Step 1 General Pharmacology
General Pharmacology on USMLE Step 1 covers two domains: pharmacokinetics (what the body does to the drug — absorption, distribution, metabolism, excretion) and pharmacodynamics (what the drug does to the body — receptor signaling, dose-response relationships, agonism, antagonism). Autonomic pharmacology and clinical toxicology round out the area, making it one of the broadest on the exam. If you are reviewing high-yield pharmacology concepts for Step 1, PK/PD fundamentals and toxicology antidotes are the two clusters that recur most heavily.
Questions rarely test definitions in isolation. A vignette might describe a patient on rifampin whose oral contraceptive fails, requiring you to connect CYP induction to reduced drug levels. Students consistently confuse loading dose and maintenance dose adjustments — loading dose depends on volume of distribution and does not change in renal failure, while maintenance dose depends on clearance and must be reduced. Toxicology questions often hinge on a single distinguishing feature — miosis vs mydriasis, QRS widening vs QTc prolongation, clonus vs lead-pipe rigidity — so precision matters more than breadth.
The trickiest Step 1 pharmacology material involves overlapping concepts: partial agonists acting as antagonists when a full agonist is present, or why the first treatment in pheochromocytoma must be an alpha-blocker rather than a beta-blocker. Another misconception that appears on USMLE pharmacology questions: students assume beta-blockers are safe in cocaine toxicity because of the tachycardia, but unopposed alpha-1 stimulation worsens vasospasm. These are the exact spots where half-knowledge collapses under exam pressure.
ADME and Bioavailability
Bioavailability, first-pass metabolism, and which routes bypass hepatic extraction.
- Assumes IV drugs undergo first-pass and have F < 1
- Mislocates first-pass metabolism to the stomach rather than intestine/liver
Volume of Distribution (Vd)
Predicts drug dialyzability and drives the loading dose calculation.
- Confuses high Vd with good dialyzability
- Incorrectly links lipophilicity to low Vd
Clearance and Half-Life
Steady-state timing, plateau concentration, and dose adjustments in organ failure.
- Thinks steady state has a fixed time rather than being 4–5 half-lives
- Fails to connect reduced renal clearance to prolonged half-life and drug accumulation
First-Order vs Zero-Order Elimination
Zero-order kinetics drugs — phenytoin, ethanol — and why overdose is dangerous.
- Confuses zero-order (constant amount) with first-order (constant fraction) elimination
- Misclassifies phenytoin as a first-order drug
Loading and Maintenance Dosing
Loading dose depends on Vd; maintenance dose depends on clearance — not interchangeable.
- Incorrectly reduces loading dose in renal failure when only maintenance dose requires adjustment
- Thinks loading doses are universally required rather than reserved for urgent situations with long-t1/2 drugs
Phase I vs Phase II Metabolism
Phase I oxidizes, phase II conjugates; LOT benzodiazepines survive liver disease via phase II.
- Overgeneralizes that all phase II products are inactive without understanding the excretion rationale
- Thinks LOT benzos bypass metabolism entirely rather than relying on preserved phase II conjugation
P450 Inducers and Inhibitors
Rifampin induces, azole antifungals inhibit — predicting substrate toxicity or treatment failure.
- Assumes CYP induction is immediate rather than delayed due to required new enzyme synthesis
- Ignores that CYP inhibition of a prodrug reduces efficacy rather than increasing toxicity
Urine pH and Ion Trapping
Alkalinizing urine traps weak acids like aspirin in ionized form, accelerating excretion.
- Reverses the relationship between urine pH and ion trapping for weak acids vs weak bases
- Recommends urine acidification instead of alkalinization for aspirin overdose management
Efficacy vs Potency
Emax defines ceiling effect; EC50 defines potency — a rightward shift changes only the latter.
- Equates higher potency with greater clinical effectiveness
- Interprets a rightward dose-response curve shift as reduced efficacy rather than reduced potency
Agonist Types (Full, Partial, Inverse)
Partial agonists antagonize full agonists when co-administered — buprenorphine is the key clinical example.
- Fails to recognize that a partial agonist can antagonize a full agonist when both are present
- Conflates inverse agonists with competitive antagonists
Competitive vs Non-Competitive Antagonists
Competitive antagonists shift the curve right; noncompetitive antagonists lower the ceiling.
- Confuses competitive antagonist effect on Emax vs EC50
- Confuses non-competitive antagonist binding site with competitive antagonist binding site
Therapeutic Index (TI)
Narrow-TI drugs — digoxin, warfarin, lithium — require serum monitoring because the margin is small.
