Opioid Analgesics PDF

Opioid Analgesic Agents AWAD MOHAMMED ALQAHTANI BSc of Anesthesia Technology King Khalid University, Muhayil Asir  Analgesics Medications that relieve pain without causing loss of consciousness Painkillers Classification of Pain By Onset and Duration I. Acute pain I...

Opioid Analgesic Agents AWAD MOHAMMED ALQAHTANI BSc of Anesthesia Technology King Khalid University, Muhayil Asir  Analgesics Medications that relieve pain without causing loss of consciousness Painkillers Classification of Pain By Onset and Duration I. Acute pain I. Sudden in onset II. Usually subsides once treated II. Chronic pain I. Persistent or recurring II. Often difficult to treat Classification of pain according to its type, nature or location 1) Somatic: Pain originating from the skin, muscles, or connective tissues. It is typically sharp and well-localized, such as pain from a cut or bruise. 2) Visceral: Pain coming from internal organs, such as the intestines, liver, or kidneys. It is often vague and poorly localized, presenting as a deep or pressure-like discomfort. 3) Superficial:Pain caused by irritation of the skin or surface tissues, like a burn or superficial cut. It is usually sharp and easy to pinpoint. 4) Vascular: Pain resulting from blood vessel issues, often associated with problems in blood flow, such as migraine headaches or pain due to vascular occlusion. 5) Referred:Pain that occurs in a part of the body distant from the actual source of injury, such as feeling arm pain during a heart attack. Classification of pain according to its type, nature or location 6) Neuropathic: Pain resulting from nerve damage or dysfunction. It can be acute or chronic and often feels like tingling or burning, as seen in diabetic neuropathy. 7) Cancer:Pain caused by tumor growth or cancer-related treatments, such as chemotherapy. This pain is often chronic and challenging to manage. 8) Psychogenic:Pain associated with psychological factors rather than a clear physical cause. It is experienced by individuals with psychological conditions, even if there is no direct physical source. 9) Central: Pain that originates from a disruption in the central nervous system (brain or spinal cord), often appearing after an injury to the brain or spinal cord. This pain tends to be chronic and distressing.  Pain Transmission There are two types of nerves stimulated: 1) “A” fibers 2) “C” fibers  Pain Transmission These pain fibers enter the spinal cord and travel up to the brain. The point of spinal cord entry is the DORSAL HORN. The dorsal horn is a part of the gray matter in the spinal cord, located at the back section. It serves as the entry point for sensory nerve fibers that carry signals of pain, temperature, touch, and pressure from different parts of the body to the central nervous system.  Pain Transmission This gate regulates the flow of sensory impulses to the brain. Closing the gate stops the impulses. There are some factors that help close the gate, such as competing sensory stimulation (such as rubbing the skin near the site of pain), emotional state, or certain nerve signals. If no impulses are transmitted to higher centers in the brain, there is NO pain perception.  Pain Transmission Body has endogenous neurotransmitters 1) Enkephalins. 2) Endorphins. Produced by body to fight pain Bind to opioid receptors Inhibit transmission of pain by closing gate  Pain Transmission The body has a natural system to relieve pain by producing chemicals known as endogenous neurotransmitters, primarily endorphins and enkephalins. These substances are released by the brain and nervous system as a natural response to pain, stress, or even during exercise.  Opioid Analgesics Pain relievers that contain opium, derived from the opium poppy. OR chemically related to opium. Narcotics:very strong pain relievers Opioid Analgesics: Mechanism of Action Three types of opioid receptors: Mu Kappa Delta Opioid Analgesics: Mechanism of Action Bind to receptors on inhibitory fibers,stimulating them Prevent stimulation of the GATE Prevent pain impulse transmission to the brain  Opioid Analgesics Three classifications based on their actions: 1) Agonist. 2) Agonist-antagonist. 3) Partial agonist. 1) Agonist opioid Agonist opioids bind to opioid receptors in the brain and spinal cord, producing analgesia (pain relief) and often euphoria. They fully activate the receptor to which they bind. Examples: 1) Morphine. 2) Fentanyl. 