Bntx

Levorphanol Etorphine

Naloxone Naltrexone

Enkephalin

BNTX, 7-benzylidenenaltroxone; EKC, ethylketocyclazosine; NTB, benzofuran analog of naltrindole; nor-BNI, nor-binaltorphimine. DAMGO, CTOR, DPDPE, DSLET, see Table 21-1.

BNTX, 7-benzylidenenaltroxone; EKC, ethylketocyclazosine; NTB, benzofuran analog of naltrindole; nor-BNI, nor-binaltorphimine. DAMGO, CTOR, DPDPE, DSLET, see Table 21-1.

sites. Respiratory depression and miosis may be less severe with k agonists. Instead of euphoria, k receptor agonists produce dysphoric and psychotomimetic effects. In neural circuits mediating reward and analgesia, m and k agonists have antagonistic effects (see below).

Mixed agonist-antagonist compounds were developed in the hope that they would have less addictive potential and respiratory depression than morphine and related drugs. In practice, for the same degree of analgesia, the same intensity of side effects occurs. A "ceiling effect" limits the amount of analgesia attainable with these drugs. Some mixed agonist-antagonist drugs, such as pentazocine and nalorphine, can produce severe psychotomimetic effects that are not reversible with naloxone (and thus may not be mediated via classical opioid receptors). These drugs also can precipitate withdrawal in opioid-tolerant patients, further limiting their clinical use.

Analgesia

Morphine-like drugs produce analgesia, drowsiness, changes in mood, and mental clouding. The analgesia occurs without loss of consciousness. When therapeutic doses of morphine are given to patients with pain, they report that the pain is less intense, less discomforting, or entirely gone; drowsiness commonly occurs. In addition to relief of distress, some patients experience euphoria.

When morphine in the same dose is given to a normal, pain-free individual, the experience may be unpleasant. Nausea is common, and vomiting may occur. There may be feelings of drowsiness, difficulty in mentation, apathy, and lessened physical activity. As the dose is increased, the subjective, analgesic, and toxic effects, including respiratory depression, become more pronounced. Morphine does not have anticonvulsant activity and usually does not cause slurred speech, emotional lability, or significant motor incoordination.

The relief of pain by morphine-like opioids is relatively selective, in that other sensory modalities are not affected. Patients frequently report that the pain is still present, but they feel more comfortable. Continuous dull pain is relieved more effectively than sharp intermittent pain, but sufficient amounts of opioid can relieve even the severe pain associated with renal or biliary colic.

Mood Alterations and Rewarding Properties

The mechanisms by which opioids produce euphoria, tranquility, and other mood alterations (including rewarding properties) are not entirely clear. However, the neural systems that mediate opioid reinforcement are distinct from those involved in physical dependence and analgesia. Behavioral and pharmacological data point to the role of dopaminergic pathways, particularly involving the nucleus accumbens, in drug-induced reward. There is ample evidence for interactions between opioids and dopamine in mediating opioid-induced reward (see Chapter 23).

Other Central Nervous System Effects

Whereas opioids are used primarily for analgesia, they produce a host of other effects, as summarized below. High doses of opioids can produce muscular rigidity in humans. Chest wall rigidity severe enough to compromise respiration is not uncommon during anesthesia with fentanyl, alfen-tanil, remifentanil, and sufentanil.

Baby Sleeping

Baby Sleeping

Everything You Need To Know About Baby Sleeping. Your baby is going to be sleeping a lot. During the first few months, your baby will sleep for most of theday. You may not get any real interaction, or reactions other than sleep and crying.

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