Pharmacology Case Study: Valproic Acid
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Questions and Answers

What is the primary focus of pharmacokinetics?

  • The study of antidotes in poisoning treatment
  • The study of drug abuse and addiction
  • The study of ADME at therapeutic doses (correct)
  • The study of ADME at toxic doses
  • What can alter the rate and extent of absorption?

  • Multiple factors, including formulation, bioavailability, and co-ingestants (correct)
  • Only the formulation of the product
  • Only the dose of the drug
  • Only the route of administration
  • What is the primary difference between pharmacokinetics and toxicokinetics?

  • The route of administration
  • The type of drug being studied
  • The dose of the drug being studied (correct)
  • The duration of treatment
  • What can slow or decrease GI absorption?

    <p>Multiple factors, including anticholinergic agents, opioids, and large ingestions (D)</p> Signup and view all the answers

    What can be used to predict the onset of efficacy/toxicity?

    <p>Pharmaco/toxicokinetics (A)</p> Signup and view all the answers

    What is the result of concretions/pharmacobezoar?

    <p>Aggregation into a mass (B)</p> Signup and view all the answers

    How does the formulation of a product affect its absorption?

    <p>It affects both the rate and extent of absorption (A)</p> Signup and view all the answers

    What is the result of opening, crushing, or breaking sustained release products?

    <p>Faster rate of absorption (C)</p> Signup and view all the answers

    What is the focus of toxicokinetics?

    <p>The study of ADME at doses above the therapeutic dose (D)</p> Signup and view all the answers

    What is the result of slowed absorption?

    <p>Increased toxicity (A)</p> Signup and view all the answers

    Study Notes

    Protein Binding

    • Binding capacity becomes saturated, leading to an increase in the free/bound ratio
    • An increase in free concentration can result in effects
    • Example: 32-year-old with valproic acid overdose, medical student looks up information, and poison center specialist suggests dialysis despite manufacturer's info saying it's not dialyzable

    Phenytoin

    • 17-year-old with phenytoin toxicity, ataxic and bumping into things
    • Level is 26 mcg/ml, higher than usual due to significant weight loss (anorexia) and low albumin level (2.5 mg/dl)
    • Free phenytoin level is very high, corrected level of 43 mcg/ml compared to 28 mcg/ml with normal albumin level

    Metabolism

    • Liver is the major organ involved in metabolism
    • Oxidation, reduction, hydrolysis, and conjugation occur through the P-450 enzyme system
    • Metabolism can result in:
      • Active medication to inactive metabolites
      • Active drug to active metabolites + inactive metabolites
      • Inactive medication to active medication
    • Examples of active drug to active/toxic metabolites:
      • Citalopram/Escitalopram, where desmethylcitalopram metabolite is responsible for qt prolongation
      • Methanol and Ethylene glycol, where metabolism can be blocked using Fomepizole (4mp) or Ethanol

    Elimination

    • Irreversible loss of substance from the site of measurement
    • Total clearance is the sum of renal clearance, metabolic clearance, and other clearance mechanisms
    • Renal elimination involves glomerular filtration, secretion, and reabsorption
    • Example: ASA (weak acid), where using NaBicarb can increase elimination by ion trapping and raising plasma and urine pH

    Half-life

    • Time for the medication concentration to decrease by ½
    • Half-life is substance-specific, patient-specific, and influenced by organ function, age, disease states, and other medications
    • Half-life relates to the duration of toxicity

    Pharmacodynamics vs Toxicodynamics

    • Insulin, BB, water, opioid, benzodiazepines, and almost every medication can have different effects at toxic levels

    Idiosyncratic Side Effects

    • Rare after an overdose
    • Risk of idiosyncratic effects is not more common after an overdose compared to a therapeutic dose

    Antidotes

    • Examples of antidotes carried by EMS/Paramedics:
      • Naloxone
      • Glucose
      • Oxygen
      • Atropine
      • Physostigmine
      • Pralidoxime (2-Pam)
    • Examples of antidotes carried by hospitals:
      • Cyanide antidote kits
      • Snake antivenin (some hospitals)
      • Succimer
      • Calcium Disodium Versonate
      • Antibiotics (for anthrax)
    • Specialized resources:
      • Snake antivenin (some hospitals)
      • HBO
      • Botulism immune globulin
      • Strategic National Stockpile

    Pharmacokinetics vs Toxicokinetics

    • Pharmacokinetics: the study of ADME at therapeutic doses
    • Toxicokinetics: the study of ADME at doses above the therapeutic dose, which can result in altered absorption, distribution, metabolism, and elimination rates
    • Therapeutic dose vs excessive dose: absorption, distribution, metabolism, and elimination can be altered at excessive doses

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    Related Documents

    Description

    A case study on valproic acid poisoning, involving a 32-year-old patient with a high serum level. The scenario requires knowledge of protein binding and dialysis.

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