3) Oxycodone. 4) Hydromorphone. 5) Methadone.  2) Agonist-antagonist These drugs haveopioid a dual action. They act as agonists at some opioid receptors while acting as antagonists at others. This means they can provide analgesic effects but may also limit the potential for abuse and respiratory depression. Examples: 1) Buprenorphine (primarily a partial agonist at the mu receptor). 2) Pentazocine. 3) Nalbuphine. 4) Butorphanol.  3) Partial agonist opioid Partial agonists bind to opioid receptors and activate them but to a lesser degree than full agonists. They can provide pain relief but may not be as effective for severe pain. They also carry a lower risk of overdose. Examples: 1) Buprenorphine (also classified as an agonist-antagonist due to its complex action). 2) Tramadol.  Summary Agonists provide maximum pain relief but have higher potential for addiction and side effects. Agonist-antagonists offer a balance, with some pain relief and reduced risk of dependence. Partial agonists provide limited analgesia and have a lower risk of overdose, making them safer for certain populations.  Antagonists Opiate Opioid antagonists such as Naloxone and Naltrexone play a vital role in managing the effects of opioids and preventing harm. These antagonists bind to opioid receptors in the body and block opioids from activating them, reversing their effects and preventing serious issues like respiratory depression, which can be life- threatening. Naloxone: used in emergency situations to reverse the effects of opioid overdose. It is fast-acting, taking effect within minutes after administration, but its effects may only last for 30 to 90 minutes. Naltrexone: Primarily used as a long-term treatment to prevent relapse in individuals recovering from opioid or alcohol dependence. It reduces cravings and has a longer duration of action compared to Naloxone. Opioid Analgesics: Therapeutic Uses Main use: to alleviate moderate to severe pain. Opioids are also used for: – Cough center suppression  Opioid Analgesics: Side Effects 1) Euphoria 2) Nausea and vomiting 3) Respiratory depression 4) Urinary retention 5) Pupil constriction (miosis( 6) Constipation 7) Itching  Opiates: Opioid Tolerance Opioid tolerance: is a physiological response that occurs with prolonged use of opioid medications. It is characterized by the body’s decreasing sensitivity to the effects of opioids, meaning that over time, a person will require increasingly larger doses to achieve the same level of pain relief (analgesia) that they initially experienced with a smaller dose. Management Strategies: Managing opioid tolerance may involve rotating between different opioids (opioid rotation), using adjuvant medications (e.g., NSAIDs, antidepressants), or non- pharmacological therapies. Additionally, healthcare providers may consider alternative pain management strategies when possible.  Opiates: Physical Dependence Physical dependence: is a condition in which the body adapts to the presence of opioids, so they are needed for the body to function normally. If opioid use is abruptly stopped, withdrawal symptoms occur. results from the nervous system’s adaptation to consistent opioid use, making the presence of the drug necessary for maintaining normal body balance. Opiates: Psychological Dependence addiction A pattern of compulsive drug use characterized by a continued craving for an opioid and the need to use the opioid for effects other than pain relief  Opiates Opioid tolerance and physical dependence are expected with long-term opioid treatment and should not be confused with psychological dependence (addiction(. Tolerance refers to the need for higher doses to achieve the same effects. Physical dependence refers to the body’s adaptation to the drug, where discontinuation leads to withdrawal symptoms.  Opiates Narcotic Withdrawal Opioid Abstinence Syndrome Manifested as: Physical Symptoms: 1) Muscle and joint pain. Psychological Symptoms: 2) Nausea and vomiting. 1) Anxiety. 3) Diarrhea. 2) Depression. 4) Excessive sweating. 3) Irritability. 5) Chills and tremors. 4) Intense drug cravings. 6) Rapid heartbeat. 7) nsomnia. 5) Difficulty concentrating. Duration of Symptoms: They start within a few hours, peak at 48-72 hours, and last from a few days to a Questions are welcome Thank You  Reference Clinical Anesthesiology 6th edition 2018 the Author ; G.Morgan. Maged Mikhail and Michael Murray, chapter 10, page : 189 – 196.