GABAA Receptor: Mechanism and Pharmacokinetics
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Questions and Answers

What is the mechanism of action of propofol?

  • Inhibits the function of glycine receptors
  • Increases the rate of dissociation of GABA from the GABAA receptor (correct)
  • Directly activates glutamate receptors
  • Induces the release of lysophosphatidate signaling in the brain

    • How is propofol excreted from the body?

  • By metabolic breakdown in the liver
  • Excreted by kidneys (correct)
  • Via sweat glands
  • Through bile secretion

    • What is the primary factor contributing to the rapid clearance of propofol?

  • Rapid breakdown in the stomach
  • Excretion through the skin
  • Tissue uptake and elimination in the lungs (correct)
  • High metabolism in the liver

    • Why is propofol provided in an emulsion of soybean oil and glycerol?

    <p>To improve stability at room temperature</p> Signup and view all the answers

    Which component is added to propofol to prevent bacterial growth?

    <p>Disodium edetate (Diprivan)</p> Signup and view all the answers

    What is the pH range of propofol when provided with sodium metabisulfite?

    <p>4.5-6.4</p> Signup and view all the answers

    What is the context-sensitive half-time of propofol after 8-hour infusions?

    <p>&lt; 40 minutes</p> Signup and view all the answers

    How does initial termination of action for propofol occur?

    <p>Redistribution of drug out of the central compartment</p> Signup and view all the answers

    What does propofol inhibit as part of its mechanism of action?

    <p>Glycine receptors</p> Signup and view all the answers

    Which model best describes the pharmacokinetics of propofol?

    <p>Two-compartment model with very high clearance and low k31</p> Signup and view all the answers

    What is the typical dose of propofol for induction of anesthesia in healthy adults?

    <p>2-3 mg/kg</p> Signup and view all the answers

    What is the effect of propofol on evoked potentials in the CNS?

    <p>Decreased somatosensory and motor potentials</p> Signup and view all the answers

    What is the mechanism behind the attenuation of bronchoconstriction by propofol?

    <p>Decreased serotonin levels in the area postrema</p> Signup and view all the answers

    How does propofol compare to midazolam in terms of memory impairment at equal sedation levels?

    <p>Propofol causes more memory impairment</p> Signup and view all the answers

    What is the typical dose of propofol for maintenance of anesthesia?

    <p>25-100 μg/kg/min</p> Signup and view all the answers

    What organ system experiences a 30-40% decrease in intraocular pressure with propofol induction?

    <p>Ocular system</p> Signup and view all the answers

    Which group requires a 25-50% reduction in propofol dose?

    <p>Elderly patients</p> Signup and view all the answers

    In which system does propofol induce a direct myocardial depression?

    <p>Cardiovascular system</p> Signup and view all the answers

    What is the effect of propofol on systemic blood pressure?

    <p>Decreases systemic blood pressure</p> Signup and view all the answers

    What is the primary use of propofol in induction and maintenance of anesthesia, similar to ondansetron?

    <p>Reducing postoperative nausea and vomiting</p> Signup and view all the answers

    What is the primary use of propofol in induction and maintenance of anesthesia, similar to ondansetron?

    <p>Reducing postoperative nausea and vomiting</p> Signup and view all the answers

    Which of the following is true regarding the effect of barbiturates on GABAA receptors?

    <p>They enhance the effect of GABA at low concentrations</p> Signup and view all the answers

    Which organ system effect is induced by barbiturates in terms of cardiovascular response?

    <p>Peripheral vasodilation and decreased contractility</p> Signup and view all the answers

    What is not a contraindication for the use of barbiturates?

    <p>Hypertension</p> Signup and view all the answers

    Which procedure was barbiturate use previously associated with for neuroprotection?

    <p>Temporary occlusion of cerebral arteries</p> Signup and view all the answers

    What is a mechanism of the neuroprotective effect of barbiturates?

    <p>Reverse steal (Robin Hood) effect</p> Signup and view all the answers

    What is a side effect associated with low blood levels of thiopental?

    <p>Antianalgesic effect</p> Signup and view all the answers

    What organ system effect do barbiturates cause in terms of intracerebral pressure?

    <p>Proportionally decrease intracerebral pressure</p> Signup and view all the answers

    Which condition is triggered by induction of heme synthesis and is a contraindication for barbiturate use?

    <p>Porphyria</p> Signup and view all the answers

    What is the primary route of metabolism for barbiturates?

    <p>Hepatic oxidation</p> Signup and view all the answers

    What type of dosages is required for barbiturates in premedicated patients?

    <p>Dosages should be reduced</p> Signup and view all the answers

    What is the mechanism of action of ketamine?

    <p>Inhibition of NMDA receptors</p> Signup and view all the answers

    What is the primary reason for ketamine being the drug of choice for electroconvulsive therapy (ECT)?

    <p>It has a rapid onset of action</p> Signup and view all the answers

    What is the unique characteristic of S(+) ketamine compared to R(-) ketamine?

