Nsaids and cox selectivity

Clinical use in anaesthesia (how to apply safely)

Role: opioid-sparing analgesia (multimodal), particularly effective for inflammatory and bone pain; limited for severe visceral pain alone
- Typical perioperative uses: MSK trauma/orthopaedics, post-tonsillectomy (local policy re bleeding), renal colic, dysmenorrhoea, dental pain
- Less useful: neuropathic pain; caution in major abdominal surgery with high anastomotic risk (institution-dependent)
Patient selection: balance GI/renal/bleeding/CV risks against analgesic benefit
- High GI risk: age >65, previous ulcer/bleed, H. pylori, steroids, SSRIs, anticoagulants/antiplatelets, high-dose NSAID
- High renal risk: CKD, dehydration, sepsis, heart failure, cirrhosis/ascites, perioperative hypovolaemia, concurrent ACEi/ARB + diuretic ("triple whammy")
- High bleeding risk: thrombocytopenia/platelet dysfunction, major surgery with critical bleeding consequences, concurrent anticoagulation; avoid around neuraxial procedures per local/ASRA-type guidance
- High CV risk: established IHD/CVA/PAD, uncontrolled hypertension, heart failure; avoid COX-2 selective in high CV risk if alternatives exist
Practical perioperative approach
- Give only if euvolaemic and haemodynamically stable; avoid in ongoing bleeding, sepsis with AKI risk, or significant renal hypoperfusion
- Use lowest effective dose for shortest duration; consider PPI co-prescription in high GI risk
- If aspirin for secondary prevention: avoid ibuprofen around aspirin dosing (can blunt antiplatelet effect); consider alternative NSAID or dosing separation

Core pharmacology: COX enzymes and prostanoids

Arachidonic acid → (cyclo-oxygenase) → prostaglandins (PGE2, PGI2) and thromboxane (TXA2)
COX-1: constitutive (“housekeeping”)—gastric mucosal protection, platelet TXA2 synthesis, renal blood flow autoregulation (esp. stressed states)
COX-2: inducible at inflammation (pain, fever); also constitutive in kidney, brain, endothelium (PGI2 production)
Analgesic/antipyretic effects mainly via reduced PGE2 (peripheral and central sensitisation) and reduced inflammatory mediator amplification

Mechanism of NSAIDs and COX selectivity

Most NSAIDs reversibly inhibit COX-1 and/or COX-2; aspirin irreversibly acetylates COX-1 (platelets) → antiplatelet effect for lifespan of platelet (~7–10 days)
COX selectivity is relative (dose-dependent): higher doses often reduce selectivity
Clinical implications of selectivity
- More COX-1 inhibition → more platelet inhibition and more GI mucosal injury (ulcer/bleed)
- More COX-2 selectivity → less GI toxicity and minimal platelet effect, but higher thrombotic risk (↓ endothelial PGI2 with preserved platelet TXA2)
- Renal effects occur with both COX-1 and COX-2 inhibition (COX-2 is constitutive in kidney) → selectivity does not eliminate AKI risk

Adverse effects (exam framework: GI, renal, platelet/bleeding, respiratory, CV, hepatic, skin, pregnancy)

GI: dyspepsia, gastritis, ulceration, perforation, bleeding (risk ↑ with COX-1 inhibition, age, prior ulcer, steroids/SSRIs/anticoagulants)
Renal: reduced afferent arteriolar vasodilation (↓ PGE2/PGI2) → ↓ GFR; sodium/water retention, oedema, hypertension; hyperkalaemia; papillary necrosis (chronic)
- Highest risk when renal perfusion is prostaglandin-dependent: hypovolaemia, sepsis, CHF, cirrhosis, CKD, elderly
Platelets/bleeding: non-selective NSAIDs inhibit platelet COX-1 reversibly → prolonged bleeding time while drug present; COX-2 selective have minimal platelet effect
Respiratory: NSAID-exacerbated respiratory disease (NERD/AERD)—bronchospasm, rhinitis, urticaria/angioedema (COX-1 inhibition shunts to leukotrienes)
Cardiovascular: increased thrombotic events (MI/stroke) with COX-2 selective and some non-selective (notably diclofenac); fluid retention can worsen heart failure; can increase BP and blunt antihypertensive therapy
Hepatic: transaminitis; rare severe hepatotoxicity (drug-specific, e.g., diclofenac association)
Skin/hypersensitivity: rash, urticaria; rare SJS/TEN (drug-specific risk)
Pregnancy/fetus: avoid in 3rd trimester—premature closure of ductus arteriosus, oligohydramnios (fetal renal impairment), maternal/postpartum bleeding; may impair ovulation/fertility

Common perioperative NSAIDs (key comparisons)