- Inverts the therapeutic index formula (ED50/LD50 instead of LD50/ED50)
- Equates wide therapeutic index with absence of serious adverse effects
Receptor Signaling Families
Ion channels respond fastest; intracellular receptors (steroids) respond slowest — speed maps to location.
- Confuses fastest signal speed: attributes it to GPCRs rather than ligand-gated ion channels
- Misplaces steroid hormone receptors on the cell membrane instead of intracellularly
G-Protein Subtypes (Gs, Gi, Gq)
Gs raises cAMP, Gi lowers it, Gq triggers IP3/DAG/Ca²⁺ — cholera and pertussis toxins lock these pathways.
- Confuses Gq second messenger (IP3/DAG/Ca2+) with Gs second messenger (cAMP)
- Confuses Gi effect on adenylyl cyclase: thinks it stimulates rather than inhibits
Autonomic Anatomy and Neurotransmitters
Sympathetic postganglionic fibers release NE except to sweat glands, which are cholinergic.
- Confuses sympathetic postganglionic neurotransmitter: thinks ACh, actually NE
- Misses the cholinergic exception for sympathetic innervation of sweat glands
Cholinergic Agonists (Direct and Indirect)
Physostigmine crosses the BBB; neostigmine does not — this distinction determines central vs peripheral use.
- Confuses neostigmine with physostigmine for central anticholinergic reversal due to BBB penetrance difference
- Confuses indirect mechanism of AChE inhibitors with direct muscarinic receptor activation
Cholinergic Antagonists (Muscarinic Blockers)
Anticholinergic toxidrome — dry, hot, blind, confused, retained — is reversed by physostigmine.
- Confuses atropine (anticholinergic) with physostigmine (antidote) for anticholinergic toxidrome
- Assumes ganglionic and NMJ nicotinic receptors are identical and blocked by the same agents
Organophosphate Poisoning and Pralidoxime
Atropine blocks muscarinic signs; pralidoxime regenerates AChE at the NMJ before aging locks it.
- Thinks atropine alone treats organophosphate poisoning, missing the need for pralidoxime at the NMJ
- Misses the concept of organophosphate aging that renders pralidoxime ineffective if delayed
Adrenergic Agonists (Direct)
Norepinephrine causes reflex bradycardia via baroreceptors despite its beta-1 activity.
- Predicts tachycardia with NE due to beta-1 stimulation, missing the dominant baroreceptor reflex
- Predicts DBP increase with isoproterenol, missing beta-2 vasodilation that lowers DBP
Indirect Sympathomimetics
Beta-blockers are contraindicated in cocaine chest pain because unopposed alpha-1 worsens vasospasm.
- Confuses cocaine's reuptake-blocking mechanism with amphetamine's active NE-releasing mechanism
- Recommends beta-blockers for cocaine chest pain, missing the risk of unopposed alpha-1 coronary vasospasm
Adrenergic Antagonists (α and β)
Alpha-blockade before beta-blockade in pheochromocytoma prevents hypertensive crisis from unopposed alpha receptors.
- Confuses the order of adrenergic blockade in pheochromocytoma, giving β-blocker first
- Underestimates the dual danger of non-selective β-blockers in diabetics by missing the glycogenolysis blockade
Acetaminophen Toxicity and NAC
NAPQI from CYP2E1 depletes glutathione — NAC replenishes it, and timing relative to ingestion is critical.
- Attributes hepatotoxicity to acetaminophen directly rather than to its CYP2E1-generated metabolite NAPQI
- Misidentifies NAC's mechanism as direct NAPQI neutralization rather than glutathione replenishment
Salicylate (Aspirin) Toxicity
Early respiratory alkalosis precedes metabolic acidosis; bicarbonate drives urinary ion trapping, not just pH correction.
- Misses the early respiratory alkalosis phase of salicylate toxicity, expecting only metabolic acidosis
- Attributes bicarbonate use in salicylate overdose solely to acidosis correction, missing urinary ion trapping as the primary goal
Sedative and Opioid Reversal
Naloxone duration is shorter than most opioids; flumazenil precipitates seizures in dependent patients.
- Overlooks flumazenil's seizure-precipitating risk in dependent patients or TCA co-ingestion
- Assumes one naloxone dose is sufficient for opioid reversal, ignoring its shorter duration relative to most opioids
Anticoagulant Reversal
Andexanet alfa reverses factor Xa inhibitors; idarucizumab reverses dabigatran — vitamin K does neither.
