Intramuscular drug delivery

Abstract

Administration of drugs by the intramuscular route consists of the injection of a pharmaceutical dosage form (solution, suspension, or emulsion), through the skin, into a muscle of the body. It is among the parenteral routes of drug administration and is often abbreviated IM administration.This administration route is, together with the subcutaneous (SC) and the intravenous route (IV), one of the three most used parenteral routes of drug administration. They share the common feature of invasiveness, since administration is always performed through the skin, by means of a needle or a cannula. However, only the IV route delivers the drug directly into the bloodstream. SC and IM administration, on the other hand, inject the dosage form into some tissue (subcutaneous fat or a muscle, respectively) from which the drug must be absorbed to reach systemic circulation.For systemic drug effects, the oral route is always preferred, as it is the physiological way of incorporating substances (e.g., nutrients) to the body. However, both extravascular parenteral routes (SC and IM) may become the first choice in the following situations: when the oral route is not available (e.g., unconscious patients), when the drug is chemically unstable in the gastrointestinal (GI) tract, when the drug cannot be absorbed through the intestinal mucosa, and/or when a prolonged action is desired (depot formulations). On the other hand, while SC is preferred for patient self-administration (e.g., insulin), IM is the first choice for a faster onset of action and/or for the administration of larger volumes (e.g., antibiotics, corticosteroids).As regards to the associated risks, IM drug administration is usually considered to be safer than IV administration. Application errors, however, can lead to the formation of blood clots, abscesses, and scars and even produce nerve damage (e.g., to the sciatic nerve) with the possibility of paralysis [1]. It is also important, whenever possible, to avoid the administration of large volumes by IM route, since local damage or muscle infarction may occur. A maximum value of 5 mL is generally accepted for a single IM injection to an adult, with smaller values being used for pediatric, elderly, and/or adult patients with less muscle mass. The main precaution when administrating an IM injection is to avoid entering a blood vessel (especially an artery), which could lead to the infusion of a toxic agent or a toxic vehicle directly into the intravascular space. This can usually be prevented if, immediately after inserting the needle into the muscle, the plunger is gently pulled back. If the needle pierced a blood vessel, blood will appear in the syringe. Like any parenteral route, it is important to minimize the risk of infection during administration. Products intended for IM administration must be sterile, and adequate precautions are essential to ensure sterility prior to injection. On the other hand, since microorganisms may exist on the patient?s skin, particularly if hygiene is poor, it should always be remembered to previously disinfect the area with alcohol or another disinfectant product.