Tripoli University Faculty of Pharmacy Drug Treatment of Pain 2011-2012 BYPROF. ABDALLA SALEM ELHWUEGI (Ph.D.)
Main Goals• To know mechanisms and pain pathways.• To know Classification of analgesics.• To know about narcotic analgesics (M.O.A., PA, S.E., C.I., T.U., Tolerance and Dependence to opioids).• To know about non-narcotic analgesics (M.O.A., PA, S.E., C.I., T.U.)
Peripheral and central Pain pathways • When a pain-producing stimulus activates the primary afferent nociceptor, it generates electrochemical impulses that propagate through the peripheral nerves to activate spinal cord nerve cells. These nerve cells in turn give rise to the pathways that conduct the pain message to higher centers in the thalamus and cerebral cortex that are required for the conscious perception of pain.
Role of the Brain in NociceptionThe brain is vital for 3 aspects of pain:1. Perception of pain and its characteristics (sensory-discrimination).2. Reaction to pain (emotional aspects of pain-affective-motivational).3. Modulation of pain (especially by descending control).
Types of Pain Acute Pain Chronic Pain1. An unpleasant sensory 1. Pain in the absence of or or emotional experience following the removal of a2. Caused by tissue injury. noxious stimulus. This is also known as It is also known as "pathological pain". "physiological" or 2. The presence of chronic "nociceptive" pain. pain implies a lesion or3. Has a a role in malfunction in the "pain protecting the organism pathway". from injurious stimuli 3. Chronic pain has no (noxious). protective role and is a disease process.
Mechanisms of Pain Relief1. Membrane lipid/protein disruption - general anesthetics.2. Ion channel blockade - local anesthetics.3. GABA receptor modulation - general anesthetics, IV anesthetics.4. “Opioid” receptor activation - Narcotic analgesics5. Enzyme inhibition – Aspirin Like drugs (NSAIDs).
Treatment of Pain Drugs Known as analgesics Types of Analgesics• Opioid Analgesics • Non-opioid Analgesics • Morphine like • Aspirin like • Non-steroidal anti- inflammatory (NSAIDS)
I) Narcotic Analgesics & Narcotic Antagonists• Narcotic analgesics are those agents that are distinguished from agents such as aspirin in that they are used clinically for severe visceral pain and possess an dependence (addiction) liability.
Classification Of Opioids1. Classification based on Source• Naturally occurring from the exudate of the seed pod of the opium poppy. Contains over 20 alkaloids including morphine and codeine (opiates).• Commercial synthesis of compounds with varying therapeutic properties.• Endogenous Opiate Peptides - Endorphines (Enkephalins, Beta-endorphin and Dynorphins).
2. Classification based on action at opioid receptors Compound Mu Delta Kappa (μ) (δ) (κ) Morphine Ag Ag Ag Fentanyl Ag Ag Ag Methadone Ag Pentazocine HCl pAg Ag Butorphanol pAg Ag tartrate Nalbuphine HCl pAg Ag Buprenorphine HCl pAg Naloxone HCl Ant Ant AntAg (Agonist) Ant (Antagonist) pAg (Partial agonist)
Examples• Opioid drugs that are full agonists at mu receptors: “morphine met me finally”:(Morphine, methadone, meperidine, fentanyl)• Opioid drugs that are partial agonists at mu receptors: “partially b-blocks narcotics”:(pentazocine, butorphanol, buprenorphine, nalbuphine).
The “Opioid” ReceptorsA. Characteristics• High concentrations of these receptors are located in areas of the CNS known to involve pain signal transmissioni. The dorsal horn of the spinal cordii. Periaqueductal grayiii.Rostral ventral medulla, and several thalamic nuclei• Selective binding sites for the opioids.• Binding of Opioids to these receptors mediate diverse pharmacological effects.
B. Properties• Structural specificity - small modifications of the drug molecule cause large changes in drug binding (and in drug effect in vivo).• Stereospecificity - only the l (-) isomeric form of the agent binds with high affinity (and is active as an analgesic).• Competition between agonists and antagonists - drugs of partially similar structure can bind to the receptor and block binding of agonists such as morphine.• Reversibility - bound drug can be displaced from the receptors by an excess of other molecules that possess binding affinity.• Binding affinity vs. potency - a good correlation exists between the affinity for binding to the receptors and potency of agonist or antagonist in vivo.• All three major receptors are members of the G-protein-coupled family of receptors.