Opioids and Analgesics

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Questions and Answers

Which of the following opioids is a partial agonist at the μ receptor and an antagonist at the κ and δ receptors?

Methadone

Buprenorphine (correct)

Pentazocine

Tramadol

What is the effect of opioid agonists on adenylate cyclase?

Increase in intracellular cAMP

Unknown effect on adenylate cyclase

No effect on adenylate cyclase

Decrease in intracellular cAMP (correct)

Which opioid receptor is involved in the suppression of N-type voltage-gated calcium channels?

μ receptor

κ receptor (correct)

δ receptor

All of the above

What is the primary mechanism of analgesia for morphine?

Stimulation of μ receptors Signup and view all the answers

Which of the following is a pure antagonist at μ, κ, and δ receptors?

All of the above Signup and view all the answers

What is the effect of opioid agonists on potassium channels?

Activation of potassium channels Signup and view all the answers

What is the effect of morphine on the cardiovascular system?

Depression of the cardiovascular system Signup and view all the answers

Which type of pain does morphine have limited effectiveness against?

Neuropathic pain Signup and view all the answers

What is dysphoria characterized by?

Restlessness and malaise Signup and view all the answers

Which receptor is responsible for respiratory depression?

μ receptors Signup and view all the answers

What is the most common cause of death in opioid poisoning?

Respiratory depression Signup and view all the answers

What is the effect of opioids on the gastrointestinal tract?

Decreases GI motility Signup and view all the answers

What is the origin of opium?

Unripe seed capsules of the poppy plant Signup and view all the answers

What is the effect of opioids on the biliary tract?

Contraction of biliary tract smooth muscle Signup and view all the answers

What binds to opioid receptors to relieve pain?

Enkephalins, endorphins, and dynorphins Signup and view all the answers

Which of the following is a effect of μ opioid receptors?

Euphoria Signup and view all the answers

What is the effect of opioids on the cardiovascular system?

Causes postural hypotension and bradycardia Signup and view all the answers

What is the effect of opioids on the respiratory center?

Inhibition of the respiratory center Signup and view all the answers

Which opioid receptor is associated with dysphoria?

κ Signup and view all the answers

Which of the following opioids is an agonist at κ receptors?

Fentanyl Signup and view all the answers

What is the effect of opioids on the pupil?

Constriction of the pupil Signup and view all the answers

What is the therapeutic use of opioids?

Relieving pain Signup and view all the answers

What is the effect of opioid receptors on the GI motility?

Inhibition Signup and view all the answers

Which of the following is a characteristic of opioid analgesics?

They are opium-like analgesics Signup and view all the answers

What happens to the urinary sphincter when it constricts?

Difficulty in urination Signup and view all the answers

What is the effect of histamine release from mast cells in the bronchi?

Bronchospasm Signup and view all the answers

What is tolerance to opioids?

Reduction in effect with repeated dosing Signup and view all the answers

What is the reason for tolerance to opioids?

Long-term desensitization or down-regulation of receptor-effector coupling mechanisms Signup and view all the answers

What does not develop tolerance to opioids?

Miosis, constipation, and convulsions Signup and view all the answers

What is psychological dependence on opioids?

The patient believes that the optimal state of well-being is achieved only through the action of the drugs Signup and view all the answers

What is the purpose of methadone in managing opioid dependence?

To substitute the opioid in use to spare the addict from undesirable withdrawal symptoms Signup and view all the answers

What is the characteristic of methadone?

It is an agonist at μ receptors and is long-acting Signup and view all the answers

Study Notes

Opioid Analgesics and Antagonists

Opioid analgesics are "opium-like analgesics" derived from the opium poppy plant (Papaver somniferum)
Opioid receptors include μ (Mu), κ (Kappa), and δ (Delta) receptors

Opioid Receptors

μ (Mu) receptor: analgesia (supraspinal level), euphoria, sedation, physical dependence, miosis
μ2 receptor: analgesia (spinal level), respiratory depression, inhibition of GI motility
κ (Kappa) receptor: analgesia (spinal level), dysphoria, psychotomimetic effect, sedation, inhibition of GI motility
δ (Delta) receptor: analgesia (spinal and affective component of supraspinal), respiratory depression, reinforcing action, inhibition of GI motility, proconvulsant action

Classification of Opioids

Agonists at μ receptors: Morphine, codeine, pethidine, oxycodone, dextropropoxyphene
Agonists at κ receptors: Fentanyl
Agonists at δ receptors: Methadone, tramadol
Mixed Agonist-Antagonists and Partial Agonists: Pentazocine (antagonist at μ receptor, agonist at κ and δ receptors), Buprenorphine (partial agonist at μ receptor, antagonist at κ and δ receptors)

Opioid Antagonists

Pure antagonists at μ, κ, and δ receptors: Naloxone, Naltrexone, Nalmefene

Mechanism of Action of Opioids

Opioid agonists bind to opioid receptors (G-protein coupled receptors) and produce the following actions:
- Inhibit adenylate cyclase → decrease in cell excitability (through μ & δ receptors)
- Activate potassium channels → hyperpolarization of neurons → decrease in neuronal excitability (through μ & δ receptors)
- Suppress N-type voltage-gated calcium channels → reduced intracellular Ca2+ → decreased release of neurotransmitters from presynaptic neurons (through κ receptors)

Pharmacological Actions of Morphine

Central Effects:
- Stimulant Effects: Analgesia, euphoria, dysphoria, sedation, respiratory depression, vasomotor center depression, cough suppression, miosis, nausea and vomiting, convulsions
- Depressant Effects: Cardiovascular system, gastrointestinal tract, biliary tract, urinary bladder, and bronchi
Peripheral Effects:
- Cardiovascular System: Postural hypotension, bradycardia, and depression of the vasomotor center in the medulla
- Gastrointestinal Tract: Increased sphincter tone, decreased GI motility, and constipation
- Biliary Tract: Contraction of biliary tract smooth muscle, biliary spasm, and increased intrabiliary pressure
- Urinary Bladder: Constriction of the urinary sphincter, difficulty in urination, and contraction of the detrusor muscle
- Bronchi: Bronchospasm due to the release of histamine from mast cells

Tolerance and Dependence

Tolerance: Reduction in effect with repeated dosing (or higher dose is required to produce the same effect)
Dependence:
- Psychological Dependence: Emotional cravings for the drug due to euphoria and pain relief
- Physical Dependence: Continued presence of the drug is needed to maintain physiological equilibrium

Management of Opioid Dependence

Methadone: Long-acting agonist at μ receptors, used to substitute for opioids to spare withdrawal symptoms
Management involves withdrawal of opioids and substitution with methadone, followed by tapering of methadone doses over weeks

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Description

This quiz covers opioid analgesics and antagonists, including their receptor selectivity, mechanism of action, and pharmacological actions. It also explores the role of drugs in opioid dependence and the use of methadone in management.