Influence of injection site and route on medication absorption

Concerns related to drug absorption are not limited to the oral route of administration. Medications given by various parenteral routes must also be absorbed to gain access to the systemic circulation. This article reviews the absorption characteristics of commonly administered medications by type and site of injection. The article focuses on four routes of parenteral injections: intramuscular, intralipomatous, subcutaneous, and intradermal. Differences in absorption relative to route or site of injection have been often demonstrated in studies, when such information was actively sought. Particularly important differences have been found with members of the following classes of medications: opiates, benzodiazepines, vaccines, insulins, and antiarrhythmics.