Which enzyme is best described as constitutive, protecting the stomach lining, supporting renal blood flow, and enabling normal platelet function?
Choose an answer, then check it.
Clinical Pharmacology · Pain Management
NSAIDs
On this page 6 sections
In 30 seconds
NSAIDs (nonsteroidal anti-inflammatory drugs) relieve pain by blocking cyclooxygenase (COX) enzymes, which stops production of prostaglandins that sensitize pain receptors and drive fever and inflammation. They work well for mild-to-moderate pain, especially pain with an inflammatory or musculoskeletal component, but they have a ceiling effect and a predictable set of adverse effects tied directly to the same enzyme they block. Understanding COX-1 versus COX-2 explains almost everything about why these drugs help and why they hurt.
The college version
The Cyclooxygenase Pathway
Cell membranes release arachidonic acid, which cyclooxygenase enzymes convert into prostaglandins and thromboxane. Two COX isoforms matter clinically. COX-1 is constitutive, meaning it is expressed continuously in most tissues to perform housekeeping functions: it maintains the protective mucus and bicarbonate layer of the gastric lining, supports renal blood flow (especially when the kidney is under stress), and enables platelets to produce thromboxane A2 for clotting. COX-2 is largely inducible, meaning its expression rises sharply at sites of tissue injury and inflammation, where it generates the prostaglandins responsible for pain sensitization, fever, vasodilation, and swelling. Traditional NSAIDs inhibit both COX-1 and COX-2 nonselectively, which is why they relieve pain and fever but also disrupt gastric protection, renal autoregulation, and platelet function. Celecoxib inhibits COX-2 preferentially, sparing much of the COX-1-mediated gastric and platelet activity, though it does not eliminate renal or cardiovascular risk.
Therapeutic Effects
Because prostaglandins sensitize peripheral nociceptors to painful stimuli, blocking their synthesis produces analgesia, most useful for musculoskeletal pain, dysmenorrhea, dental pain, and mild-to-moderate postoperative pain. The same mechanism resets the hypothalamic set point elevated by pyrogens, producing an antipyretic effect, and reduces vasodilation, edema, and leukocyte activity at inflamed tissue, producing an anti-inflammatory effect. NSAIDs also produce an antiplatelet effect by reducing thromboxane A2, which discourages platelet aggregation.
Ceiling Effect and Combination Strategy
NSAID analgesia has a ceiling: once COX enzymes are maximally inhibited, increasing the amount further adds adverse-effect risk without added pain relief, unlike opioids, which have no defined analgesic ceiling. This is the pharmacologic rationale for multimodal analgesia — pairing an NSAID with acetaminophen (which acts through a different, largely central mechanism) or with an opioid to relieve pain through separate pathways simultaneously. This can improve pain control while lowering the opioid amount needed.
Major Agents and Subgroups
Ibuprofen and naproxen are commonly used nonselective NSAIDs for general aches, musculoskeletal pain, and dysmenorrhea; naproxen has a longer duration of action. Ketorolac is a potent nonselective NSAID reserved for short-term management of moderate-to-severe acute pain, often as a nonopioid option perioperatively; its use is intentionally limited to a brief course because prolonged use sharply raises gastrointestinal, renal, and bleeding risk — its benefit is front-loaded while its risk accumulates with continued exposure. Indomethacin is a potent nonselective NSAID with a notably higher incidence of central nervous system and gastrointestinal adverse effects. Diclofenac is available in oral and topical forms, the latter allowing localized action with reduced systemic exposure. Meloxicam is a nonselective NSAID that shows some preferential COX-2 activity at lower ends of its dosing range, giving it a somewhat more favorable gastrointestinal profile than older agents, though it is not COX-2 selective in the way celecoxib is. Celecoxib, a COX-2 selective inhibitor, reduces gastric and antiplatelet effects relative to nonselective NSAIDs but does not eliminate renal risk and carries its own cardiovascular thrombotic concern.
Aspirin deserves separate mention because its mechanism differs from every other NSAID. Aspirin irreversibly acetylates COX, permanently disabling the enzyme for the lifespan of that platelet (platelets cannot synthesize new enzyme because they lack a nucleus). This effect lasts for the platelet's full lifespan and is why low-dose aspirin is used for cardiovascular protection, while other NSAIDs produce only reversible, dose-limited platelet inhibition.
