A patient who takes aspirin for arthritis pain asks the nurse why it also causes gastrointestinal upset. Which of these explanations is most accurate?

Choice A rationale Aspirin, or acetylsalicylic acid, causes gastrointestinal (GI) irritation not primarily by increasing GI secretions, but by its direct irritating effect on the gastric mucosa and, more significantly, by inhibiting protective prostaglandin synthesis. Choice B rationale While hypersensitivity reactions (allergic responses) to aspirin can occur, the common GI upset experienced by many users is a pharmacologic side effect related to its mechanism of action on prostaglandin synthesis, not an allergic reaction. Choice C rationale Aspirin is a non-steroidal anti-inflammatory drug (NSAID) that non-selectively inhibits the cyclooxygenase (COX) enzymes. Inhibition of COX-1 impairs the synthesis of protective prostaglandins in the stomach, leading to reduced mucus secretion and increased acid production, causing irritation and potential ulceration. Choice D rationale Aspirin is a weak acid, and its non-ionized form is readily absorbed across the gastric mucosa, which contributes to direct local irritation; however, the major mechanism of sustained GI damage is the systemic inhibition of protective prostaglandins via COX-1.