Ibuprofen: non-selective (COX-1>COX-2 at usual doses); good analgesic, relatively lower GI risk than some; important interaction with aspirin antiplatelet effect
Diclofenac: relatively COX-2 preferring but not selective; effective analgesic; higher CV thrombotic risk signal; hepatic enzyme rise more common
Naproxen: non-selective; comparatively lower thrombotic risk signal vs others (still GI/renal risks)
Ketorolac: potent non-selective; higher bleeding and renal risk—use short course and careful selection
Indometacin: non-selective; used for PDA closure (neonates) and some headache syndromes; higher CNS/GI side effects
COX-2 selective (e.g., celecoxib, etoricoxib; parecoxib IV as prodrug of valdecoxib): less GI ulceration and minimal platelet effect; similar renal effects; increased thrombotic risk in susceptible patients

COX selectivity: what it means for bleeding, GI and CV risk (exam synthesis)

Bleeding: COX-1 inhibition ↓ TXA2 → impaired platelet aggregation; COX-2 selective spare platelets → preferred when surgical bleeding risk is a concern (but still consider overall haemostasis and local policy)
GI: COX-1 inhibition reduces protective gastric prostaglandins → ulcer/bleed; COX-2 selective reduce (not abolish) GI risk; PPI reduces upper GI complications
CV thrombosis: COX-2 inhibition reduces endothelial PGI2 (anti-platelet/vasodilator) while platelet TXA2 remains → prothrombotic tendency; risk increases with baseline CV disease and longer/higher dosing
Renal: both COX-1 and COX-2 contribute to renal prostaglandins; COX-2 selective do not protect against AKI, fluid retention, or hypertension

Drug interactions worth stating in viva

Anticoagulants/antiplatelets (warfarin, DOACs, aspirin, clopidogrel): additive bleeding risk; NSAIDs increase GI bleeding risk substantially
SSRIs/SNRIs: increased GI bleeding risk (platelet serotonin depletion) + NSAID effect
ACEi/ARB + diuretic + NSAID (“triple whammy”): afferent constriction + efferent dilation + volume depletion → AKI risk
Lithium: NSAIDs can increase lithium levels (reduced renal clearance)
Methotrexate: reduced renal clearance → toxicity (dose-dependent relevance; still mention)
Aspirin + ibuprofen: ibuprofen can competitively inhibit aspirin access to platelet COX-1 if taken first/close together → reduced cardioprotection

Explain the mechanism of action of NSAIDs and how COX selectivity alters clinical effects.

Aim: link COX-1/COX-2 physiology to analgesia and adverse effects.

NSAIDs inhibit cyclo-oxygenase (COX) → ↓ prostaglandins (PGE2, PGI2) and thromboxane (TXA2)
Analgesia/antipyresis: mainly via ↓ PGE2 → reduced peripheral sensitisation and central nociceptive facilitation; anti-inflammatory via reduced prostanoid-mediated vasodilation and oedema
COX-1 inhibition: ↓ gastric mucosal protection + ↓ platelet TXA2 → GI ulcer/bleed and increased bleeding tendency
COX-2 selectivity: less GI toxicity and minimal platelet effect, but ↑ thrombotic risk due to ↓ endothelial PGI2 with preserved platelet TXA2
Renal adverse effects occur with both (COX-2 is constitutive in kidney) → selectivity does not remove AKI/fluid retention risk

Compare COX-1 and COX-2: where they are found and what they do.

A common Primary FRCA pharmacology viva stem.

COX-1: constitutive—gastric mucosal prostaglandins, platelet TXA2 synthesis, renal autoregulation (especially in hypoperfusion)
COX-2: inducible in inflammation—pain, fever; also constitutive in kidney, brain, vascular endothelium (PGI2 production)
Clinical link: COX-1 blockade → GI/bleeding; COX-2 blockade → anti-inflammatory/analgesic with less platelet effect but potential thrombosis

Why do COX-2 selective NSAIDs increase cardiovascular risk?

You must mention the prostacyclin–thromboxane balance.

Endothelium produces PGI2 (prostacyclin) via COX-2 → vasodilation and inhibition of platelet aggregation
Platelets produce TXA2 via COX-1 → platelet aggregation and vasoconstriction
Selective COX-2 inhibition reduces PGI2 while leaving TXA2 relatively unopposed → prothrombotic state (MI/stroke risk), especially in patients with baseline atherosclerotic disease
Additional contributors: hypertension and fluid retention can worsen CV outcomes

Describe the renal effects of NSAIDs and when they are most dangerous perioperatively.

Frame as prostaglandin-dependent renal perfusion.

Mechanism: ↓ renal prostaglandins (PGE2/PGI2) → reduced afferent arteriolar vasodilation → ↓ renal blood flow and GFR
Physiological consequences: AKI, sodium/water retention, oedema, hypertension; hyperkalaemia (reduced renin/aldosterone effects)
Highest risk states: hypovolaemia, sepsis, heart failure, cirrhosis, CKD, elderly; perioperative hypotension/bleeding
Drug interaction: ACEi/ARB + diuretic + NSAID (“triple whammy”) markedly increases AKI risk

A patient has aspirin for secondary prevention. What is the issue with giving ibuprofen?

