Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Intramuscular injection is the injection of a substance directly into a muscle. In medicine, it is one of several alternative methods for the administration of medications (see Route of administration). It is used for particular forms of medication that are administered in small amounts. Depending on the chemical properties of the drug, the medication may either be absorbed fairly quickly or more gradually. Intramuscular injections are often given in the deltoid, vastus lateralis, ventrogluteal and dorsogluteal muscles. When the gluteal muscles are used, injections should be made on the upper, outer quadrant of the buttock to avoid damaging the sciatic nerve. Injection fibrosis is a complication that may occur if the injections are delivered with great frequency or with improper technique.
Thrombocytopenia (low platelet counts) and coagulopathy (bleeding tendency) are contraindications for intramuscular injections, as they may lead to hematomas.
Examples of medications that are sometimes administered intramuscularly are:
- Interferon beta-1a
- sex hormones, such as testosterone, estradiol valerate, and Depo Provera
- quinine in its gluconate form
In addition, some vaccines are administered intramuscularly:
- hepatitis A vaccine
Also certain substances (i.e. ketamine) are injected intramuscularly for recreational purposes.
If a subcutaneous injection is inadvertently administered as an intramusclular injection, a hematoma can develop such as a rectus sheath hematoma, particularly if the patient is on atiplatelet or anthithrombotic therapy.
nl:Intramusculair no:Intramuskulær injeksjon sl:Intramuskularna aplikacija