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CNS DRUGS

An introduction to pharmacy

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CNS DRUGS

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  1. OVERVIEW OF NERVOUS SYSTEM DRUGS Dr. Kenneth Orimma B.Sc., M.Sc., M.B.B.S, D.I.R, D.M(Doctor of Medicine) Psychiatry

  2. NERVOUS-SYSTEM DRUGS • Nervous system is divided into central nervous system and peripheral nervous system • The drugs used in treatment of nervous system disorders can be group into -Peripheral Nervous System Targets -Central Nervous System Targets:

  3. NERVOUS-SYSTEM DRUGS Peripheral Nervous System Targets: 1. TRPV1R Receptors (Vanilloid Receptors) • The transient receptor potential cation channel subfamily V member 1 (TrpV1), also known as the capsaicin receptor and the vanilloid receptor 1, is a protein that, in humans, is encoded by the TRPV1gene. • This protein is a member of the TRPV group of transient receptor potential family of ion channels. • TRPV1 is an element used by the mammalian somatosensory system. • It is a nonselective cation channel that may be activated by a wide variety of exogenous and endogenous physical and chemical stimuli. • Sensitive to H+/Capsaicin/Heat/Mechanical): § Capsaicin:Activates TRPV1R Receptors on C-Fibres → Causes Substance-P release → Depletes the terminal of Substance-P (A Peptide) → leading to a period of Analgesia while Sub-P is re-synthesizedEg: Topical Arthritis Cream

  4. NERVOUS-SYSTEM DRUGS 2. Prostanoid Receptors (Sensitive to Prostaglandins): § Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) – (Aspirin/Ibuprofen) • Anti-Inflammatory Analgesic: →↓Prostaglandin Production by inhibiting the enzyme Cyclo-Oxygenase (COX) → ↓Prostaglandin-Mediated Hypersensitivity of Nociceptive Neurons § COX-2 Inhibitors – (Celebrex) • Anti-Inflammatory Analgesic: • More specific than NSAID’s – Target COX-2 Enzyme – Less Side-Effects • They ↓Prostaglandin Production by inhibiting the enzyme Cyclo-Oxygenase-2 (COX-2) →↓Prostaglandin-Mediated Hypersensitivity of Nociceptive Neurons

  5. NERVOUS-SYSTEM DRUGS 3. Opioid Receptors: § Opioid Drugs – (Codeine, Morphine, Fentanyl): acts on the Distal Nerve Endings – (Periphery): →Opens K+ Channels → K+- Efflux → Hyperpolarisation

  6. NERVOUS-SYSTEM DRUGS CENTRAL NERVOUS TARGET DRUGS 1. Drugs that act by Pain-Gate Mechanism Opioid Drugs – (Codeine, Morphine, Fentanyl): • On Proximal Nerve Ending – (Spinal Cord): →Mimic Autoreceptors → Closure of Ca+ Channels → ↓Ca+- Mediated NT Release • On Periaqueductal Grey Matter (PAG) – (Brain): →Remove Inhibition of PAG (Activates PAG) → Activates NRM → Inhibits Dorsal Horn Synapse

  7. NERVOUS-SYSTEM DRUGS 2. Descending Inhibitory Neurons: Tri-Cyclic Antidepressants: o Low-Dose Tri-Cyclic Anti-Depressants → block re-uptake of NE, Serotonin, & Encephalins in Dorsal Horn Synapse → Maintained Inhibition of Nociceptive Transmission

  8. NERVOUS-SYSTEM DRUGS 3. Potential Efferent Nervous System Drug Targets: ACh-Receptors: o Nicotinic Agonists: § Drugs which Enhance the Action @ the Nicotinic ACh-Receptor § Eg: Nicotine/ACh(Endogenous)/CarbacholTopical(Constricts Pupils → Treats Glaucoma) o Nicotinic Antagonists (Anti-Nicotinics): § Drugs which Inhibit the Action @ the Nicotinic ACh-Receptor § Eg: Suxamethonium(Muscle Relaxant)/Champix (Helps Quit Smoking)

  9. NERVOUS-SYSTEM DRUGS 4. Neuromuscular Blockers: § Clinically used as a Paralytic/Muscle-Relaxant in Ventilated General Anaesthesia Non-Depolarising – Act as Competitive nAChR-Antagonists at the ACh-Receptors → Prevents ACh from binding nAChRs • Antidote for overdose: Acetyl-Cholinesterase Inhibitor → ↑[ACh] • Side Effects: Ganglion Block → o Hypotension o Bradycardia

