Opioid Analgesics and Antagonists — MCQs
All of the following are actions produced by mu receptors of morphine except:-
Which of the following is a pure opioid antagonist?
Which of the following is the most effective antagonist for morphine overdose?
What is the primary use of Naltrexone in the context of opioid dependence?
Morphine should not be used in the treatment of:
Antidote for opioid poisoning:
Sufentanil is classified as a potent:
Which of the following substances is not classified as an opioid?
Which of the following is the most appropriate pharmacological treatment for neuropathic pain in a diabetic patient?
A patient presented with pain in the right lower quadrant of abdomen. He has history of renal stones in right kidney. He was prescribed an opioid which is agonist at kappa receptors and antagonist at mu receptors. The likely drug given was:
Opioid Analgesics and Antagonists Indian Medical PG Practice Questions and MCQs
Question 1: All of the following are actions produced by mu receptors of morphine except:-
- A. Respiratory depression
- B. Hyperalgesia (Correct Answer)
- C. Miosis
- D. Decreased GI motility
Explanation: ***Hyperalgesia***- **Hyperalgesia** is not a direct effect of **μ-opioid receptor activation**; in fact, μ-receptor activation causes **analgesia**.- While chronic opioid use can lead to **opioid-induced hyperalgesia**, this is a complex phenomenon involving adaptations to long-term exposure, not an acute action of the receptor itself.*Respiratory depression*- Activation of **μ-opioid receptors** in the **brainstem** leads to a dose-dependent decrease in respiratory rate and depth [1].- This effect is mediated by reduced sensitivity of respiratory centers to **CO2 levels**, making it a major concern in opioid overdose [1].*Miosis*- **Miosis** (pinpoint pupils) is a classic sign of **opioid intoxication** and results from excitatory actions of μ-opioid receptor activation on the **Edinger-Westphal nucleus** of the oculomotor nerve [1, 3].- This effect is mediated through inhibition of **GABAergic neurons**, leading to increased parasympathetic outflow to the iris sphincter.*Decreased GI motility*- Activation of **μ-opioid receptors** in the **gastrointestinal tract** reduces peristalsis, increases water reabsorption, and decreases secretions [1, 2].- This leads to **constipation**, a very common and persistent side effect of opioid use [1, 2].
Question 2: Which of the following is a pure opioid antagonist?
- A. Naloxone (Correct Answer)
- B. Buprenorphine
- C. Pentazocine
- D. Morphine
Explanation: ***Naloxone*** - **Naloxone** is a pure opioid antagonist that rapidly reverses the effects of opioid agonists by competing for opioid receptor binding sites [1,2]. - It has a high affinity for μ-opioid receptors and acts as a competitive antagonist [1], making it clinically useful for treating **opioid overdose**. *Buprenorphine* - **Buprenorphine** is a **partial opioid agonist** at the μ-opioid receptor and an antagonist at the κ-opioid receptor [4]. - It can precipitate withdrawal in opioid-dependent individuals if administered while full agonists are present due to its partial agonistic activity. *Pentazocine* - **Pentazocine** is a **mixed opioid agonist-antagonist**, acting as a partial agonist or antagonist at μ-opioid receptors and an agonist at κ-opioid receptors. - Its effects can vary, including analgesia (kappa agonism) and potential for withdrawal symptoms in opioid-dependent individuals (mu antagonism). *Morphine* - **Morphine** is a potent **full opioid agonist** that primarily acts on μ-opioid receptors, producing analgesia, sedation, and euphoria [3]. - It does not block opioid receptors; instead, it activates them, leading to its therapeutic and adverse effects.
Question 3: Which of the following is the most effective antagonist for morphine overdose?
- A. Buprenorphine
- B. Nalorphine
- C. Naloxone (Correct Answer)
- D. Pentazocine
Explanation: ***Naloxone*** - **Naloxone** is a pure opioid antagonist that rapidly reverses the effects of opioid overdose by competing for and displacing opioids from the **mu-opioid receptors** - Its rapid onset of action (1-2 minutes IV) and high affinity for opioid receptors make it the drug of choice for treating **morphine overdose**, particularly in emergency settings - Has no intrinsic agonist activity, making it safe and effective for acute reversal *Buprenorphine* - **Buprenorphine** is a partial opioid agonist, meaning it produces some opioid effects but to a lesser degree than full agonists like morphine - While it can displace full agonists from receptors, it is primarily used in **opioid dependence treatment** rather than acute overdose reversal - Has a ceiling effect for respiratory depression and is not the first-line agent for emergency overdose management *Nalorphine* - **Nalorphine** is an older mixed agonist-antagonist that was historically used for opioid overdose - It has largely been replaced by **naloxone** due to its own opioid-like effects (agonist activity at kappa receptors) and less favorable side effect profile - Can cause respiratory depression itself, making it unsuitable for emergency use *Pentazocine* - **Pentazocine** is an opioid agonist-antagonist (kappa agonist, mu antagonist), meaning it acts as an agonist at some opioid receptors and an antagonist at others - This mixed action means it can precipitate **withdrawal symptoms** in opioid-dependent individuals and is not suitable for reversing a full opioid overdose - Used primarily for analgesia, not overdose reversal
Question 4: What is the primary use of Naltrexone in the context of opioid dependence?