    <p>4x greater affinity for phencyclidine binding site on NMDA receptor</p> Signup and view all the answers

    What is the effect of ketamine on the voltage gated sodium channels?

    <p>Inhibition of sodium influx</p> Signup and view all the answers

    How does ketamine produce its analgesic and amnesic effects?

    <p>Inhibition of glutamate release and NMDA receptor binding</p> Signup and view all the answers

    What is the primary route of metabolism for ketamine?

    <p>Hepatic microsomal enzymes</p> Signup and view all the answers

    What contributes to the brief duration of action of ketamine?

    <p>Redistribution to adipose tissue</p> Signup and view all the answers

    Which receptor type does ketamine NOT antagonize?

    <p>GABA receptors</p> Signup and view all the answers

    What effect does S(+) ketamine have on cognitive function compared to the racemic mixture?

    <p>Quicker return of cognitive function</p> Signup and view all the answers

    What is the most accepted form of ketamine available in Europe and not in the United States?

    <p>10% S(+) ketamine solution</p> Signup and view all the answers

    Which benzodiazepine undergoes rapid absorption from the GI tract and has a high hepatic clearance?

    <p>Midazolam</p> Signup and view all the answers

    Which benzodiazepine exhibits delayed elimination in the presence of drugs that inhibit cytochrome P450, and has a prolonged elimination in the elderly?

    <p>Midazolam</p> Signup and view all the answers

    Which benzodiazepine is insoluble in water and dissolved in organic solvents like propylene glycol and sodium benzoate?

    <p>Diazepam</p> Signup and view all the answers

    Which benzodiazepine is metabolized via hepatic oxidative reduction of the methylene group, with principle metabolites including desmethyldiazepam and oxazepam?

    <p>Diazepam</p> Signup and view all the answers

    Which benzodiazepine is relatively unaffected by inhibition of cytochrome P-450 or changes in hepatic function, and is unique for its lower lipid solubility resulting in delayed onset of effect in the CNS?

    <p>Lorazepam</p> Signup and view all the answers

    Which benzodiazepine has a primary metabolite with approximately 50% activity of the parent compound and is conjugated to 1-hydroxymidazolam glucuronide for subsequent clearance by the kidneys?

    <p>Midazolam</p> Signup and view all the answers

    Which benzodiazepine exhibits greater hemodynamic stability, delayed emergence, and reliable amnesia compared to Propofol for sedation?

    <p>Midazolam</p> Signup and view all the answers

    Which benzodiazepine has a slower onset than thiopental or propofol but provides reliable amnesia, with dose required and time of onset affected by premedication, concurrent anesthetic agents, ASA physical status classification, and age?

    <p>Midazolam</p> Signup and view all the answers

    Which benzodiazepine is unique for its lower lipid solubility resulting in delayed onset of effect in the CNS, despite having higher clearance and similar volume of distribution to Diazepam?

    <p>Lorazepam</p> Signup and view all the answers

    Which benzodiazepine is metabolized via hepatic glucuronidation to inactive metabolites that are excreted by the kidneys, and is relatively unaffected by inhibition of cytochrome P-450 or changes in hepatic function?

    <p>Lorazepam</p> Signup and view all the answers

    What is the proposed mechanism behind propofol infusion syndrome?

    <p>Poisoning of the electron transport chain by propofol or a metabolite</p> Signup and view all the answers

    Which side effect is NOT associated with propofol use?

    <p>Potentiation of neuromuscular blockers</p> Signup and view all the answers

    What is the main effect of propofol on pulmonary ventilation?

    <p>Dose dependent depression of ventilation</p> Signup and view all the answers

    Which factor may require a direct acting beta agonist during propofol anesthesia?

    <p>Increased incidence of the oculocardiac reflex during pediatric strabismus surgery</p> Signup and view all the answers

    What is the effect of propofol on IOP (intraocular pressure)?

    <p>Decreases IOP</p> Signup and view all the answers

    Which statement is true regarding propofol's effect on coagulation?

    <p>Inhibits phagocytosis and bacterial killing despite the addition of preservative</p> Signup and view all the answers

    What is the recommended handling for propofol in the ICU?

    <p>Discard tubing and unused propofol after 12 hours</p> Signup and view all the answers

    Which clinical feature is NOT associated with propofol infusion syndrome?

    <p>Hypokalemia</p> Signup and view all the answers

    What is the best described model for propofol's pharmacokinetics?

    <p>Three-compartment model</p> Signup and view all the answers

    Which statement about propofol's mechanism of action is accurate?

    <p>Enhances the affinity of the GABAA receptor for GABA at supra-clinical doses</p> Signup and view all the answers

    What is the main route of clearance for propofol?

    <p>Rapidly cleared in the liver by ester hydrolysis</p> Signup and view all the answers

    What is the primary clinical use of propofol?

