An intramuscular (IM) injection is the preferred route of administering medication when fairly rapid-acting and long-lasting dosage of medication is required.

Some medications that are irritating to the subcutaneous tissue may be given into the deep muscle tissue.

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Injection of medication into muscle tissue forms a deposit of medication that is absorbed gradually into the bloodstream. An intramuscular injection is the safest, easiest, and best tolerated of the injection routes. Remember the following guidelines:

a. The needle should be not less than one inch in length or more than one and one-half inches long (20 to 22 gauge). A needle one and one-fourth inches long (20 to 22 gauge) is commonly used.

b. A maximum volume of medication of five milliliters per injection can be administered at one site to an adult.