Short answer

Pain a few days after an intramuscular (IM) injection could mean it wasn’t done properly. Question lacks the critical detail of injection site since there are four major sites of IM injection (see below from 1), and each has specific pros and cons, and different propensity for complications such as post-injection pain.

It’s the responsibility of the doctor who administered the injection to prescribe medications and/or other treatment to reduce post-injection pain.

Longer answer below for those interested in learning about IM injections in general, and sources of and approaches to minimize post-injection pain.

Brief Background On Intramuscular (IM) Injection Techniques

There are two main techniques used in IM injections to try to ensure injection is deposited in the muscle, and that injected material stays locked in it and doesn’t seep out into surrounding area along the needle track. They are the Z-track (see below from 2, 3) and air-lock techniques.

In the air-lock technique (3), a small amount of air is drawn up into the syringe along with the medication, the skin is stretched flat between two fingers and held taut, needle is plunged in at a right angle, injection includes medication followed by air, needle is withdrawn and taut skin is released. Rationale is the air locks in the medication in the muscle, hence air-lock, preventing it from seeping out into surrounding tissue along the needle track.

Possible Sources Of Pain After IM Injection

  • Aspiration is when the injector pushes the needle in but pulls back the syringe plunger before injecting the medication, rationale being to see if blood appears in the syringe meaning a blood vessel got punctured, i.e., need to try again. However, problems with aspiration are
    • No scientific support (4).
    • Can cause local tissue trauma and lingering pain (5, 6, 7, 8).
    • Is frequently done far too quickly to even be effective (4).
    • Isn’t recommended by National Immunization Technical Advisory Committees (9).
  • Inexperienced and/or unskilled injectors may end up injecting subcutaneously (SC) rather than IM, and cause undue local tissue trauma (10, 11).
  • Wrong choice of needle length can also increase chance of SC rather than IM injection. This is because ratio of subcutaneous to muscle varies by gender, age and weight, being higher in women (12, 13, 14, 15, 16, 17), older people and the obese (18, 19, 20, 21, 22). For example, a study infers a 12 to 25mm needle suffices for a thin person while a very obese person requires 76mm long needle for an IM injection (23).
  • Wiping needle with alcohol before injecting tracks it through the subcutaneous layer, which can be painful (24).

How To Minimize Pain After IM Injection

  • For something that’s a mainstay of routine medicine, shocking really that few sufficiently large, carefully controlled studies have compared different sites and techniques for their capacity to minimize pain after IM injection (25).
  • Consensus is slowly building that Ventrogluteal may cause less pain.
    • It isn’t close to large blood vessels, nerves, bone (1, 2, 10, 11, 25, 26, 27, 28, 29).
    • Being covered by relatively less subcutaneous tissue (15, 30) is another advantage since this reduces chances of accidental subcutaneous delivery (2, 27, 28).
    • However, there’s still insufficient conclusive data supporting it over Dorsogluteal (22).
  • OTOH, Dorsogluteal, though still much more commonly used compared to Ventrogluteal, has known risks such as
    • Sciatic nerve injury (26, 29).
    • Proximity to major blood vessels.
    • Increased thickness of subcutaneous tissue in this area compared to others (24), especially ventrogluteal (15, 30).
  • Injection techniques: A couple of small controlled studies (n=90 females aged between 18 and 60 years of age, 31; n=60; 32) suggest the air-lock technique can reduce tissue trauma and pain from IM injections.
  • Relaxed muscles can reduce injection site discomfort and pain (24). This means appropriately positioning the body, particularly the limbs, before IM injection. Studies (33, 34) suggest
    • Placing the hand on the hip relaxes the deltoid muscle.
    • Internal rotation of the femur relaxes the gluteal muscles.
  • No pain at initial point of needle contact on skin (24, 35). If there is pain, better to move needle 2 to 3mm at a time until reaching a painless point on the skin. Rationale is differential skin innervation, i.e., hitting upon a skin site with fewer or no pain receptors.
  • A randomized study (n=100) showed that changing needle after drawing up the medication and before injecting can minimize pain by ensuring needle tip used for injection remains sharp and free of medicine residue (36).
  • Briefly applying manual pressure to injection site before IM injection can minimize post-injection pain (6; n=48, 45 experimental and control, respectively, 37; n=74, one injection per arm, manual pressure randomly assigned, 38; n=63, 60 experimental and control, respectively, 39).


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