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Pharmacology => Drug => Narcotics
Narcotics
Narcotics, term originally applied to all compounds that produce insensibility to external stimuli through depression of the central nervous system, but now applied primarily to the drugs known as opiates-compounds extracted from the opium poppy and their chemical derivatives. Also classed as narcotics are the opioids, chemical compounds that are wholly synthesized, but which resemble the opiates in their actions.
The most important attribute of narcotics is their capacity to decrease pain, not only by decreasing the perception of pain, but also by altering the reaction to it. Although they do have sedative properties when used in large doses, they are not used primarily for sedation.
The major constituent of opium and the prototype of all narcotic analgesics is morphine, which was isolated and chemically analyzed by the German apothecary F. W. A. Setürner between 1805 and 1817. Other narcotics used in the U.S. are meperidine (trade name Demerol), codeine, and propoxyphene (trade name Darvon). Heroin, synthesized from morphine, is a potent analgesic, but its use is forbidden in the U.S. Some of the newer synthetic compounds are 1000 to 10,000 times more potent than morphine.
In addition to their painkilling properties, the narcotic analgesics cause a profound feeling of well-being (euphoria). It is this feeling that is in part responsible for the psychological drive of certain persons to obtain and self-administer these drugs. When taken chronically in large doses, the narcotics have the capacity to induce tolerance (whereby a larger and larger dose is required by the body to achieve the same effect), and ultimately psychological and physical dependence, or addiction. In this respect they are similar to the barbiturates and to alcohol. These properties make the medical use of narcotics extremely difficult and have led to strict regulation of the prescription and dispensing of this class of drugs. Even so, they are widely abused.
The mode of action of the narcotic analgesics is still not fully understood. Recent research has determined that specific regions of the brain and spinal cord have an affinity for binding opiates, and the binding sites in the brain are in the same general areas where pain centers are believed to be. This research has also succeeded in isolating compounds, called enkephalins, that are produced in the body to reduce pain; the compounds consist of five amino acids. Apparently they can depress neurons throughout the central nervous system. They belong to a group of larger compounds called endorphins, consisting of many amino acids, that have also been isolated in the body and that are produced by the pituitary gland. Administration of endorphins, including the enkephalins, results in effects similar to those produced by opiates.
The discovery of a class of compounds that are specific antagonists to the action of the opiates has made it possible to treat opiate overdosage quickly and efficiently. The standard drug for this use is naloxone. Some of the antagonists also have opiatelike properties, and this has led to the introduction of a new class of analgesics, the mixed agonists-antagonists. It is hoped that these drugs will produce analgesia without euphoria, reducing their potential for abuse. The three drugs of this class approved so far in the U.S.-pentazocine, butorphanol, and nalbuphine-are as analgesic as morphine for many uses and induce little or no euphoria. All appear to have a lower abuse potential than morphine or propoxyphene.
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