Page 279 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

Pharmacology ` PHARMACOLOGY—PHARMACOKINETICS ANd PHARMACOdYNAMICS Pharmacology ` PHARMACOLOGY—PHARMACOKINETICS ANd PHARMACOdYNAMICS SEcTIoN II 235

Types of drug interactions
TERM dEFINITION EXAMPLE
Additive Effect of substances A and B together is equal to Aspirin and acetaminophen
the sum of their individual effects “2 + 2 = 4”
Permissive Presence of substance A is required for the full Cortisol on catecholamine responsiveness
effects of substance B
Synergistic Effect of substances A and B together is greater Clopidogrel with aspirin
than the sum of their individual effects “2 + 2 > 4”

Potentiation Similar to synergism, but drug B with no Carbidopa only blocks enzyme to prevent
therapeutic action enhances the therapeutic peripheral conversion of levodopa
action of drug A “2 + 0 > 2”
Antagonistic Effect of substances A and B together is less Ethanol antidote for methanol toxicity
than the sum of their individual effects “2 + 2 < 4”
Tachyphylactic Acute decrease in response to a drug after Nitrates, niacin, phenylephrine, LSD, MDMA
initial/repeated administration

FAS1_2019_05-Pharmacology.indd 235 11/7/19 4:08 PM