- A. Prevent relapse (Correct Answer)
- B. Prevent respiratory depression
- C. Treatment of opioid overdose
- D. Treat withdrawal symptoms
Explanation: ***Prevent relapse*** - **Naltrexone** is an **opioid antagonist** that blocks opioid receptors, thereby preventing the euphoric and other intoxicating effects of opioids. - This action helps to reduce cravings and deter opioid use, making it a primary medication for **relapse prevention** in individuals with opioid dependence. *Prevent respiratory depression* - Preventing respiratory depression is not the primary use of naltrexone; opioid antagonists like **naloxone** are used to reverse **opioid-induced respiratory depression** in overdose situations. - Naltrexone is used for longer-term management and does not have a direct role in acute respiratory support. *Treatment of opioid overdose* - While both are opioid antagonists, **naloxone** is the drug of choice for immediate **opioid overdose reversal** due to its rapid onset and shorter duration of action. - Naltrexone has a slower onset and longer duration, making it unsuitable for acute overdose treatment. *Treat withdrawal symptoms* - **Naltrexone** is generally *not* used to treat acute opioid withdrawal symptoms because it can precipitate or worsen withdrawal by blocking opioid receptors. - Withdrawal symptoms are typically managed with opioid agonists like **buprenorphine** or other symptomatic treatments.
Question 5: Morphine should not be used in the treatment of:
- A. Cancer pain
- B. Ischemic pain
- C. Biliary colic (Correct Answer)
- D. Postoperative pain
Explanation: ***Biliary colic*** - Morphine can cause **spasms of the sphincter of Oddi**, leading to an increase in biliary pressure and potentially exacerbating the pain of biliary colic. - This adverse effect can worsen the patient's condition rather than alleviate it, making alternative analgesics like **pethidine (meperidine)** or **NSAIDs** more appropriate for biliary pain. *Cancer pain* - Morphine is a **first-line opioid** for managing moderate to severe cancer pain, providing effective analgesia as part of a comprehensive pain management strategy. - Its efficacy in cancer pain is well-established, and doses can be titrated to achieve optimal pain control without significant risk of addiction in this context. *Postoperative pain* - Morphine is widely used for **postoperative pain management** due to its potent analgesic effects and predictable pharmacokinetics. - It is effective in reducing acute surgical pain and can be administered via various routes, including intravenous and epidural, to suit patient needs. *Ischemic pain* - Morphine is effective in treating ischemic pain, particularly in conditions like **myocardial infarction**, where it helps to reduce pain, anxiety, and **myocardial oxygen demand**. - While it was favored historically because of its action as a **venodilator** and **anxiolytic**, it is now used with caution in acute coronary syndromes, specifically because it can delay the absorption of oral antiplatelet drugs.
Question 6: Antidote for opioid poisoning:
- A. Pethidine
- B. Flumazenil
- C. Naloxone (Correct Answer)
- D. Physostigmine
Explanation: ***Naloxone*** - **Naloxone** is a pure **opioid antagonist** that reverses the effects of opioid overdose by competing for and binding to opioid receptors. - It is crucial in emergent situations to restore **respiratory drive** and consciousness in patients with opioid-induced respiratory depression. *Pethidine* - **Pethidine** is an **opioid analgesic** itself, primarily used for pain management, and would worsen opioid poisoning. - It works by binding to opioid receptors, leading to centrally mediated pain relief, making it contraindicated in overdose. *Flumazenil* - **Flumazenil** is an antagonist for **benzodiazepines**, used to reverse their sedative and respiratory depressant effects. - It has no effect on opioid receptors and would not be effective in treating opioid poisoning. *Physostigmine* - **Physostigmine** is a **cholinesterase inhibitor** used to reverse anticholinergic toxicity. - It increases acetylcholine levels at the synapse and is not indicated for opioid overdose.
