Repeated USMLE Questions- Pharmacology MCQs- 214

B- Antagonist-Antagonists work by blocking or inhibiting the action of agonists, which are drugs or endogenous substances that bind to receptors and produce a pharmacological response. By binding to receptors without activating them, antagonists prevent agonists from exerting their effects, effectively blocking or reducing the response mediated by the receptor. In contrast, agonists and partial agonists whether they are drugs or endogenous substances bind to receptors to activate them, producing a pharmacological effect.

D- Quaternary amines- Quaternary amines are a type of amine compound where the nitrogen atom is bonded to four carbon atoms. In this arrangement, the nitrogen atom carries a positive charge (quaternary nitrogen). This positive charge makes quaternary amines permanently charged. Primary amines have one alkyl or aryl group attached to the nitrogen atom. Secondary amines have two alkyl or aryl groups attached to the nitrogen atom. Tertiary amines have three alkyl or aryl groups attached to the nitrogen atom. Unlike quaternary amines, primary, secondary, and tertiary amines do not have a permanent positive charge on the nitrogen atom because they can donate a pair of electrons to form a covalent bond with a proton (H+), resulting in the formation of a temporary positive charge. However, quaternary amines have all their valence electrons used in bonds, so they cannot donate any electrons, leading to a permanent positive charge on the nitrogen atom.

A- A weak base- Aspirin is a weak acid. When the urine becomes more alkaline (basic), it promotes the ionization of weak acids like aspirin. This ionization leads to increased solubility and excretion of aspirin in the urine, reducing its toxicity.