Mechanism of Action of Ketorolac

Introduction

Ketorolac is a potent nonsteroidal anti-inflammatory drug (NSAID) primarily used for short-term management of moderate to severe pain, especially postoperative pain. It is often considered an alternative to opioids due to its strong analgesic effect without causing respiratory depression. Ketorolac belongs to the acetic acid class of NSAIDs and is known for its significant analgesic and anti-inflammatory properties.

Mechanism of Action (Step-wise)

1. Non-selective Cyclooxygenase (COX) Inhibition
   Ketorolac inhibits both COX-1 and COX-2 enzymes.
2. Blockade of Arachidonic Acid Conversion
   COX enzymes normally convert arachidonic acid into prostaglandins and thromboxanes. Ketorolac blocks this pathway.
3. Reduction in Prostaglandin Synthesis
   Decreased production of prostaglandins (especially PGE2) reduces inflammation, pain, and fever.
4. Analgesic Effect
   Lower prostaglandin levels decrease sensitization of peripheral nociceptors, leading to strong pain relief.
5. Anti-inflammatory Effect
   Reduction in prostaglandins leads to decreased vasodilation, edema, and inflammatory response.
6. Antipyretic Effect
   In the hypothalamus, reduced prostaglandin levels help lower elevated body temperature.
7. Platelet Function Inhibition
   By inhibiting COX-1, ketorolac decreases thromboxane A2 (TXA2), impairing platelet aggregation (reversible effect).

Pharmacokinetics

• Administration: Oral, intramuscular, intravenous
• Absorption: Rapid and complete
• Protein Binding: High (~99%)
• Metabolism: Hepatic
• Half-life: ~5–6 hours
• Excretion: Renal (primarily as metabolites)

Clinical Uses

• Short-term management of moderate to severe pain
• Postoperative pain
• Renal colic
• Musculoskeletal pain
• Adjunct to reduce opioid requirement

Adverse Effects

• Gastrointestinal irritation, ulcers, bleeding
• Renal impairment
• Increased bleeding risk (due to platelet inhibition)
• Nausea and vomiting
• Headache and dizziness

Comparative Analysis

Ketorolac is one of the most potent NSAIDs and is often used as an opioid-sparing analgesic. Unlike opioids, it does not cause respiratory depression but carries a higher risk of gastrointestinal bleeding and renal toxicity.

MCQs

1. Ketorolac primarily inhibits which enzyme?
   a) Lipoxygenase
   b) Cyclooxygenase
   c) Phospholipase A2
   d) Adenylate cyclase
   Answer: b) Cyclooxygenase
2. Ketorolac belongs to which class?
   a) Opioid
   b) NSAID
   c) Steroid
   d) Antibiotic
   Answer: b) NSAID
3. Main analgesic mechanism:
   a) Sodium channel blockade
   b) Prostaglandin inhibition
   c) Dopamine increase
   d) GABA activation
   Answer: b) Prostaglandin inhibition
4. Which prostaglandin is mainly reduced?
   a) PGE2
   b) PGF2α
   c) TXA2
   d) PGD2
   Answer: a) PGE2
5. Platelet aggregation is affected due to:
   a) Increased TXA2
   b) Decreased TXA2
   c) Increased prostacyclin
   d) Increased serotonin
   Answer: b) Decreased TXA2
6. Ketorolac is commonly used for:
   a) Chronic hypertension
   b) Severe pain
   c) Diabetes
   d) Asthma
   Answer: b) Severe pain
7. Major adverse effect:
   a) Hepatotoxicity
   b) GI bleeding
   c) Ototoxicity
   d) Neurotoxicity
   Answer: b) GI bleeding
8. Ketorolac differs from opioids because it:
   a) Causes addiction
   b) Causes respiratory depression
   c) Does not cause respiratory depression
   d) Acts on μ receptors
   Answer: c) Does not cause respiratory depression
9. Route NOT commonly used:
   a) Oral
   b) IV
   c) IM
   d) Inhalation
   Answer: d) Inhalation
10. Duration of therapy should be:
    a) Long-term
    b) Short-term only
    c) Lifelong
    d) Intermittent only
    Answer: b) Short-term only

FAQs

1. What is the mechanism of action of ketorolac?
   It inhibits COX enzymes, reducing prostaglandin synthesis and producing analgesic effects.
2. Why is ketorolac considered potent?
   Because it provides strong analgesia comparable to opioids.
3. Can ketorolac cause bleeding?
   Yes, due to inhibition of platelet aggregation.
4. Why is ketorolac used short-term only?
   Because of high risk of GI and renal toxicity.
5. Does ketorolac cause respiratory depression?
   No, unlike opioids.
6. Is ketorolac anti-inflammatory?
   Yes, it has anti-inflammatory properties.

References

• Goodman & Gilman’s The Pharmacological Basis of Therapeutics – NSAIDs
• Katzung: Basic and Clinical Pharmacology – Nonsteroidal Anti-inflammatory Drugs
• Tripathi: Essentials of Medical Pharmacology
• Harrison’s Principles of Internal Medicine – Pain Management

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