Pain and Pain management (lab. paper)

Pharmacology

Pain and Pain management
Pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.
Serves biological functions, warning of external danger, e.g. excessive heat or physical trauma, and internal pathology, e.g. inflammation or blockage of a ureter by a kidney stone, enabling avoidance or treatment. It is inherently self-limiting when the provoking source removed.
Types of pain
1-Acute pain usually has a readily definable cause Its biological function is protective, acting as a warning that an external threat is noxious, or signaling organ malfunction. It has a well-defined time of onset, often associated with
Signs of hyperactivity of the autonomic nervous system, e.g. tachycardia, hypertension and pallor,
2-Chronic pain usually considered pain that has lasted for longer than 6 months. It does not signify a danger that requires immediate avoidance and a patient may not interpret such pain as indicating serious disease.

Pain receptors and fibers
Two main groups of skin receptors have been identified:
• High-threshold mechanoreceptors (HTMs),which detect local deformation, e.g. touch.
• Polymodal nociceptors, which detect a variety of types of injury (e.g. heat) and noxious (harmful) stimulation. These do not have a specialized structure and are simply bare nerve endings in the periphery.

Neurotransmitters involved in pain
Inhibitory neurotransmitters
Several families of endogenous opioids have been identified including the endorphins,enkephalins and dynorphins. Each family derived from a distinct precursor polypeptide and has a characteristic anatomical distribution.


Stimulatory transmitters and mediators
Physical or chemical insult can stimulate nociceptors. Inflammation, ischemia or other pain inducing stimuli cause the release of noxious chemicals (e.g. bradykinin, histamine and 5-HT) in injured tissues. Prostaglandins (PGs), although not directly producing pain, appear to sensitize nociceptors to various chemical and pressure stimuli.

Medications to control pain

1- Anesthetic agents [general and local anesthetics].
2- Analgesic agents: NSAID & opioids
3- Adjuvant analgesics

Analgesic adjutants

These include three types of agent:
• Co-analgesics (secondary analgesics), for example an anticonvulsant, e.g. clonazepam, gabapentin or pregabalin, or a low-dose tricyclic antidepressant, e.g. amitriptyline.
• Other psychotropic agents, e.g. normal dose antidepressants, to treat the depression that frequently accompanies moderate to severe chronic pain.
• Corticosteroids, e.g. dexamethasone, to reduce edema around a tumor and so prevent pressure on adjacent nerves or other tissues.