Adverse Effects Organized by Mechanism
Gastrointestinal: loss of COX-1-dependent mucosal protection allows acid injury, ulceration, and bleeding, which can occur even without preceding pain symptoms. Renal: renal prostaglandins maintain glomerular perfusion when blood flow is compromised; NSAIDs blunt this compensatory vasodilation, raising acute kidney injury risk during hypovolemia, dehydration, or heart failure, and this risk compounds when combined with an ACE inhibitor or ARB plus a diuretic — sometimes called the "triple whammy," since each drug independently reduces renal perfusion or filtration. Fluid and blood pressure: prostaglandin inhibition promotes sodium and water retention, which can elevate blood pressure and precipitate or worsen fluid overload, an important concern in heart failure and hypertension. Cardiovascular: nonselective and COX-2 selective NSAIDs alike carry a thrombotic risk (myocardial infarction and stroke), thought to relate to an imbalance between prostacyclin and thromboxane effects on vascular tone and platelet activity; this risk is a class concern, not limited to celecoxib. Respiratory: in aspirin-exacerbated respiratory disease, blocking COX shunts arachidonic acid toward the lipoxygenase pathway, increasing leukotriene production and provoking bronchospasm in susceptible patients, particularly those with asthma and nasal polyps. Pediatric: aspirin use during a viral illness in children is linked to Reye syndrome, a rare but serious hepatic and encephalopathic condition, which is why aspirin is avoided in children and adolescents with viral infections.
Nursing Considerations
Administer with food or milk to reduce gastric irritation. Monitor renal function, particularly in older adults, those who are volume-depleted, or those on concurrent ACE inhibitor/ARB and diuretic therapy. Observe for signs of gastrointestinal bleeding (dark stools, hematemesis) and apply bleeding precautions, especially alongside anticoagulants or antiplatelet agents. Monitor blood pressure and for signs of fluid retention. Ask about asthma and nasal polyp history before administering, and never give aspirin to a child or adolescent with a suspected viral illness.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Imagine your body has two teams of workers, both named COX. Team COX-1 does everyday maintenance jobs all the time — it patches the stomach lining like a repair crew, keeps blood flowing steadily to the kidneys, and helps blood cells stick together to stop bleeding. Team COX-2 only shows up when there's an injury, like firefighters rushing to a fire — it's the one that makes the area hurt, swell, and feel hot so you notice and protect it.
NSAID medicines tell both teams to stop working. That's great for the fire — less pain, less swelling, lower fever. But most NSAIDs can't tell the two teams apart, so the maintenance crew stops too, and now the stomach lining isn't as protected, the kidneys don't get as much steady blood flow, and blood doesn't clot as easily. There's also a limit to how much good one dose can do — take more and you just get more side effects, not more pain relief, so doctors often add a different kind of pain reliever instead of just piling on more NSAID.
Aspirin is the odd one out: it doesn't just tell COX to pause, it breaks the switch permanently in blood cells called platelets, and those platelets can never fix that switch because they don't have the tools to build a new one. That's why a little aspirin can protect the heart for a long time.
Check yourself
2 review questions from the chapter. Try each one, then open the answer.
A nurse is caring for a postoperative patient receiving ketorolac for acute pain. What key principle should guide how long this therapy continues, and why?
Show answer
Short-term use only, because prolonged exposure sharply raises bleeding, GI, and renal risk.
Ketorolac is a strong nonselective NSAID meant to bridge acute pain for a brief period; the longer it's continued, the more its gastrointestinal, renal, and bleeding risks accumulate, so it is intentionally not used as a long-term pain medication.
A patient with asthma and nasal polyps is prescribed an NSAID for pain and develops wheezing shortly after taking it. Explain the mechanism connecting NSAID use to this reaction.
Show answer
Blocking COX shunts arachidonic acid toward the lipoxygenase pathway, increasing leukotrienes that trigger bronchospasm.
In aspirin-exacerbated respiratory disease, when COX is blocked, the raw material that would have made prostaglandins gets rerouted into making more leukotrienes instead, and leukotrienes constrict the airways, producing wheezing in susceptible patients.
Quick check
3 questions here. Answers stay hidden until you check.
A patient is taking an ACE inhibitor and a diuretic and is then started on an NSAID. What is the primary concern this combination raises?
Choose an answer, then check it.
Why does aspirin's effect on platelets last far longer than that of other NSAIDs like ibuprofen?
Choose an answer, then check it.
Study tools & related lessonsRelated
Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.