Source / episode info

• **Episode:**606
• **Title:**DIP Ep 606: Drug Interactions For The USMLEs (Step 1-3)
• **Published:**2025-05-26
• Source:Episode page

One-liner

This episode provides a comprehensive review of high-yield drug interactions, covering anticoagulation (Warfarin), anti-hypertensives (NSAIDs/ACEi/ARBs), antibiotics, anticonvulsants, and metabolic drugs, emphasizing the underlying mechanisms of enzyme inhibition/induction and physiological compensation.

High-yield summary

• Anticoagulation: Warfarin is highly susceptible to drug interactions via CYP enzymes (CYP3A4, CYP2C9, CYP1A2) and displacement from albumin; antibiotics (Macrolides, TMP/SMX) are major culprits.
• Renal Toxicity: Diuretics (thiazides, loop diuretics) can cause volume depletion, leading to compensatory increased proximal tubular reabsorption of sodium and lithium, increasing the risk of lithium toxicity.
• Serotonin Syndrome: This is a critical diagnosis resulting from combining multiple serotonergic agents (e.g., SSRIs + MAOIs/Triptans/St. John's Wort), requiring immediate management.
• Antihypertensive Synergy: Combining NSAIDs with ACE inhibitors or ARBs significantly increases the risk of acute kidney injury (AKI) due to opposing effects on afferent and efferent arteriolar tone, respectively.
• Drug Metabolism: Understanding CYP enzyme induction (e.g., Rifampin inducing CYP3A4) or inhibition (e.g., Azoles inhibiting CYP2C9) is key to predicting drug efficacy failure or toxicity.

Learning objectives

• Identify drug interactions involving Vitamin K antagonists (Warfarin).
• Differentiate the mechanisms leading to acute kidney injury when combining NSAIDs with RAAS inhibitors (ACEi/ARBs).
• Recognize the clinical triad and underlying mechanism of Serotonin Syndrome.
• Predict electrolyte abnormalities resulting from diuretic use, particularly concerning lithium reabsorption.
• Understand how CYP enzyme induction or inhibition affects the pharmacokinetics of commonly prescribed medications.

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