ABSTRACT
The drug formed not only has less or no analgesic activity but, in addition, has actions that 'antagonize' those of the original narcotic when an opioid's biochemical structure is modified by substitution of the methyl group attached to the tertiary nitrogen. These drugs are termed narcotic antagonists. This chapter focuses on agonist effects of those drugs with the view toward developing antagonists with potent agonist activity able to be effective analgesics without the accompanying risk of physical dependence. Narcotic antagonists with predominant agonist effects may actually suppress withdrawal in persons on low doses of morphine while precipitating withdrawal only in individuals maintained on high doses. These drugs act as an agonist at one receptor and an antagonist at another. Pentazocine, cyclazocine, nalorphine, and nalbuphine block the mu receptors while others such as buprenorphine are partial agonists. The greatest advantage of agonist-antagonists seems to be the small volume of solution injected to achieve satisfactory analgesia.
