Intramuscular injections are used to inject a medication or other substance directly into a muscle. Many medications, certain vitamin and mineral supplements and various vaccines are delivered intramuscularly. In some cases, intramuscular injections are preferable to other forms of drug administration. However, this type of injection does pose an increased risk of side effects and complications when compared to intravenous or oral delivery methods.
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Medications administered intramuscularly are injected directly into the centre of a specific muscle. The medication is then distributed throughout the body via the cardiovascular system. This type of injection is typically used when administering small amounts of medication, and the rate of absorption depends on the type of medication being given and the injection site.
Common sites for intramuscular injections include the deltoid, vastus lateralis and gluteal muscles. Injection site selection depends on various factors, including the type of medication, the condition being treated, the desired rate of absorption and patient or doctor preference. Medications that are often administered intramuscularly include codeine, olanzapine, diazepam, methotrexate, Streptomycin, prednisone, metoclopramide, ketamine and sex hormones. Moreover, intramuscular injection is the standard method of administration for some vaccines, such as the hepatitis A and Gardasil vaccine.
Intramuscular injections are a preferred method of delivery for many drugs as this method often provides a faster rate of absorption than subcutaneous administration. Additionally, medications injected directly into muscle are absorbed at a slower rate than medications administered intravenously, which may be preferable for pain-relieving drugs and some antibiotics.
Normal side effects of intramuscular injections include localised swelling, redness, bleeding, bruising and inflammation. Rarely, patients may have a reaction to the medication being injected. Because of this, observation of patients receiving intramuscular injections for a minimum of 15 minutes is suggested. Most complications following this type of injection result from the medication and not the actual procedure. Some patients have reported experiencing discomfort and pain following the injection. This pain may last for several hours or longer.
Some people should not receive intramuscular injections, including those with thrombocytopenia and coagulopathy, as they may result in the formation of hematomas. Another complication of intramuscular injections is the development of injection fibrosis, which may occur in people who receive frequent injections. Injection fibrosis causes an inability to fully flex the affected muscle, and typically requires surgical treatment. Improper injection technique may also lead to injection fibrosis.