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Abnormal Foundations of Pharmacology

CPR APPLICATIONS FOUNDATION · CHAPTER 5 · ABNORMAL

Abnormal Foundations of Pharmacology

Organize the chapter before drilling into individual CPR concepts.

Supplemental foundation map: this page orients the detailed CPR Applications for Chapter 5. It is not part of the canonical CPR object inventory.

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5.9 · SOURCE CPR FOUNDATION

Concept

Abnormal pharmacology begins when patient factors change how the body handles a drug or how the drug affects the body. Pharmacokinetics explains drug concentration through absorption, distribution, metabolism, and elimination. Pharmacodynamics explains drug effect at the receptor or response pathway.

Pattern

Step 1 usually follows the sequence: patient change → drug level or drug response change → toxicity or failure. Pharmacokinetic questions focus on concentration changes despite the same dose. Pharmacodynamic questions focus on altered response despite similar drug concentration.

Rule

  1. If concentration changes, think pharmacokinetics: absorption, distribution, metabolism, elimination, protein binding, and drug interactions determine drug level.
  2. If the effect changes at the same concentration, think pharmacodynamics: receptor number, receptor sensitivity, antagonism, and downstream signaling determine response.
  3. Classify the clinical problem as too much, too little, or ineffective: toxicity, treatment failure, and receptor-level resistance each point to different mechanisms.

Applications

  • Clarithromycin plus simvastatin → CYP3A4 inhibition increases simvastatin exposure and myopathy risk; not all macrolides or statins share this interaction
  • Rifampin plus oral contraceptive → reduced efficacy
  • Renal failure plus lithium → accumulation toxicity
  • Naloxone plus morphine → competitive antagonism
  • High-affinity partial μ-opioid agonist buprenorphine can displace a full agonist and precipitate withdrawal when initiated too early in an opioid-dependent patient; effects depend on the clinical context

CPR APPLICATIONS · ACTIVE REASONING

Separate pharmacokinetics from pharmacodynamics

Make a prediction before checking the explanation. Every worked answer is also available below without scripts. No learner answers are transmitted or retained.

Decision 1. A patient with severe acute kidney injury continues an unchanged lithium regimen. Which mechanism most plausibly raises toxicity risk?
Reveal worked answer and changed-variable prompt

Best answer: Reduced renal lithium clearance increases exposure. Correct. Lithium is eliminated primarily by the kidney; impaired renal function can increase concentration and toxicity risk.

Transfer: If the concentration remains unchanged but the effect increases, why is the mechanism more consistent with pharmacodynamics?

Decision 2. A patient stable on simvastatin starts clarithromycin and later develops muscle symptoms. Which change best explains the interaction?
Reveal worked answer and changed-variable prompt

Best answer: CYP3A4 inhibition increases simvastatin exposure. Correct. Clarithromycin inhibits CYP3A4 and can markedly increase simvastatin exposure and myopathy risk.

Transfer: Would azithromycin with pravastatin imply an identical CYP3A4 interaction? No.

Decision 3. Naloxone reverses opioid receptor activation after a full agonist was given. What accounts for the reduced receptor signaling?
Reveal worked answer and changed-variable prompt

Best answer: Competitive μ-opioid receptor antagonism. Correct. Naloxone binds opioid receptors without producing the full agonist effect, displacing agonist activity.

Transfer: Why does naloxone action sometimes end before that of the opioid? Drug-specific duration and re-sedation risk.

Change the mechanism

Reference consequences without scripts
  • Change: renal lithium clearance falls: Expected lithium concentration rises unless therapy is adjusted and monitored.
  • Change: CYP3A4 inhibition with simvastatin: Reduced metabolism raises active drug exposure and risk of toxicity.
  • Change: competitive antagonist at μ receptor: Signaling falls at the receptor even without first lowering the circulating agonist concentration.

Explain it back: State the causal chain in your own words and identify which observation would falsify your first prediction.

These are educational, unscored self-checks rather than validated assessments or clinical treatment advice.

How to use this foundation map

  1. Identify the organizing mechanism.
  2. Recognize the pattern.
  3. Restate the rule without looking.
  4. Test transfer with the applications and question practice.

Pair CPR with the 5P Approach™ when solving cases and questions.

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