Intramuscular Injection Technique for Nurses: Sites, Volumes, Needle Length and the Z-Track Method

Intramuscular (IM) injections are one of the most common procedures nurses perform, from vaccines and antibiotics to depot antipsychotics, vitamin B12 and contraceptive injections. Because they are so routine, it is easy to slip into habits learned years ago. But poor technique can cause pain, abscesses, nerve damage and medicine that doesn’t work as intended. This guide sets out current good practice.

Why the intramuscular route?

Muscle has a good blood supply, so IM medicines are absorbed faster than subcutaneous ones but more slowly than intravenous medicines. The route is used when a medicine:

• Is irritating to subcutaneous tissue
• Needs a depot effect (slow release over weeks)
• Can’t be given orally, or needs to work faster than an oral dose
• Is a vaccine designed for muscle

Choosing the right site

Ventrogluteal (the preferred site for most adult injections)

The ventrogluteal site, on the side of the hip, is recommended by many nursing texts and guidelines for larger or irritant injections in adults and children over 7 months. It has thick muscle (gluteus medius and minimus), a thin layer of fat in most people, and no major nerves or blood vessels nearby.

Finding it: With the patient lying on their side (or on their back), place the heel of your hand on the greater trochanter of the femur. Use your right hand on the patient’s left hip and vice versa. Point your index finger at the anterior superior iliac spine and spread your middle finger back along the iliac crest to form a “V”. Inject in the centre of the V.

Deltoid

The deltoid in the upper arm is easy to reach and is the usual site for most adult vaccines. It is a small muscle, so it is suitable only for small volumes, usually up to 1 mL in adults (some sources allow up to 2 mL in a well-developed muscle).

Finding it: Expose the whole upper arm. Find the acromion process at the top of the shoulder. The injection site is in the centre of the muscle, about 2.5 to 5 cm (two to three finger-breadths) below the acromion. Injecting too high can damage the shoulder joint (sometimes called shoulder injury related to vaccine administration); too low or too far back risks the radial nerve.

Vastus lateralis

On the outer front of the thigh, this is the preferred site for infants under 1 year and is also used in adults, for example for self-injection.

Finding it: Divide the thigh between the greater trochanter and the knee into thirds. Inject into the middle third, on the outer (anterolateral) aspect.

Dorsogluteal: why it is discouraged

The traditional “upper outer quadrant of the buttock” site is still used in many hospitals worldwide, but it carries a risk of injury to the sciatic nerve and the superior gluteal artery. Fat over the buttock is often thick, so injections can end up in fat rather than muscle. Where possible, choose the ventrogluteal site instead. If local policy still uses the dorsogluteal site, be very careful with landmarks and never inject into the lower or inner areas.

Maximum volumes (general guide)

• Ventrogluteal: up to 2.5 to 3 mL in adults
• Vastus lateralis: up to 2.5 to 3 mL in adults; 0.5 to 1 mL in infants
• Deltoid: usually up to 1 mL

Always follow the manufacturer’s instructions and local policy. Some depot medicines have specific volumes and sites.

Choosing the needle

• Gauge: 21G to 23G for most adult IM injections; 25G is commonly used for vaccines. Thicker (lower number) needles are needed for oily or viscous medicines.
• Length: the needle must be long enough to reach muscle. Many adults need 25 mm (1 inch); larger adults, or injections into the ventrogluteal site in people with more body fat, may need 38 mm (1.5 inches). Infants usually need 16 to 25 mm depending on site and size.

Using a needle that is too short is a common reason for injections ending up in subcutaneous fat, which can cause nodules and poor absorption.

Step-by-step procedure

1. Check the prescription and apply the rights of medication administration: right patient, medicine, dose, route, time, and check for allergies.
2. Explain the procedure and get consent. Offer privacy and a chaperone where appropriate.
3. Perform hand hygiene and prepare the medicine using aseptic non-touch technique. Change the needle after drawing up if local policy advises it.
4. Position the patient so the muscle is relaxed, for example lying on their side with the upper knee bent for ventrogluteal injection.
5. Locate the site using anatomical landmarks. Check the skin for bruises, scars, inflammation or previous injection lumps, and rotate sites.
6. Skin cleaning: follow local policy. Many guidelines say skin that is visibly clean doesn’t need an alcohol swab; if you use one, let the skin dry completely to reduce stinging.
7. Insert the needle at 90 degrees in a quick, smooth motion, leaving a small part of the shaft visible.
8. Aspiration: routine aspiration is no longer recommended for vaccines (WHO and many national immunisation guidelines), and many guidelines no longer require it for other IM injections at the recommended sites. Some local policies still require it for the dorsogluteal site or certain medicines. Follow your organisation’s policy.
9. Inject slowly, about 1 mL every 10 seconds, to reduce pain and allow the muscle to accommodate the fluid.
10. Wait about 10 seconds, then withdraw the needle smoothly at the same angle.
11. Apply gentle pressure with gauze. Don’t massage the site unless the medicine instructions say so.
12. Dispose of the sharp immediately into a sharps container. Never recap.
13. Document the medicine, dose, site, time and batch number (for vaccines), and observe the patient for reactions.

The Z-track technique

The Z-track method seals medicine in the muscle and stops it leaking back into subcutaneous tissue. It is particularly useful for irritant or staining medicines (such as iron injections) and many guidelines now recommend it for all IM injections in adults.

1. With your non-dominant hand, pull the skin and subcutaneous tissue about 2.5 to 3 cm to one side and hold it.
2. Insert the needle at 90 degrees and inject slowly while keeping the skin displaced.
3. Wait 10 seconds, withdraw the needle, then release the skin.

The tissue layers slide back into place, creating a zig-zag track that seals the medicine in.

Reducing pain

• Let alcohol-based skin cleaning dry fully.
• Use a new, sharp needle and the right length.
• Help the patient relax the muscle.
• Inject slowly.
• For children, use distraction, comfort holding and age-appropriate positioning. Breastfeeding during infant vaccination can reduce distress.

Complications to watch for

• Pain, bruising and bleeding (especially in patients on anticoagulants or with low platelets)
• Sterile abscess or infection
• Nerve injury: severe shooting pain or numbness during injection means stop immediately and report
• Allergic reactions, including anaphylaxis. Know where your anaphylaxis kit is and how to use adrenaline.
• Fainting (vasovagal reactions), particularly in young people having vaccines. Seat or lie patients down.

Safety reminders

• Never inject into an area that is inflamed, oedematous, scarred or paralysed.
• Be cautious in patients with low platelets or bleeding disorders; an alternative route may be safer.
• Single-use needles and syringes only. Reusing them spreads HIV, hepatitis B and hepatitis C.
• Report needlestick injuries immediately.

A perfect IM injection is quick, nearly painless and forgettable for the patient. Getting the site, needle and technique right every time is one of the simplest ways nurses can improve comfort and safety.

References

• WHO: Best practices for injections and related procedures toolkit
• US CDC: Vaccine administration best practices
• UKHSA Green Book Chapter 4: Immunisation procedures