NSAIDs

When tissue is injured, an enzyme called cyclooxygenase (COX) turns arachidonic acid into prostaglandins — the molecules that sensitize pain nerves, drive inflammation (swelling, redness, heat), and reset the hypothalamus to make fever. An NSAID blocks COX, so it is simultaneously an analgesic, an anti-inflammatory, and an antipyretic. That is the whole therapeutic story in one sentence. But prostaglandins are not only inflammatory signals — the same molecules quietly do housekeeping jobs all over the body, and blocking those is where the danger comes from.

The key is that COX comes in two forms. COX-1 is "always on" (constitutive) and makes the protective prostaglandins: they shield the stomach lining (mucus, bicarbonate, blood flow), keep the kidney perfused, and in platelets make thromboxane A₂, which promotes clotting. COX-2 is "switched on by injury" (inducible) and makes the prostaglandins of pain, inflammation, and fever — plus, in blood-vessel walls, prostacyclin (PGI₂), which *opposes* clotting. Most NSAIDs block both forms. So relieving pain (COX-2) comes bundled with stripping away stomach protection and renal perfusion (COX-1) and disturbing the clotting balance — the three organ systems where NSAIDs bite.

NSAIDs carry a genuine two-part FDA boxed warning, and both parts fall straight out of the mechanism. Part one — serious GI bleeding, ulceration, and perforation: knocking out COX-1 removes the prostaglandins that protect the stomach, so the mucosa thins and ulcerates. The frightening detail on the label is that these events can occur at any time, without warning symptoms, and can be fatal — elderly patients and those with prior ulcers, or on steroids or anticoagulants, are highest-risk. Part two — cardiovascular thrombotic events (MI and stroke): blocking COX-2 lowers the anti-clotting prostacyclin while platelet thromboxane (COX-1) keeps pushing toward clotting; the balance tilts prothrombotic. The risk can begin early and rises with dose and duration, which is why NSAIDs are absolutely contraindicated for pain around CABG heart surgery.

The kidney is the third target — not in the boxed warning, but clinically constant. Prostaglandins dilate the afferent arteriole that feeds the glomerulus; block them and renal blood flow falls, causing acute kidney injury, sodium and water retention (edema), hyperkalemia, higher blood pressure, and worsened heart failure. This is dangerous enough to have a nickname: the "triple whammy" — an NSAID + an ACE inhibitor/ARB + a diuretic together can collapse filtration pressure and precipitate AKI. Two special cases round it out: aspirin blocks platelet COX-1 irreversibly (a lasting antiplatelet effect, and a reason to avoid it in children with viral illness — Reye syndrome), and some patients have aspirin-exacerbated respiratory disease ("Samter’s triad": asthma + nasal polyps + NSAID sensitivity), where an NSAID triggers bronchospasm.

Because the risks are dose- and duration-dependent, the guiding rule is the lowest effective dose for the shortest necessary time — and a real reckoning with *who* is in front of you. For a high GI-risk patient (older adult, prior ulcer, on a steroid or anticoagulant), pairing the NSAID with a proton pump inhibitor for gastroprotection, or choosing a COX-2-selective agent (celecoxib, which spares the stomach) is standard — though the COX-2 selectivity that protects the gut can worsen the cardiovascular balance, so it is not a free lunch. Ketorolac deserves its own flag: it is a potent NSAID for short-term acute pain limited to ≤5 days total because GI-bleed risk climbs steeply beyond that.

A word on the popular idea that "naproxen is easier on the heart." Observational data hint at it, but the FDA did not adopt it as a labeling conclusion and the head-to-head PRECISION trial found comparable cardiovascular event rates — so treat lower-CV-risk claims cautiously rather than as fact. Finally, pregnancy: avoid NSAIDs from about 20 weeks on (fetal kidney effects → low amniotic fluid) and especially in the third trimester (premature closure of the fetal ductus arteriosus). The dependable through-line for the nurse is simple: watch the gut, the heart, and the kidney, and reassess whether the drug is still needed.