Chapter 41  ·  Module 2
NSAID Toxicity, Drug Interactions & Special Populations
Gastrointestinal, cardiovascular, renal, and population-specific risks at a glance
Abbreviations: NSAID = nonsteroidal anti-inflammatory drug  ·  COX = cyclooxygenase  ·  PGI2 = prostacyclin  ·  TXA2 = thromboxane A2  ·  PPI = proton pump inhibitor  ·  AERD = aspirin-exacerbated respiratory disease  ·  eGFR = estimated glomerular filtration rate  ·  ACE = angiotensin-converting enzyme  ·  ARB = angiotensin receptor blocker  ·  SSRI = selective serotonin reuptake inhibitor  ·  CKD = chronic kidney disease
Gastrointestinal Toxicity
High GI Risk — Any One Warrants Protection
Risk Factors
  • Prior peptic ulcer or GI bleed (strongest)
  • Age above 65
  • Concurrent anticoagulant
  • Concurrent corticosteroid
  • High NSAID dose
  • Two NSAIDs simultaneously (incl. low-dose aspirin)
  • Helicobacter pylori infection
Protective Strategies
Prevention
  • Celecoxib — less mucosal injury (benefit lost with aspirin)
  • PPI co-therapy — preferred, ~75% risk reduction
  • Misoprostol — effective but poorly tolerated (diarrhea)
  • Highest risk: celecoxib + PPI combined
  • Eradicate H. pylori before long-term NSAID use
  • Lowest effective dose, shortest duration
Key mechanism: NSAID gastropathy is systemic — prostaglandin suppression in the blood, not local drug contact. Enteric coating and parenteral routes do NOT protect the gastric mucosa.
Cardiovascular Risk — PGI2 / TXA2 Imbalance
Endothelium (COX-2)
PGI2
Anti-platelet • Vasodilation
⇋
Platelets (COX-1)
TXA2
Pro-platelet • Vasoconstriction
Selective COX-2 inhibition: suppresses endothelial PGI2 while TXA2 remains intact → prothrombotic, vasoconstrictive → elevated MI and stroke risk
CV risk hierarchy: selective COX-2 inhibitors > high-dose diclofenac/ibuprofen > naproxen (preferred in CV-risk patients)
Renal Toxicity — Class-Wide
Safe Baseline
Euvolemic Healthy Patient
  • Renal prostaglandins play minor role
  • NSAIDs cause trivial GFR reduction
  • Clinically insignificant at standard doses
High-Risk States — Avoid NSAIDs
Prostaglandin-Dependent Perfusion
  • Heart failure
  • Cirrhosis with ascites
  • Volume depletion (any cause)
  • CKD (eGFR <30: contraindicated)
  • Nephrotic syndrome
Triple Whammy — Avoid This Combination

NSAID + ACE inhibitor or ARB + Diuretic → additive reduction of GFR from three directions → acute kidney injury. If unavoidable: monitor creatinine and potassium within 1–2 weeks.

Aspirin-Exacerbated Respiratory Disease (AERD)
Samter Triad — affects ~10–20% of adults with asthma
Asthma + Nasal Polyps + NSAID-triggered bronchoconstriction
  • Mechanism: COX-1 block → LOX shunting → cysteinyl leukotriene surge → bronchospasm (30–180 min)
  • Triggered by: any COX-1 inhibiting NSAID (ibuprofen, naproxen, indomethacin, aspirin, ketorolac, diclofenac)
  • Safe alternative: celecoxib (COX-2 selective — does not trigger LOX shunting)
  • Also safe: acetaminophen at standard doses
High-Priority Drug Interactions
NSAIDs + Anticoagulants
2–4× GI bleed risk — use PPI, minimize NSAID duration
Triple Whammy
NSAID + ACE/ARB + diuretic → acute kidney injury — avoid
NSAIDs + Lithium
Raise lithium levels 10–60% — check levels within 5–7 days
NSAIDs + High-dose MTX
Impaired renal excretion — do not use within 24 hours of oncology MTX
NSAIDs + SSRIs
Additive platelet dysfunction → GI bleed — use PPI
Ibuprofen + Aspirin
Blocks aspirin COX-1 acetylation — take aspirin first; prefer naproxen
Special Populations
Contraindicated from 20 weeks
Pregnancy
  • ≥20 wk: oligohydramnios risk
  • ≥28 wk: ductal arteriosus closure
  • Use acetaminophen instead
  • Low-dose aspirin safe (preeclampsia prevention)
Prefer topical diclofenac
Elderly (≥65 years)
  • Reduced renal reserve
  • Impaired mucosal repair
  • Polypharmacy risk
  • CNS effects (indomethacin)
Avoid eGFR <30; caution 30–60
CKD & Cirrhosis
  • eGFR <30: contraindicated
  • Cirrhosis Child-Pugh B/C: contraindicated
  • Use acetaminophen (reduced dose in cirrhosis)