The perpetual pursuit of pain elimination has been constant throughout human
history and pervades human cultures. In some ways it is as old as medicine
itself. Cultures throughout history have practiced the art of pain management
through remedies such as oral ingestion of herbs or techniques believed to
have special properties. In fact, even Hippocrates wrote about the practice of
trepanation, the cutting of holes in the body to release pain. Current therapies
for management of pain include the pervasive utilization of opioids, which
have an extensive history, spanning centuries.
There is general agreement about the appropriateness of opioids for the
treatment of acute and cancer pain, but the long-term use of these drugs for
treatment of chronic non-malignant pain remains controversial. The pros and
cons regarding these issues are beyond the scope of this review. Instead, the
purpose of this review will be directed towards the pharmacology of commonly
prescribed opioids in the treatment of various chronic pain syndromes.
Opium, derived from the Greek word for “juice,” is extracted from the latex
sap of the opium poppy (Papaverum somniferum). The juice of the poppy is
the source of some 20 different alkaloids of opium. These alkaloids of opioids
can be divided into 2 chemical classes: phenanthrenes (morphine, codeine,
and thebaine) and benzylisoquinolines (agents that do not interact with opioid
receptors).
Key words: Opioid metabolism, opioid interactions, morphine, codeine,
hydrocodone, oxycodone, hydromorphone, methadone, intractable pain,
endorphins, enkephalins, dynorphins, narcotics, pharmacology, propoxyphene,
fentanyl, oxymorphone, tramadol