Pharmacology · USMLE Step 1

USMLE Pharmacology: Drug Classes and Mechanisms I

High-yield drug classes (first half of the alphabet by system: CNS, cardiovascular, autonomic) with mechanism of action, one card per class or key drug.

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SSRIs: What is their primary mechanism of action?
Inhibit selective reuptake of serotonin at the presynaptic terminal
SNRIs: What neurotransmitters do they block reuptake of?
Serotonin and norepinephrine
Tricyclic antidepressants: What is their mechanism?
Block reuptake of norepinephrine and serotonin, plus antimuscarinic and antihistamine effects
Monoamine oxidase inhibitors: How do they work?
Inhibit the enzyme MAO, preventing breakdown of serotonin, norepinephrine, and dopamine
Atypical antipsychotics: What is their mechanism?
Block D2 dopamine receptors and 5-HT2 serotonin receptors
Typical antipsychotics: What is their mechanism?
Block D2 dopamine receptors, primarily in the mesolimbic pathway (antipsychotic effect); also block D2 receptors in the nigrostriatal pathway, causing extrapyramidal side effects, and in the tuberoinfundibular pathway, causing hyperprolactinemia
Benzodiazepines: How do they enhance CNS depression?
Potentiate GABA-A receptor function, increasing chloride channel opening
Barbiturates: What is their mechanism?
Enhance GABA-A receptors and also directly open chloride channels, producing CNS depression
Amphetamines: How do they increase alertness?
Increase release of norepinephrine and dopamine, inhibit their reuptake
Lithium: What is its proposed mechanism in bipolar disorder?
Inhibits inositol monophosphatase, disrupting the phosphatidylinositol cycle, reducing IP3 signaling
Phenytoin (anticonvulsant): What is its mechanism?
Blocks voltage-gated sodium channels, stabilizing neuronal membranes
Opioids: How do they produce analgesia?
Bind to mu, delta, and kappa opioid receptors, decreasing neurotransmitter release and hyperpolarizing neurons
Acetaminophen: What is its mechanism of analgesia?
Inhibits cyclooxygenase (COX) in the CNS and also acts on serotonergic and endocannabinoid pathways
NSAIDs: What enzyme do they inhibit?
Cyclooxygenase (COX-1 and COX-2), decreasing prostaglandin and thromboxane synthesis
Alpha-1 agonists (e.g., phenylephrine): What is their effect?
Activate alpha-1 adrenergic receptors, causing vasoconstriction and increasing blood pressure

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