Questions
[1] Morphine produces analgesia through which of the following actions?
- Activation of neuronal adenylyl cyclase
- Increased prejunctional neurotransmitter release
- Reduction of postjunctional neuronal potassium conductance
- Reduction of prejunctional neuronal calcium conductance
[2] Which of the following opioid agonists is not metabolized to an active agent with analgesic activity?
- Morphine
- Codeine
- Heroin
- Meperidine
[3] Which of the following is true of the antitussive agent dextromethorphan?
- It activates mu, delta, and kappa receptors
- It has analgesic activity in addition to its antitussive activity
- It has no dependence liability
- It is more constipating than codeine
Answers
[1] D. Opioid agonists bind to G-protein-coupled receptors to reduce adenylyl cyclase activity, to reduce prejunctional calcium conductance, which results in a decrease in neurotransmitter release, and to enhance postjunctional potassium conductance, which results in decreased responsiveness to excitatory neurotransmitters.
[2] D. Meperidine is metabolized to normeperidine that may result in seizures. Morphine is metabolized to morphine-6 glucuronide. Codeine and heroin are metabolized, in part, to morphine.
[3] C. Dextromethorphan is a nonopioid drug that is nearly as effective as codeine as an antitussive agent but with less constipating effect. It has no analgesic activity or dependence liability.
Pharmacology pearls
Seeking the relief of pain is one of the most common reasons for patient visit.
Up to 75 percent of hospitalized patients who receive opioids for their pain still report severe or moderate distress as result of under-dosing, often because clinicians are afraid of causing physical dependence or addiction.
A patient, particularly a terminally ill patient, should never agonize or wish for death because of a physician’s reluctance to use adequate doses of opioids!
Seizures may occur in patients with renal failure because of the action of the morphine metabolite morphine-3-glucuronide.
An accentuated action of morphine may occur in patients with renal failure as a consequence of the action of the active morphine metabolite morphine-6-glucuronide.
Continuation:
Opioid overdose
Opioid overdose: Class
Jennifer is a clinical pharmacologist. She helps doctors of all medical specialties choose medications. Jennifer consults about drug dosage, interactions, and side effects.