Take the Free Diagnostic

Abnormal Foundations of Toxicology & Pharmacology Safety

CPR APPLICATIONS FOUNDATION · CHAPTER 22 · ABNORMAL

Abnormal Foundations of Toxicology & Pharmacology Safety

Organize the chapter before drilling into individual CPR concepts.

Supplemental foundation map: this page orients the detailed CPR Applications for Chapter 22. It is not part of the canonical CPR object inventory.

Browse the Foundations Library

Move through Chapter 22

Normal Foundations

Open normal foundations →

Abnormal Foundations · You are here

Open abnormal foundations →

Treatment Foundations

Open treatment foundations →

22.16 · SOURCE CPR FOUNDATION

Concept

Drug toxicity is predictable when adverse effects are treated as organ-failure patterns. Drugs can injure marrow, liver, kidney, heart rhythm, CNS, fetus, immune system, or metabolism. The same medication can be safe in one patient and dangerous in another because physiology changes risk.

Pattern

Step 1 gives a new symptom after a new medication, a drug interaction, pregnancy, CKD, liver disease, older age, baseline electrolyte abnormality, or pharmacogenomic vulnerability. The key is connecting the drug’s target and metabolism to the patient’s vulnerable organ system.

Rule

  1. New symptoms after drug initiation warrant an adverse-effect assessment, but temporality alone does not prove causality; examine alternative diagnoses, interactions, and exposure.
  2. Map the adverse effect to the organ system. Marrow, liver, kidney, rhythm, CNS, fetus, and immune system are common.
  3. Patient context changes safety. Pregnancy, CKD, liver disease, age, interactions, and genetics modify risk.

Applications

  • Jaundice after TB therapy → hepatotoxicity concern
  • Rising creatinine after NSAID in CKD → renal perfusion toxicity
  • Syncope after macrolide plus azole → QT stacking
  • Pancytopenia after chemotherapy → marrow suppression
  • Confusion after diphenhydramine in older adult → anticholinergic delirium
  • Valproate exposure in pregnancy → increased risk of neural tube defects and other fetal harms; medication changes require coordinated maternal-fetal and neurologic review
  • Tip: Pharmacology stems often ask who is vulnerable, not just what the drug does

CPR APPLICATIONS · ACTIVE REASONING

Separate toxicity from predisposition and coincidence

Predict the mechanism and consequence before checking. Worked explanations remain accessible without scripts. Responses are not stored or transmitted.

Decision 1: A patient stable on lithium develops dehydration and acute kidney injury, then tremor and confusion. Which mechanism makes lithium toxicity more plausible?

Reveal worked reasoning and transfer

Best answer: Reduced renal clearance causes lithium accumulation and neurotoxicity risk.. Lithium is predominantly renally eliminated, so loss of kidney function can raise exposure.

Change one variable: How would the causal hypothesis change if renal function and lithium concentration were unchanged?

Decision 2: A patient with hypokalemia develops syncope after adding a QT-prolonging medication to another QT-prolonging regimen. Which mechanism is concerning?

Reveal worked reasoning and transfer

Best answer: Drug-associated repolarization delay with risk of torsades de pointes.. Combining QT-prolonging exposures and low potassium can increase the risk of polymorphic ventricular tachycardia.

Change one variable: How would correction of potassium and stopping a culpable agent alter risk?

Decision 3: An older patient develops agitation, dry flushed skin, dilated pupils, and urinary retention after diphenhydramine. Which toxidrome fits best?

Reveal worked reasoning and transfer

Best answer: Antimuscarinic toxicity.. Diphenhydramine can produce central and peripheral anticholinergic effects, including delirium, dry skin, mydriasis, and urinary retention.

Change one variable: What if the patient instead had copious secretions, sweating and muscle fasciculations?

Change the mechanism

See all mechanism comparisons without scripts
  • Lithium with acute renal impairment: Impaired elimination increases exposure risk; correlate symptoms and measured levels.
  • QT-prolonging drugs plus low potassium: Additive repolarization vulnerability increases arrhythmia concern.
  • Diphenhydramine with delirium and dry skin: Antimuscarinic effects explain the characteristic peripheral and central syndrome.

Explain it back: For one question, explain why your choice is better than the strongest alternative, then identify the clinical finding that would change the conclusion.

Unscored educational exercises. Not independent clinical recommendations, validated assessments, or a substitute for local policy and expert evaluation.

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 applications and question practice.

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

Back to Chapter 22 in the Foundations Library · USMLE Step 1 resources