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Questions and Answers
What is a significant characteristic of Naloxone?
What common side effect is associated with opioid use?
What is the recommended dose range for Pethidine when used as an analgesic?
Which opioid is commonly combined with Paracetamol for analgesic purposes?
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What is a notable effect of Pentazocine compared to morphine?
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What is the primary purpose of opioid analgesics in medical practice?
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Which of the following is classified as a natural opium alkaloid?
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What happens to the intracellular calcium levels when opioids act on their receptors?
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Which of the following is a semi-synthetic derivative of opium?
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What effect does morphine have on respiration?
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Which receptors are primarily involved in the mechanism of action of morphine?
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What sensation is often produced shortly after a rapid intravenous injection of morphine?
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Which of the following is an example of a mixed agonist-antagonist opioid?
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What is the primary cause of death due to morphine poisoning?
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Which effect does morphine have on the cough center?
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What happens to gastric emptying time when morphine is administered?
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Which of the following is NOT a symptom of acute morphine poisoning?
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What is the role of Naloxone in acute morphine poisoning?
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Which pharmacokinetic property of morphine affects its absorption?
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What physiological response does morphine induce in the vagal center?
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Which of the following adverse effects is associated with morphine use?
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Study Notes
Opioids
- Opioid analgesics are some of the oldest pain relief remedies
- The term "opiate" refers to natural or semi-synthetic narcotic alkaloids derived from opium poppy.
- The term "opioid" refers to fully synthetic or semi-synthetic narcotic alkaloids that mimic the properties of opiates and have no natural origin.
Opium
- Opium is a dark brown gummy exudate obtained from the poppy capsule (Papaver somniferum).
- Opium has been used since 4000 BC.
Opioid Classification
- Opioids can be classified based on receptor occupation:
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Agonists: Bind to opioid receptors and activate them, leading to effects like pain relief, euphoria, sedation, and respiratory depression.
- Natural opium alkaloids: Morphine, Codeine.
- Synthetic opioids: Pethidine, Methadone.
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Antagonists: Block opioid receptors, reversing the effects of agonists.
- Naloxone, Naltrexone.
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Mixed agonist-antagonists: Act as both agonists and antagonists at different opioid receptors.
- Pendazocine, Nalpurine, Butorphanol, Buprenorphine, Nalorphine
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Agonists: Bind to opioid receptors and activate them, leading to effects like pain relief, euphoria, sedation, and respiratory depression.
- Opioids can also be classified by their source:
- Natural opium alkaloids: Morphine, Codeine, Noscapine
- Semisynthetic derivatives: Heroin, Oxymorphone, Pholcodeine
- Synthetic opioids: Pethidine, Methadone, Loperamide, Fentanyl
Morphine
- Morphine is the most important alkaloid of opium.
- Many new opioids with actions similar to morphine have been synthesized.
Mechanism of Action of Opioids
- Opioids produce their effects by acting on specific opioid receptors: mu(µ), kappa(k), and delta(δ).
- These receptors are present in the central nervous system (CNS) and other tissues.
- Stimulation of opioid receptors leads to a decrease in intracellular calcium, which in turn, decreases the release of neurotransmitters.
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In the CNS:
- Stimulation of opioid receptors (e.g., by morphine)
- Decrease in intracellular calcium level
- Decrease in neurotransmitter release
- Reduced visceral pain
Pharmacological Action of Morphine
- Analgesia: Morphine provides potent pain relief without causing loss of consciousness. It can effectively manage severe pain, such as biliary colic.
- Euphoria, sedation, and hypnosis: A rapid intravenous injection of morphine can lead to a warm flushing of the skin and a pleasurable sensation in the lower abdomen. It can also cause drowsiness, a calming effect, difficulty concentrating, and detachment from surroundings.
- Respiration: Morphine produces respiratory depression by directly depressing the respiratory center in the brainstem. Morphine poisoning is often fatal due to respiratory arrest.
- Cough center: Morphine directly suppresses the cough center, reducing coughing. Opioids should primarily be used as antitussives in cases of dry cough.
- Nausea and emesis: Morphine directly stimulates the chemoreceptor trigger zone (CTZ) in the medulla, causing nausea and vomiting. However, at high doses, it can also suppress the vomiting center, resulting in no vomiting during poisoning.