This has appeared repeatedly as a pharmacology viva/SAQ concept.

Aspirin irreversibly acetylates platelet COX-1 → sustained reduction in TXA2
Ibuprofen reversibly occupies COX-1 active site; if taken first/close together it can prevent aspirin binding → reduced antiplatelet (cardioprotective) effect
Management: avoid ibuprofen where possible, use alternative NSAID, or separate dosing (aspirin first with adequate interval per local policy/pharmacy advice)

List contraindications (or strong cautions) to perioperative NSAID use.

Give a structured answer: allergy/bleeding/GI/renal/CV/pregnancy.

Hypersensitivity: previous NSAID-induced bronchospasm/urticaria/angioedema (NERD/AERD)
Active GI ulceration or recent GI bleed; high-risk patients without gastroprotection
Significant renal impairment or high AKI risk state (hypovolaemia, sepsis, CHF, cirrhosis)
Bleeding risk/platelet dysfunction; caution with anticoagulants/dual antiplatelet therapy
Severe heart failure, uncontrolled hypertension; established high CV thrombotic risk (avoid COX-2 selective particularly)
Pregnancy: avoid especially 3rd trimester (ductal closure, oligohydramnios)

You are asked: 'Do COX-2 selective drugs affect bleeding?' Give a clear answer.

A common viva trap: distinguish platelet function from surgical bleeding risk overall.

Platelets primarily express COX-1; COX-2 selective NSAIDs have minimal effect on platelet aggregation and bleeding time
Therefore they are less likely to increase bleeding than non-selective NSAIDs, but overall bleeding depends on surgery, haemostasis, and other drugs
They still share renal effects (fluid retention/AKI) and CV thrombotic concerns

Outline the main differences between aspirin and other NSAIDs.

High-yield comparison for FRCA pharmacology.

Aspirin irreversibly inhibits COX (especially platelet COX-1) → antiplatelet effect lasts platelet lifespan (7–10 days)
Most other NSAIDs inhibit COX reversibly → platelet effects are transient and depend on drug presence
Aspirin at low dose is used for antiplatelet therapy; at analgesic doses behaves like non-selective NSAID with GI/renal risks

Discuss NSAID use in asthma.

Expect to mention NERD/AERD and leukotriene shunting.

Most asthmatics tolerate NSAIDs, but a subset have NSAID-exacerbated respiratory disease (NERD/AERD)
Mechanism: COX-1 inhibition reduces prostaglandins and shifts arachidonic acid metabolism towards leukotrienes → bronchoconstriction and nasal symptoms
Management: avoid non-selective NSAIDs in known NERD; consider alternatives (paracetamol at usual doses, opioids, regional); COX-2 selective may be better tolerated but still caution

SAQ-style: 'List the adverse effects of NSAIDs.' Provide a structured answer.

Use a systems-based list and link to COX where relevant.

GI: dyspepsia, ulceration, bleeding, perforation
Renal: AKI, sodium/water retention, hypertension, hyperkalaemia; papillary necrosis (chronic)
Haematological: platelet dysfunction and bleeding (non-selective); rare anaemia secondary to GI loss
Respiratory/immune: bronchospasm (NERD), urticaria/angioedema, anaphylactoid reactions
CV: MI/stroke risk (COX-2 selective and some non-selective), worsening heart failure, increased BP
Hepatic: transaminitis, rare severe hepatitis
Pregnancy/fetus: ductal closure, oligohydramnios; maternal bleeding

Previous FRCA-style stem: 'Explain why NSAIDs can precipitate acute kidney injury in a hypovolaemic patient.'

A classic physiology-pharmacology crossover question.

In hypovolaemia, renal perfusion pressure falls and the kidney relies on prostaglandin-mediated afferent arteriolar vasodilation to maintain GFR
NSAIDs inhibit COX → ↓ PGE2/PGI2 → afferent vasoconstriction → reduced renal blood flow and GFR → AKI
Risk is amplified by concurrent ACEi/ARB (efferent dilation) and diuretics (volume depletion)

Previous FRCA-style stem: 'Why might a COX-2 selective NSAID be chosen postoperatively, and what are the trade-offs?'

You need to show balanced risk assessment.

Reasons to choose: similar analgesia with less GI ulceration and minimal platelet inhibition → potentially less surgical bleeding impact
Trade-offs: renal adverse effects remain (AKI/fluid retention), and thrombotic risk may be higher—avoid/limit in high CV risk patients
Practical: use lowest effective dose, shortest duration; consider PPI if GI risk; reassess daily