Question 7: Sufentanil is classified as a potent:
- A. Myocardial depressant
- B. Analgesic (Correct Answer)
- C. Hepatotoxin
- D. Anticonvulsant
Explanation: ***Analgesic*** - **Sufentanil** is a synthetic **opioid analgesic** primarily used for its potent pain-relieving effects, especially in surgical and intensive care settings - It acts by binding to and activating **μ-opioid receptors** in the central nervous system, reducing the perception of pain - Approximately **5-10 times more potent than fentanyl**, making it one of the most potent opioid analgesics available - Commonly used in **anesthesia** for its rapid onset and short duration of action *Myocardial depressant* - While high doses of some anesthetic agents can cause myocardial depression, sufentanil has **minimal direct myocardial depressant effects** in clinically relevant doses - Its primary classification is not as a direct cardiac depressant, although it can cause **bradycardia** and hypotension through **vagal stimulation** and decreased sympathetic tone *Hepatotoxin* - There is **no significant evidence** classifying sufentanil as a hepatotoxin that causes liver damage - Liver toxicity is more commonly associated with drugs like **acetaminophen in overdose** or certain anesthetics like **halothane** - Sufentanil is extensively metabolized by the liver but does not cause hepatotoxicity *Anticonvulsant* - **Sufentanil** does not possess anticonvulsant properties - Opioids generally do not have seizure prevention effects and may occasionally lower the seizure threshold, though this is rare with sufentanil at therapeutic doses - Anticonvulsants are a separate class of drugs (e.g., phenytoin, valproate, levetiracetam) used to prevent or reduce seizures
Question 8: Which of the following substances is not classified as an opioid?
- A. Heroin
- B. Ketamine (Correct Answer)
- C. Methadone
- D. Fentanyl
Explanation: ***Ketamine*** - **Ketamine** is classified as a **dissociative anesthetic** and does not act on opioid receptors. - Its primary mechanism of action involves **N-methyl-D-aspartate (NMDA) receptor antagonism**. *Heroin* - **Heroin** (diacetylmorphine) is a **semisynthetic opioid** derived from morphine [1, 3]. - It rapidly crosses the **blood-brain barrier** and is metabolized to morphine, where it acts as a potent **mu-opioid receptor agonist** [3]. *Methadone* - **Methadone** is a **synthetic opioid** used in the treatment of opioid dependence and chronic pain [1, 2]. - It acts primarily as a **mu-opioid receptor agonist** with a long duration of action [1, 2]. *Fentanyl* - **Fentanyl** is a powerful **synthetic opioid** analgesic, much more potent than morphine [2]. - It selectively binds to and activates **mu-opioid receptors**, producing strong analgesic and sedative effects [2].
Question 9: Which of the following is the most appropriate pharmacological treatment for neuropathic pain in a diabetic patient?
- A. Acetaminophen
- B. Tramadol
- C. Aspirin
- D. Gabapentin (Correct Answer)
Explanation: ***Gabapentin*** - **Gabapentin** is a widely recommended first-line treatment for diabetic neuropathic pain due to its efficacy in modulating neuronal excitability. - It works by binding to the **α2δ subunit of voltage-gated calcium channels**, reducing calcium influx and thereby decreasing the release of excitatory neurotransmitters involved in pain signaling. *Acetaminophen* - **Acetaminophen** is primarily an analgesic and antipyretic, effective for mild to moderate non-neuropathic pain. - It has no significant efficacy against **neuropathic pain**, which involves distinct neurobiological mechanisms. *Tramadol* - **Tramadol** is an opioid analgesic with some serotonin and norepinephrine reuptake inhibition, offering moderate pain relief. - While it can be used for moderate to severe pain, it is generally considered a **second-line agent** for neuropathic pain due to its opioid nature and potential side effects. *Aspirin* - **Aspirin** is a nonsteroidal anti-inflammatory drug (NSAID) primarily used for its anti-inflammatory, analgesic, and antiplatelet effects. - It is **ineffective for neuropathic pain**, which does not typically involve peripheral inflammation as its primary mechanism.
Question 10: A patient presented with pain in the right lower quadrant of abdomen. He has history of renal stones in right kidney. He was prescribed an opioid which is agonist at kappa receptors and antagonist at mu receptors. The likely drug given was:
- A. Pentazocine (Correct Answer)
- B. Tramadol
- C. Buprenorphine
- D. Fentanyl
Explanation: ***Pentazocine*** - **Pentazocine** is a **mixed agonist-antagonist opioid analgesic** that acts as an **agonist at kappa opioid receptors** and a **weak antagonist or partial agonist at mu opioid receptors**. - This unique receptor profile makes it the drug described in the question. - It is effective for **moderate to severe pain** including **renal colic** (pain from renal stones), while having a **lower abuse potential** and **ceiling effect on respiratory depression** compared to pure mu agonists. *Tramadol* - **Tramadol** is a synthetic opioid that acts primarily as a **weak mu-opioid receptor agonist** and also inhibits the reuptake of **norepinephrine** and **serotonin**. - It does **not** have significant kappa receptor agonism or mu receptor antagonism. - Does not fit the description given in the question. *Buprenorphine* - **Buprenorphine** is a **partial agonist at mu opioid receptors** and an **antagonist at kappa opioid receptors**. - This receptor activity profile is the **opposite** of what is described in the question (which asks for kappa agonist, mu antagonist). *Fentanyl* - **Fentanyl** is a highly potent **pure mu-opioid receptor agonist**. - It has **no significant kappa receptor agonism** or mu receptor antagonism. - Does not match the pharmacological profile described in the question.
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