- Pupils: Morphine constricts the pupils, causing a characteristic pinpoint pupil, especially at high doses.
- Vagus: Morphine stimulates the vagal center, leading to bradycardia (slow heart rate).
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Cardiovascular system: Therapeutic doses of morphine can cause hypotension due to:
- Direct peripheral vasodilatation
- Inhibition of baroreceptor reflexes
- High doses of morphine can cause depression of the vasomotor center and histamine release, both contributing to a drop in blood pressure.
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Gastrointestinal tract (GIT): Morphine significantly decreases the motility of the gut.
- Stomach: Gastric motility is decreased, leading to a prolonged gastric emptying time. Gastric acid secretion is also reduced.
- Intestine: Morphine diminishes all secretions and delays digestion.
Pharmacokinetics of Morphine
- When given orally, morphine absorption is slow and incomplete.
- Morphine undergoes first-pass metabolism in the liver.
- Morphine is well absorbed orally, metabolized in the liver, and excreted by the kidneys.
Adverse Effects of Morphine
- Nausea and vomiting
- Respiratory depression
- Dysphoria (state of being unhappy)
- Dizziness
- Hypotension
- Skin rashes
Tolerance and Dependence of Morphine
- Tolerance is the body's ability to endure or become less responsive to a substance.
- The lethal dose of morphine is 250 mg, but addicts can tolerate grams of morphine.
- Opioids such as morphine produce both psychological and physical dependence.
Management of Opioid Addiction
- Morphine is gradually withdrawn over several days and replaced with oral methadone.
- Methadone is then gradually withdrawn.
Acute Morphine Poisoning
- Symptoms include respiratory depression, pinpoint pupils, hypotension, shock, coma, and death.
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Treatment includes:
- Positive pressure respiration
- Maintenance of blood pressure
- Gastric lavage with potassium permanganate to remove unabsorbed drug
- Naloxone (0.4 to 0.8 mg IV, repeated every 10 to 15 minutes) is the specific antidote.
Other Opioids
- Heroin: Metabolized to morphine in the body. It has higher lipid solubility, leading to faster and more intense euphoric effects. It's used as an analgesic but banned in most countries.
- Codeine: Commonly used for cough suppression. It's also available with paracetamol for pain relief.
- Dextromethorphan: Acts centrally to increase the threshold for coughing. Effective as an antitussive, similar to codeine.
- Tramadol: A relatively weak opioid agonist; an effective analgesic.
- Pethidine: Causes corneal anesthesia. It has anticholinergic effects, leading to dry mouth and blurred vision. It's used for pain relief, especially visceral pain. It's also given as a pre-anesthetic medication. Adverse effects are similar to morphine.
Opioid Antagonists
- Naloxone: A pure opioid antagonist with no significant agonist activity. It can reverse the effects of morphine, especially respiratory depression, sedation, and can also precipitate morphine withdrawal syndrome. Given orally, it undergoes first-pass metabolism, so it's typically administered intravenously.
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Uses:
- Drug of choice for morphine overdose.
- Can be used to diagnose opioid dependence.
Mixed Agonist-Antagonists
- Pentazocine: Similar to morphine in its action.
- 20 mg of pentazocine is equivalent to 10 mg of morphine in analgesia.
- Sedation and respiratory depression are less pronounced.
- Doses: 50-100 mg oral, 30-50 mg IM.
- Uses: Used as opioid analgesics, especially for post-operative and chronic pain.
- Adverse Effects: Sedation, sweating, anxiety, hallucinations.
General Considerations
- Respiratory monitoring: Respirations should be carefully monitored in patients receiving opioids.
- Tolerance: Watch for signs of tolerance in patients receiving long-term opioid therapy.
- Antidote: A specific antidote (Naloxone) must be readily available in case of emergency.
Common Side Effects of Opioids
- Nausea and vomiting
- Constipation
- Itching
- Sleepiness
- Slowed breathing
- Impaired motor skills, thinking, or judgment
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Description
Explore the world of opioids, their classifications, and the historical use of opium. This quiz covers natural and synthetic opioids, their effects, and the distinctions between agonists and antagonists. Test your knowledge of these critical pain relief substances.
