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Pharmacology and Toxicology
PHAR 100
Hisham Elbatarny

Narcotic Analgesics (opiates, opioids) Outline • Introduction • History • Opioid receptors ◦ mu, kappa, delta • Pharmacokinetics • Mechanism ofAction • Pharmacological Effects • Tolerance and Dependence • Treatment • Review: Chapter 10 • morphine: benchmark analgesic Terms & Definitions • pain: highly undesirable and unpleasant sensory and emotional experience associated w/ actual or potential tissue damage • opiates/opioids: natural or synthetic drug that exerts actions on the body similar to morphine • endorphin: endogenous substance that exhibits the pharmacological properties of morphine (enkephalins, dynorphins, beta endorphins) • analgesia: pain relief • analgesic: an agent that relieves pain Types of Pain Acute • short-term • uncomfortable or hurtful sensation • typically sharp, fast pain • biologically desirable because functions as a warning signal Chronic • long-term • uncomfortable or hurtful sensation • persistent • dull, throbbing pain • no useful purpose ◦ can occur comorbidly with anxiety and depression Types of Pain Relievers Natural • main source is the poppy (Papaver somniferum) • two active ingredients: morphine and codeine • morphine comes from Morpheus (god of dreams) • morphine and codeine are legal Semisynthetic • heroin is made by adding two acetyl groups to morphine ◦ diacetylmorphine or diamorphine • heroin is 10 times more lipid soluble • heroin is illegal Types of Pain Relievers Synthetic • drugs that have little chemical resemblance to morphine, but similar effects • Meperidine (Demerol) is similar to morphine, but shorter acting • Methadone (Dolophine) and LAAM (1-alpha-acetylmethadol) • MPTP story (pharmacology gone bad!) Antagonists • Naloxone blocks the action of any opioids History • opium use has been dated back to the sixth millennium B.C. ◦ Roman physicians also prescribed it for treating diseases of the eye and diarrhea ◦ Chinese smoked opium in their pipes (“Pipe Dreams”) • Opioid use grew over the 17th, 18th and 19th century ◦ most popular use was a mixture called laudanum (something to be praised)– opium dissolved in alcohol • around this time morphine became available ◦ “The army disease” or “soldier’s disease” during the civil war (self-administration via injection) History (Heroin) • invented in 1898 by Heinrich Dreser ◦ added an acetyl group to morphine (diamorphine) • early tests showed Heroin to be more effective analgesic than morphine, with fewer side effects • sold freely and claimed to be non-addictive • 1920’s heroin use was associated with crime and it was later banned • no benefits over morphine and greater dependence liability ◦ high lipid solubility – rapid onset ◦ how often have to take drug ◦ frequency of administration ◦ social factors How do we perceive pain? Pain Transmission Pain Transmission • sensory nerve transmits painful stimuli to the brain by releasing nociceptive neurotransmitters: ◦ Substance P ◦ L-Glutamate ◦ Calcitonin gene-related peptide (CGRP) • various drugs can mimic the analgesic actions of endogenous endorphins and morphine • inhibit release of pain-inducing transmitters in the dorsal horn of the spinal cord Opioid Receptors • 1973: Opioid receptors identified in rat brain • endogenous opioids were suspected (enkephalins, dynorphins, beta endorphins) • endogenous opioid: neuromodulators (interfere with release of nts) • accentuate effect of endorphins • opioid receptors have also been found in areas outside the nervous system ◦ intestines (constipation) Opioid Receptors • Three types of opioid receptors: ◦ mu (μ): all types of pain → main receptor to which morphine binds ◦ kappa (κ): low intensity thermal and mechanical pain ◦ delta (δ): thermal and mechanical pain (modulate mu activity) • receptors differ in their distribution and affinity for endogenous opioids ◦ spinal cord has all three • mu agonists are the strongest and have the highest abuse potential • delta and kappa have little to no addictive potential Pharmacokinetics • morphine is not rapidly absorbed from the digestive tract ◦ slowly absorbed following oral administration ◦ subjected to significant first-pass effect: as drug absorbed and passes through liver is bio- transformed → about 50% removed by liver • intravenous is typical ◦ w/ the onset of AIDS, injection has become less popular, sub cut used clinical as well as IV. • antagonists are poorly absorbed by the digestive system and are usually injected • advantages of direct administration into the spinal cord ◦ prevent CNS effects (drowsiness, respiratory depression) ◦ prevent PNS effects (constipation) Pharmacokinetics • readily pass the placental barrier ◦ less effective at passing the blood-brain barrier due to poor lipid solub
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