  10. NERVOUS-SYSTEM DRUGS Depolarising – Act as nicotinic AChR-Agonists →Maintained depolarisation @ the NMJ → Loss of Electrical Excitability • Side Effects: o Bradycardia o Hyperkalaemia (Due to K+ Release from Muscle) o ↑Intraocular Pressure (Due to Contraction of Extraocular Muscle) o Prolonged Paralysis (If Acetyl-Cholinesterase is Abnormal – ) o Malignant Hyperthermia (If SR-Ca+ Channel is Mutated • Special Cautions: o Prolonged Paralysis can occur If Acetyl-Cholinesterase is Abnormal/Mutated/Absent/Inhibited o Malignant Hyperthermia can occur if SR-Ca+ Channel is Mutated → Intense Muscle Spasms & ↑Body Temp → High Mortality

  11. NERVOUS-SYSTEM DRUGS 5. Acetyl Cholinesterase: Acetyl-Cholinesterase Inhibitors: § Drugs that Inhibit the Cholinesterase Enzyme from degrading ACh in the Synapse § Eg: Physostigmine/Organophosphates→ Prolonged Action of ACh in the Synapse→ ↑[ACh] in the Synapse § Used to Treat Myasthenia Gravis § Also used as Nerve Gas (Chemical Warfare) o Eg:: Tacrine – An Acetyl-Cholinesterase Inhibitor: § Originally used to treat Alzheimer’s Disease § Alzheimer’s Dx: is characterised by loss of cholinergic neurons in Basal Nuclei) § Hence, an AChE-Inhibitor compensates for loss of Cholinergic Signalling

  12. NERVOUS-SYSTEM DRUGS 6. Choline Reuptake Transporter: Choline Reuptake Inhibitor: § Drugs that inhibit Choline Reuptake by Blocking the Choline Transporter → Prolonged Action of ACh in the Synapse → ↑[ACh] in the Synapse

  13. NERVOUS-SYSTEM DRUGS 7. Drugs that work by blocking exocytosis of ACh Vesicles: o Eg: Botulinum Toxin: § Blocks Exocytosis of ACh-Vesicles from Cholinergic Nerve Terminals § - Proteolytically degrades the adhesion proteins required for vesicle fusion with PM

  14. NERVOUS-SYSTEM DRUGS Autonomic Nervous System Drugs

  15. NERVOUS-SYSTEM DRUGS Sympathetic: o Sympathomimetics: § Drugs that Mimic the Effects of the Sympathetic NS § Directly Acting (Adrenergic Agonists): • α-Adrenergic-Agonists • β-Adrenergic-Agonists § Indirectly Acting (NESynthesis/Storage/Release/Uptake/Degradation): • ↑NE-Synthesis • ↑Vesicular Repackaging of NE (rather than destruction) • ↑NE-Release • Blocking NE-Reuptake from synapse • ↓NE-Degradation (By inhibiting Mono-Amine-Oxidase)

  16. NERVOUS-SYSTEM DRUGS Parasympathetic: o Parasympathomimetic: (“Muscarinic Agonists”): § Drugs that Mimic the Effects of the Parasympathetic NS § Most are Muscarinic Agonists § Effects: • Bradycardia & Hypotension • Contraction of Smooth Muscle (Eg: Bronchoconstriction) • Increased GI Motility (Peristalsis) • Increased Secretions (Salivary/Lacrimal/Bronchial/Intestinal) • Pupillary Constriction (Useful in Closed-Angle Glaucoma → ↓IOP)

  17. NERVOUS-SYSTEM DRUGS Parasympatholytics: (Muscarinic Antagonists): § Drugs that Inhibit the Parasympathetic NS Effects: Tachycardia • Relaxation of Smooth Muscle (Eg: Bronchial/Biliary/Urinary tracts) • Decreased GI Motility (Peristalsis) • Decreased Secretions (Salivary/Lacrimal/Bronchial/Sweat Glands) • Pupillary Dilation (Dangerous for Closed-Angle Glaucoma → ↑IOP)

  18. NERVOUS-SYSTEM DRUGS THE END THANK YOU VERY MUCH

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