Pharmacology and Prescribing
Pharmacology and Prescribing tests safe medication decision-making under emergency conditions: dose selection, adjustment for organ function and weight, interactions, reversal, and stewardship of high-risk classes. Items often hinge on a single dosing or interaction detail.
Principles that drive most items
- Weight-based dosing for children and for select adult drugs; know ideal body weight and adjusted body weight applications (for example, aminoglycoside dosing in obesity).
- Estimate creatinine clearance with Cockcroft-Gault rather than relying on a serum creatinine that looks normal in a frail older adult.
- Renal adjustments matter for enoxaparin (avoid or adjust when CrCl <30 mL/min), most antimicrobials, and gabapentin; NSAIDs are generally avoided in chronic kidney disease.
- High-alert medications - insulin, heparin, opioids, concentrated electrolytes - require independent double-checks and standardized concentrations.
- QT prolongation is additive: ondansetron, droperidol, macrolides, fluoroquinolones, and methadone stack. Check potassium and magnesium.
- Apply Beers criteria thinking to older adults: avoid diphenhydramine, benzodiazepines, and long-acting sulfonylureas when safer options exist.
Reversal and antidotes
- Naloxone: titrate to adequate respiration, not to full arousal.
- Warfarin with major bleeding: intravenous vitamin K plus four-factor prothrombin complex concentrate; plasma is slower and second-line.
- Dabigatran: idarucizumab. Factor Xa inhibitors: andexanet alfa or prothrombin complex concentrate per protocol.
- Acetaminophen: N-acetylcysteine, most effective early. Benzodiazepine overdose: supportive care; flumazenil risks seizure.
Worked example
A 78-year-old on warfarin for atrial fibrillation presents with hematemesis, INR 8.2, and BP 92/58. Reasoning: this is life-threatening bleeding, so hold warfarin and give intravenous vitamin K 5–10 mg plus four-factor prothrombin complex concentrate for immediate factor replacement; transfuse for hemodynamics and activate the GI bleed pathway. Waiting for plasma thawing wastes time.
Traps that cost marks
- Assuming a creatinine of 1.0 mg/dL means normal renal function in a 90-year-old.
- Missing additive QT prolongation across the medication list.
- Over-documenting "allergy" to a drug that caused only a predictable side effect, forcing inferior alternatives.
- Prescribing without checking the prescription monitoring program in a patient on chronic opioids.