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🧪 NSAIDs — Med Chem Easy Guide

🔑 What Are NSAIDs? (The Big Picture)

A-A-A = Analgesic + Antipyretic + Anti-inflammatory

• No CNS depression
• No physical dependence
• No abuse liability
• Weaker pain relief (except inflammatory pain)
• Also called: non-narcotic / non-opioid / aspirin-like analgesics

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🔧 Mechanism of Action — The CORE Concept

Arachidonic acid  →[COX enzyme]→  Prostaglandins (PGs)
                    ↑
              NSAIDs BLOCK this

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⚠️ Side Effects — Why Do They Happen?

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📋 Classification — The 7 Classes (Easy to Remember)

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💊 Drug-by-Drug Key Points

🅐 ASPIRIN (Acetylsalicylic Acid)

• Unique action: Irreversibly acetylates COX-1 AND COX-2 → permanent block
• Most selective for COX-1 (especially in platelets)
• Low dose (75–100 mg/day): Cardioprotective → blocks TXA2 → prevents platelet aggregation → prevents heart attacks & strokes
• Baby aspirin = 81 mg
• Side effects: Ulcers, GI bleeding, tinnitus (ringing in ears)
• Metabolism: Salicylic acid → excreted as salicyluric acid (glycine conjugate = major metabolite), also as glucuronides
• Alkaline urine increases excretion (remember for overdose treatment!)

Aspirin trick for exam: "Aspirin is the only NSAID that covalently (irreversibly) binds COX — all others are reversible!"

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🅑 SODIUM SALICYLATE

• Less potent than aspirin
• Less GI irritation
• Used in aspirin-hypersensitive patients

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🅒 SULINDAC (Arylacetic acid class)

• Prodrug — inactive itself, activated in the liver
• Converted to active methyl sulfide metabolite (potent COX inhibitor)
• Has a chiral sulfoxide but marketed as racemate (because it's converted to achiral active form anyway)
• Z isomer more active than E isomer
• Long half-life due to extensive enterohepatic circulation

Memory trick: "SULindac = SUL-fate prodrug → liver activates it"

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🅓 ZOMEPIRAC

• Was a pyrole acetic acid derivative
• Withdrawn from market — caused fatal anaphylactic reaction (rare but deadly)

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🅔 ARYL PROPANOIC ACIDS (Ibuprofen, Naproxen class)

• All members (except oxaprozin) have a chiral carbon
• Only S-enantiomer is active (inhibits COX)
• Most are sold as racemates, but the inactive R-enantiomer is converted → S by an enzyme (2-arylpropionyl-CoA epimerase) in the body

Memory trick: "S-enantiomer = Superactive"

• Similar efficacy to aspirin in RA, but fewer side effects
• Used in primary dysmenorrhea (period pain)
• ⚠️ Warning: Ibuprofen + Aspirin together = ibuprofen BLOCKS aspirin's cardioprotective effect (reversibly competes at platelet COX-1)

• Marketed as pure (S)-enantiomer
• Highly protein bound → displaces other protein-bound drugs (drug interaction risk!)

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🅕 FENAMATES (Mefenamic acid, Meclofenamic acid, Diclofenac)

• Lower GI irritation risk compared to other NSAIDs
• All share a common structural feature (N-aryl anthranilic acid core)

• Hepatic benzylic hydroxylation of the 3'-methyl group → 2 inactive metabolites

• Most hepatotoxic NSAID (unusual — others mainly cause GI/kidney issues)
• Can cause severe liver damage (rare, idiosyncratic)
• Reason: forms reactive benzoquinone imines → normally detoxified by glutathione
• Metabolism: CYP2C9/3A4 → 4-hydroxy-diclofenac (major metabolite)

Memory trick: "Diclofenac = Danger to liver"

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🅖 PIROXICAM (Oxicam class)

• Metabolism: CYP2C9 → 5-hydroxy-piroxicam (major metabolite)
• Several prodrugs synthesized (ampiroxicam, droxicam, pivoxicam) to reduce GI irritation

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🅗 ACETAMINOPHEN / PARACETAMOL — The Odd One Out

• Has analgesic + antipyretic actions but NO anti-inflammatory, NO antiplatelet
• Does NOT cause GI side effects (safe for stomach)
• Mechanism: possibly blocks a brain-specific COX-3 enzyme (still debated!)
• Works centrally (brain), not peripherally like other NSAIDs

Acetaminophen → [CYP2E1/CYP3A4] → NAPQI (toxic reactive metabolite)
                                           ↓
                              Glutathione neutralizes NAPQI (safe)
                                           ↓
                    If glutathione is depleted (overdose) → LIVER DAMAGE

• Alcohol INCREASES toxicity because alcohol induces CYP2E1 and CYP3A4 → more NAPQI formed
• Antidote: N-acetylcysteine (replenishes glutathione)

Memory trick: "Para-cetamol = PARAsitic on the liver when overdosed + alcohol"

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🅘 PYRAZOLONE DERIVATIVES

• Phenylbutazone: Used in animals now (too toxic for humans); metabolized to oxyphenbutazone (active metabolite) via aromatic hydroxylation
• Antipyrine (Phenazone): Analgesic/antipyretic only

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🧠 Quick Exam Summary Table

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🗂️ Most Likely Exam Questions (Quick Answers)

1. Which NSAID irreversibly inhibits COX? → Aspirin
2. Which enantiomer of propionic acid NSAIDs is active? → S-enantiomer
3. Why does paracetamol overdose cause liver failure? → NAPQI formation (toxic metabolite) overwhelms glutathione
4. Why does alcohol worsen paracetamol toxicity? → Alcohol induces CYP2E1/CYP3A4 → more NAPQI
5. Which NSAID is a prodrug? → Sulindac (converted to methyl sulfide in liver)
6. Which NSAID is most hepatotoxic? → Diclofenac (forms benzoquinone imines)
7. Why do NSAIDs cause GI ulcers? → Block PGE2 → less mucus + more acid
8. What is the major metabolite of salicylic acid? → Salicyluric acid (glycine conjugate)
9. Which NSAID lacks anti-inflammatory action? → Acetaminophen (Paracetamol)
10. Which NSAID was withdrawn due to fatal anaphylaxis? → Zomepirac

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