- Applies warfarin reversal strategy (vitamin K/FFP) to DOAC overdose, ignoring DOAC-specific antidotes
- Assumes protamine sulfate provides complete reversal of LMWH as it does for unfractionated heparin
Digoxin Toxicity
Hypokalemia potentiates digoxin toxicity; IV calcium is contraindicated; xanthopsia is the classic visual finding.
- Misses that hypokalemia (e.g., from diuretics) dramatically increases digoxin toxicity by enhancing its binding to Na+/K+-ATPase
- Misidentifies digoxin's visual toxicity as nonspecific blurring rather than the classic yellow-green xanthopsia
Toxic Alcohols and Gas Poisoning
Methanol targets the optic nerve; ethylene glycol targets the kidneys; CO saturates hemoglobin invisibly on pulse ox.
- Confuses methanol's end-organ target (optic nerve/blindness) with ethylene glycol's target (renal failure)
- Trusts pulse oximetry to rule out CO poisoning, unaware it cannot distinguish carboxyhemoglobin from oxyhemoglobin
TCA Overdose
QRS widening — not QTc — signals cardiac danger; sodium bicarbonate works via Na+ loading, not pH.
- Attributes bicarbonate's benefit in TCA overdose to acidosis correction rather than Na+ loading and Na+ channel unblocking
- Focuses on QTc prolongation as the key ECG risk marker in TCA overdose, missing that QRS widening is the more critical finding
β-Blocker and Calcium Channel Blocker Overdose
Glucagon bypasses the beta receptor to raise cAMP; hyperglycemia distinguishes CCB overdose from beta-blocker overdose.
- Misattributes glucagon's benefit in β-blocker overdose to β-receptor activation rather than receptor-independent cAMP elevation
- Fails to use glucose level to distinguish CCB overdose (hyperglycemia) from β-blocker overdose (hypoglycemia)
Heavy Metal Poisoning and Chelators
Succimer treats mild lead toxicity orally; dimercaprol covers arsenic and mercury; zinc maintains Wilson disease.
- Applies a single chelation protocol to all lead toxicity levels, missing the level-dependent choice between oral succimer and parenteral dimercaprol/EDTA
- Misses that dimercaprol (BAL) is the shared chelator for both arsenic and mercury poisoning
Methemoglobinemia
Fe³⁺ cannot carry oxygen; methylene blue activates NADPH reductase — useless in G6PD deficiency.
- Confuses ferric (Fe3+) state of methemoglobin with the normal ferrous (Fe2+) state
- Misunderstands methylene blue as a direct chemical antidote rather than a cofactor-dependent enzyme activator
Serotonin Syndrome, NMS, Malignant Hyperthermia
Clonus and hyperreflexia point to serotonin syndrome; lead-pipe rigidity and low dopamine point to NMS.
- Confuses the neuromuscular findings of serotonin syndrome (clonus/hyperreflexia) with NMS (lead-pipe rigidity)
- Misattributes NMS to dopamine excess rather than dopamine receptor blockade by antipsychotics
Antidote Quick Table (High-Yield)
High-yield pairings tested as distractors: NAC for APAP, Fab for digoxin, fomepizole for toxic alcohols.
- Misunderstands NAC as a direct NAPQI neutralizer rather than a glutathione precursor
- Overlooks pralidoxime as a necessary co-treatment with atropine in organophosphate toxicity
Teratogens
Lithium causes Ebstein anomaly; valproate causes neural tube defects; tetracyclines stain developing teeth.
- Confuses lithium's teratogenic effect (Ebstein anomaly) with valproate's neural tube defect association
- Overestimates folate's protective effect against valproate teratogenicity
Beers Criteria (Potentially Inappropriate Medications in Older Adults)
Anticholinergics and long-acting benzodiazepines top the avoid list in older adults — Beers guides, not prohibits.
- Treats Beers Criteria as an absolute contraindication list rather than a clinical guidance tool
- Misattributes the main risk of NSAIDs in older adults to hepatotoxicity rather than GI/renal/cardiovascular harm
Seafood Toxins (Scombroid, Ciguatera, Tetrodotoxin, Saxitoxin)
Scombroid is histamine poisoning from spoiled fish; ciguatera reverses temperature sensation; tetrodotoxin blocks Na+ channels.
- Confuses scombroid poisoning (histamine toxicity from spoiled fish) with a true fish allergy
- Confuses the ion channel target of tetrodotoxin/saxitoxin (Na+ channel blockade) with potassium channel blockade
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