dr. yieldez bassiouni. how pain is transmitted? the injury will cause release of various pain...
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How pain is transmitted?
The injury will cause release of various pain chemical mediators like prostaglandin, histamine, serotonin, bradykinin and substance P.
These mediators will stimulate the pain receptors in the skin.
Pain signals are generated and transferred via the sensory nerve to the spinal cord to the thalamus -then the massage come out of the spinal cord and travel via motor nerve to the arm muscle, causing the arm to withdraw quickly -no sensation under the skin (subcutaneous or in muscles)
Analgesia means no pain
Analgesics are agents which relieve the pain without disturbing consciousness
Analgesics are divided in to two main classes:
1) Opioid analgesics2) Non-opioid analgesics
(analgesics-antipyretics)
Opioid Non-Opioid analgesics (analgesics-antipyretics)
Are the most powerful analgesics that can relieve any type of pain
Act mainly at the level of the cortex. CNS
Can produce addiction
Example: Morphine and codeine
Are mild analgesics that treat mild types of pain as headache…..
Act at the level of the thalamus & hypothalamus
No addiction
Example: NSAIDs e.g. salicylates, and paracetamol
Opioid AnalgesicsOpioids are drugs acting at opioid receptors, morphine is the prototype of opioid agonists.
Opioid analgesics are potent drugs which selectively depress the CNS and relieve pain.
They are mainly obtained from unripe capsules of Opium poppy plant.
OPIOIDS OPIATES derived directly from opium poppy natural or synthetic with morphin – like actionMay be narcotic or non narcotic
The important alkaloid isolated from opium is morphine. Other alkaloids isolated from opium are codeine and papaverine.smooth muschle relaxant
Examples of Opioid DrugsNatural
morphine codeine
semisynthetic heroim( methymorphinsynthetic
Pethidine 1/5 morphin activity+ less addiction or meperidine
methadone for Rx of addiction fentanyl
Opioid Receptors Opioid Receptors •Several types of opioid Several types of opioid
receptors have been receptors have been identified at various sites in identified at various sites in the nervous system and other the nervous system and other tissues.tissues.• These are Mu (These are Mu (μμ), Kappa ), Kappa
((κκ) , sigma and Delta (∂) ) , sigma and Delta (∂) receptors receptors ..
Why do we ?
It is a defensive
mechanism to removes
excessive secretions
Removes potentially
harmful foreign
substances (beneficial)In some situations, coughing can be
harmful, such as after hernia repair
surgery
Cough receptors
bronchi, diaphragm, external auditory canal, larynx, nose, paranasal sinuses , pericardium, pharynx, pleura, stomach, trachea and tympanic membrane.
Antitussives = cough suppressant
Drugs used to stop or reduce
coughing
Opioid and non-opioid
Used only for nonproductive coughNB: when pnt has productive cough, give expectorant Not antihistamine because it will dry the sputum and make it thick harder to expel (vicid)
MoA of Antitussives
1) Depression of medullary center 2) Increases threshold of the cough center3) Interruption of impulses peripherally in
the respiratory tract4) Inhibition of conduction along the motor
pathwaysWork on stretch receptors on lungs numb them inactiveSoothing effect (ex: lozanges)
1- Centrally acting Antitussives Narcotic antitussives Codeine Pholcodine Hydrocodone Non narcotic antitussives Dextromethorphan Noscapine
2- Peripheral Antitussives Inhibition of the cough receptors of
Pharynx: Larynx1Demulcents
LinctusLozengesLiquorice
2InhalationBenzoinMenthol
3Local anaesthetics on pulmonary stretch receptors of alveoli: BenzonatateLignocaine (only in special circumstances)
Narcotic AntitussivesCodeine An opium alkaloid similar to morphine less potent than morphine as analgesic and
respiratory depressant. 60% effective orally. A standard antitussive A small fraction of administered codeine is
metabolized to morphine which is responsible for analgesic effects of codeine. Euphoric effect used for sever cough of bronchogenic carcinoma
Less addictive Used limited due to SE.
MOA of Codeine: Directly suppresses cough centre in
Medulla. Suppresses cough for about 6 hrs.
Adverse effects of Codeine: In therapeutic doses minimum side effects
Sedations, nausea, constipation At higher doses respiratory depression and
drowsiness can occur. Contraindicated in asthmatic patients.
Can cause tolerance and dependance.
Pholcodeine
Pholcodeine has similar efficacy as codeine with longer duration of action of 12hrsIt has no analgesic or addiction property no euphoria
Non Narcotic Antitussives
Dextromethorphan Hydrobromide A synthetic compound. Strong and partial µ agonist. As effective antitussive as codeine. MOA:1. Controls cough spasm by depressing cough
center in medulla2. Increase the threshold for coughing
Advantages of Dextromethorphan
No effect on ciliary activity No CNS depression No addiction potential No constipation
Contraindicated in children below 6 yrs of age and also in patients taking Monoamine oxidase inhibitors.
NoscapineAn opium alkaloid No narcotic, analgesic or dependance
inducing properties. Equally effective antitussive as codeineUseful for spasmodic cough.Headache and nausea are usual side effectsContraindicated in asthamatic patients.
Peripherally acting antitussive agent are acting through inhibition of cough receptor or pulmonary stretch receptor as
Inhibition of cough receptor ofPharynx: demulcent and soothing pastilles, and
garglesLarynx: emollient and soothing spray of
menthol and eucalyptusTracheobronchial airway: inhalation of hot
steam medicated with tr. Benzoin co.
Inhibition of pulmonary stretch receptor of alveoli: benzonanatete “tesselone” Chemically related to tetracaine.MOA :Reduces the cough reflex by
anesthetizing the stretch receptors in the respiratory passages, Lungs and Pleura.stop nerve transmission to cough center.
It has some central effects also. Benzonatate begins to work within 15 to 20
minutes, and its effects last for approximately 3 hours.
Adverse effects:Headache, DizzinessNasal Congestion, burning of eyes & tightness in chest.