Unit 5: CNS Drugs Part II (Analgesics & Anesthetics)

Semester 4

BP402T

Introduction to CNS Drugs Part II (Analgesics & Anesthetics)

Continuing the study of CNS agents, this unit focuses on profound pain management and surgical anesthesia. It starts with General Anesthetics—volatile halogenated hydrocarbons (like Halothane) and IV agents (like Ketamine). The core of the unit is the Narcotic Analgesics, focusing deeply on the SAR of the natural phenanthrene alkaloid Morphine, and synthetic derivatives like Fentanyl. Finally, it explores Non-Narcotic Analgesics and Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), detailing the synthesis of everyday medications like Ibuprofen and Mefenamic Acid.

Syllabus & Topics

1General Anesthetics: Inhalation anesthetics (Halothane, Methoxyflurane).
2General Anesthetics: Ultra-short acting barbiturates and Dissociative anesthetics (Ketamine).
3Narcotic Analgesics: Morphine and related compounds (Codeine, Heroin).
4SAR of Morphine analogues.
5Narcotic antagonists: Naloxone, Naltrexone.
6NSAIDs: Salicylates, Arylalkanoic acids (Diclofenac, Indomethacin), Profens (Ibuprofen).
7NSAIDs: Anthranilates (Mefenamic acid), Oxicams, Para-aminophenol derivatives (Paracetamol).
8Synthesis of Halothane, Ketamine hydrochloride, Fentanyl citrate, Ibuprofen, Mefenamic acid.

Learning Objectives

Correlate the halogenation of volatile anesthetics with their safety and potency.

Outline the complete Structure-Activity Relationship of the Morphine molecule.

Explain the function of Narcotic Antagonists in reversing opioid overdose.

Classify NSAIDs chemically and map out the synthetic pathways for Ibuprofen and Mefenamic acid.

Frequently Asked Questions (FAQs)

Q1. Why Does the Morphine Structure Require a Specific Stereochemistry to Be an Active Analgesic?

Morphine binds to highly stereoselective μ (mu) opioid receptors. It possesses a rigid T-shaped conformation due to its pentacyclic ring system. Any alteration in stereochemistry, such as removal of the phenolic –OH group or change in the orientation of the piperidine ring, prevents proper docking into the receptor binding site and leads to a significant loss of analgesic potency.

Q2. What is the Role of Ketamine in Anesthesia?

Ketamine produces dissociative anesthesia, a state in which the patient feels detached from their body and surroundings without complete loss of consciousness. Structurally classified as an arylcyclohexylamine, it acts as a non-competitive antagonist at the NMDA receptor.

Q3. Why is Methadone Used in Opioid Substitution Therapy?

Methadone is a synthetic opioid that binds to the same μ-opioid receptors as morphine but lacks the rigid multi-ring structure. It is widely used in opioid substitution therapy because it is orally active and has a long half-life, which helps prevent withdrawal symptoms without producing the rapid euphoric high associated with heroin.

Q4. What is the Common Mechanism of Action for NSAIDs like Aspirin and Ibuprofen?

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) such as Aspirin and Ibuprofen inhibit cyclooxygenase enzymes (COX-1 and COX-2). By blocking COX activity, they prevent the synthesis of prostaglandins from arachidonic acid, thereby reducing pain, fever, and inflammation.