Opioid analgesics

Pain: is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage .
This implies that the degree of pain experienced by the patient may be unrelated to the extent or presence of underlying tissue damage and that emotional or spiritual distress can add to the patient s experience of pain.
Nociception: physiological process by which pain is perceived.
Hyperalgesia: an increased amount of pain associated with a mild noxious stimulus.?
Allodynia : pain evoked by a non-noxious stimulus or spontaneous pain without any?precipitating?stimulus.
Analgesia : reduction in pain sensation.
An analgesic: defined as a drug that relieves pain.Analgesics classified as:
1- opioids
2- non-opioids, e.g. nonsteroidal anti-inflammatory drugs (NSAIDs).
3- Co-analgesics or adjuvants : are drugs that have a primary indication other than pain but are analgesic in some conditions. For example, antidepressants and anticonvulsants also act to reduce nociceptive processing in neuropathic pain.
OPIOID ANALGESICS
Opioid is a generic term for natural or synthetic substances that bind to specific opioid receptors in the CNS, producing an agonist action.
Mechanism of action
Opioids act to reduce the intensity and unpleasantness of pain. They produce their effects by activating specific G protein-coupled receptors in the brain, spinal cord and peripheral nervous system. There are three major classes of opioid receptor: ?-opioid, ?-opioid and ?-opioid, which correspond respectively to their endogenous ligands, dynorphin, enkephalin and ?-endorphin.
Agonist activity at opioid receptors acts to open potassium channels and prevent the opening of voltage-gated calcium channels. This reduces neuronal excitability and inhibits the release of pain neurotransmitters.