    <p>Induction of anesthesia</p> Signup and view all the answers

    Which of the following is a benefit of using etomidate?

    <p>Reduces cerebral blood flow by up to 35% and decreases cerebral metabolic rate of oxygen by up to 45%</p> Signup and view all the answers

    How does etomidate affect cardiovascular function?

    <p>Has minimal effect on cardiovascular function by not significantly affecting the sympathetic nervous system or blood pressure</p> Signup and view all the answers

    What is the mechanism of action of etomidate at the γ-aminobutyric acid-A (GABA) receptor?

    <p>Acts as a positive allosteric modulator, increasing the affinity of the receptor for GABA and resulting in increased chloride conductance and hyperpolarization of the postsynaptic cell membrane</p> Signup and view all the answers

    Which property does etomidate possess in relation to seizure threshold and neuroprotection?

    <p>Increases seizure threshold to local anesthetic exposure and has neuroprotective activity</p> Signup and view all the answers

    What is the effect of etomidate on the respiratory system?

    <p>Produces a dose-related central respiratory depression with decreased ventilatory response to CO2 and decreased hypoxic drive to ventilation</p> Signup and view all the answers

    What pharmacological property do etomidate derivatives have compared to etomidate?

    <p>Different structures and pharmacological properties compared to etomidate</p> Signup and view all the answers

    What is a side effect associated with the administration of etomidate?

    <p>Excitatory activity, including myoclonus and hiccups, and a high incidence of postoperative nausea and vomiting (PONV)</p> Signup and view all the answers

    In what way does flumazenil act as a benzodiazepine receptor ligand?

    <p>Acts as a competitive antagonist, preventing or reversing the effects of other benzodiazepines in a dose-dependent manner</p> Signup and view all the answers

    What is one of the uses of flumazenil?

    <p>Reversing residual benzodiazepine-induced sedation and suspected benzodiazepine overdose</p> Signup and view all the answers

    What is the effect of flumazenil on benzodiazepine-induced sedation?

    <p>Prevents or reverses benzodiazepine-induced sedation in a dose-dependent manner</p> Signup and view all the answers

    Study Notes

    • Etomidate is a sedative-hypnotic drug that can benefit patients with compromised cardiovascular status, questionable intravascular volume status, or elevated intracranial pressure (ICP).
    • Etomidate improves cerebral oxygen supply-to-demand ratio and reduces cerebral blood flow by up to 35%, while reducing cerebral metabolic rate of oxygen by up to 45%.
    • Etomidate maintains or improves cerebral perfusion pressure and reduces intracranial pressure due to decreased cerebral blood flow.
    • Etomidate is useful in mapping seizure foci during ablative procedures and may prolong seizure duration during electroconvulsive therapy.
    • Etomidate has minimal effect on cardiovascular function as it does not significantly affect the sympathetic nervous system or blood pressure.
    • Etomidate has fewer respiratory depressant effects than other induction agents, with less depression of ventilation and a decreased ventilatory response to CO2.
    • Etomidate inhibits cortisol and mineralocorticoid production for up to 72 hours after a single induction dose, but does not significantly inhibit steroidogenesis as a sedative-hypnotic.
    • Etomidate derivatives, such as methoxycarbonyletomidate and carboetomidate, have different structures and pharmacological properties compared to etomidate.
    • Etomidate can cause excitatory activity, including myoclonus and hiccups, and has a high incidence of postoperative nausea and vomiting (PONV) when given with narcotics.
    • Etomidate acts as a positive allosteric modulator of the γ-aminobutyric acid-A (GABA) receptor, increasing the affinity of the receptor for GABA and resulting in increased chloride conductance and hyperpolarization of the postsynaptic cell membrane.
    • Etomidate is highly protein-bound, has a similar volume of distribution to other benzodiazepines, and has a rapid clearance rate.
    • Etomidate has anxiolytic, sedative, anticonvulsant, skeletal muscle relaxation, and amnesic properties, and is used for various indications including seizure activity, delirium tremens, skeletal muscle relaxation, insomnia, anxiety, and nausea/vomiting prophylaxis.
    • Etomidate can increase seizure threshold to local anesthetic exposure and has neuroprotective activity, but these effects are not well-documented in humans.
    • Etomidate can cause a modest decrease in blood pressure primarily due to decreased systemic vascular resistance, and produces a dose-related central respiratory depression with decreased ventilatory response to CO2 and decreased hypoxic drive to ventilation.
    • Etomidate can cause apnea in large doses and has minimal musculoskeletal effects, as skeletal muscle relaxation occurs via interaction with spinal interneurons, not at the neuromuscular junction.
    • Flumazenil is a benzodiazepine receptor ligand that acts as a competitive antagonist, preventing or reversing the effects of other benzodiazepines in a dose-dependent manner.
    • Flumazenil has a rapid clearance rate and is used for reversing residual benzodiazepine-induced sedation and suspected benzodiazepine overdose.

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