, depending on the size of your patient. The injection site for the deltoid muscle is 2-5cm (or about 3 fingers) below the lower edge of the acromion process.
For this site, use 1mL of medication and a 1 inch needle. This site has the most variance based on the size of your patient. A very large patient could handle 2mL and a 1 ½ inch needle.
However, a very small, frail patient, would require a ⅝ inch needle and no more than 1 mL. And remember, intramuscular injections should be administered at a 90 degree angle, with a gentle dart-like motion.