September 20, 2024

Welcome back to UH EMS-I’s Pharmacy Phriday. In this installment we continue our series reviewing the various medication routes used by our providers, this time focusing on the Intramuscular (IM) injection. 

IM injections are a useful means to administer various medicines when rapid effects are not required. They can be used in various applications including the prehospital setting. Within the UH EMS Protocol there are 15 different medications in various circumstances that can be administered using this route. You may recall that the recently revised Ohio Scope of Practice has also expanded use of the route for the EMT basic by including Epinephrine IM injections via syringe in cases of anaphylaxis. 

An IM injection uses a needle long enough to enter through the dermis, subcutaneous tissue and into the muscle. Large muscles have good vascularity, and therefore the injected drug quickly reaches the systemic circulation. Using this route the medication bypasses the “first pass metabolism” discussed in the last installment. The average onset of medications administered IM is about 10-15 minutes. Absorption can be affected by blood flow to the site, the bulk of the muscle chosen, and the accuracy in determining the landmarks of the chosen injection site.

The most common muscles used include the deltoid, thigh (vastus lateralis), and gluteus. Depending on the chosen site, various volume limits exist. The larger muscles obviously allow a larger volume of fluid and the total volume needed to be administered can sometimes determine the site chosen.

Within the UH EMS Protocol the volume limits allowed in the deltoid muscle is 1 ml, and within the thigh and gluteus the volume limit is 2.5 ml. For pediatric patients the protocol recommends the use of the thigh muscle and limits volumes to 1 ml. Use of a 1-3 ml syringe is recommended. When giving volumes less than 1 ml, use of the 1 ml syringe with smaller increments is suggested to allow accurate dosing.

Needle size is also an important consideration in administering an IM injection. Proper needle length is a key factor in ensuring the IM injection reaches the muscle tissue. Patients with increased body mass index may necessitate a larger needle, but the provider should use the smallest gauge needle capable of reaching the muscle. This is typically taught as requiring a 21-to-25-gauge needle 1 to 2 inches in length. Most UH drug boxes supply a 22-gauge needle that would generally be the needle of choice. For the pediatric patient, UH protocol recommends the length of the needle no longer than 1 inch.

Proper identification of the site is important to assure effectiveness of the administration and to avoid damage to blood vessels and nerves. The deltoid muscle is in the upper arm located 1 ½ to 2 inches below acromion process. (Note: This site should not be used if the person is very thin or the muscle is very small.) Proper identification of the landmark is often instructed using the triangle method (see illustration #1 below).

The landmark for the thigh, or vastus lateralis, is the lateral middle aspect of the thigh. The buttocks, or Gluteus, is located by imagining 4 quadrants on the muscle. The injection should be placed in the upper outer quadrant to avoid the sciatic nerve. (See illustration #2) 

Key points to remember when administering an IM injection include:

Always consider the “Five Rights” of medication administration

Educate the patient and obtain consent (if they are alert, cooperative, etc.)



• If drawing up medication from an ampule, remember to use a filtered needle and replace the needle before administration

• When administering the medication stretch the skin taut over the site

• Insert the needle at a 90 degree angle in one swift motion

• Information on aspiration (pulling back on the plunger for 5-10 seconds, looking for blood) is mixed. The step is used to assure the needle has not entered a blood vessel. If blood is present, the provider should not inject the medication but remove the needle and begin again choosing another site. Note that aspiration is still listed as a step in the UH protocol.

• Inject the medication slowly (reduces pain and improves retention of medication without leaking out the needle track)

• Dispose of the needle and syringe properly

• Apply pressure to the injection site and cover with a band aid

• Monitor the patient and document the administration properly

• Be cautious if the patient is uncooperative and moving about. This obviously increases the risk of a needle stick injury to the provider

• Never use a site where active infection, cellulitis, or dermatitis is present

• IM injections are not recommended in patients suffering hypovolemic shock due to possible decreased blood flow to the site

Till the next installment of Pharmacy Phriday, stay safe!



The UH EMS-I Team

University Hospitals