Fig. 2. Schematic of the circulatory system to depict different drug distribution effects from various administration methods.

A Oral administration is the most common and simplest method for analgesic delivery to date, however, first pass metabolism limits bioavailability to the active site and exposes even healthy tissue to the drug, therefore making it inefficient and uneconomical. Both (B) injectable (mainly subcutaneous or intramuscular) and (C) implantable controlled delivery methods afford a more localized exposure of the drug when administered, especially when impregnated into a controlled release matrix. If implanted at the site of injury, therapeutic effects should stay localized to a radius relative to the site of insertion, which will depend on the system itself (i.e., drug solubility and absorption).