Analgesia opioid addict

There are various opioid receptors the three major classes of opioid receptors are mu (p), delta (5) and kappa (k) receptors. The p, receptor is the principal pain-modulating site in the CNS, mediating the action of morphine. There is considerable interest in the K receptor, which mediates a sedating analgesia with decreased addiction liability and respiratory depression and which allows for some structural flexibility. Unfortunately, the K receptor seems to be coupled to the sigma (a) receptor, which is implicated in psychotomimetic and dysphoric side effects. 

Suppression of cough can be obtained at doses lower than those needed for analgesia. However, in recent years the use of opioid analgesics to allay cough has diminished largely because a number of effective synthetic compounds have been developed that are neither analgesic nor addictive. These agents are discussed below. 

The opioid analgesics are among the most effective drugs available for the suppression of cough. This effect is often achieved at doses below those necessary to produce analgesia. The receptors involved in the antitussive effect appear to differ from those associated with the other actions of opioids. For example, the antitussive effect is also produced by stereoisomers of opioid molecules that are devoid of analgesic effects and addiction liability (see below). 

In an effort to develop opioid analgesics with a reduced incidence of respiratory depression or propensity for addiction and dependence, compounds that show preference for >ropioid receptors have been developed. Butorphanol and nalbuphine have shown some clinical success as analgesics, but they can cause dysphoric reactions and have limited potency. Interestingly, butorphanol has also been shown to cause significantly greater analgesia in women than in men. The reason for this difference is not known. 

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