Physiology and Pharmacology of Epidurally Administered Drugs

In the last few decades, epidural administration of various drugs has gained popularity and widespread clinical acceptance. Epidural administration of local anesthetics and opioids has been considered “state of the art” in acute pain management (thoracic and major abdominal surgery, labor). Its advantage is that it yields profound, long-lasting, dose-dependent analgesia, leaving other sensory and motor functions intact. It facilitates early patient mobilization and ambulation and therefore reduces the risk of postoperative thromboembolism and respiratory complications. The increment in the elderly population caused an increase in musculoskeletal and spine diseases and thus, epidural steroid injections have become highly effective for chronic pain treatment. There are many factors that have an impact on drug physiology and pharmacology in the epidural space and, therefore, can modify epidural anesthesia or the expected effect of another medication. This chapter provides insight into this complex and comprehensive topic to demonstrate a predictable pattern that can provide a safe and accurate guide to clinical practice.