Anticholinergic drugs
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Lecture covers the pharmacology of anticholinergic drugs. Includes classification, therapeutic uses, adverse effects of anticholinergics. Atropine has been described as prototype drug.
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Anticholinergic drugs
- 1. Anti-cholinergic drugs Dr Naser Ashraf Tadvi
- 2. Objectives • Classify anticholinergic drugs • Describe the mechanism of action, pharmacological actions, therapeutic uses and adverse effects of anticholinergic drugs • Describe the treatment of atropine toxicity
- 3. Classification of antimuscarinic drugs Natural alkaloids • Atropine • Hyoscine (Scopolamine ) Semisynthetic derivatives • Atropine Methonitrate • Homatropine • Hyoscine butylbromide • Ipratropium bromide • Tiotropium bromide Synthetic Compounds Antisecretory- antispasmodics Quaternary Comps. • Propantheline • Oxyphenonium • Clidinium • Glycopyrrolate Tertiary amines • Dicyclomine • Valethamate • Pirenzepine Mydriatics Cyclopentolate Tropicamide Vasicoselective • Oxybutinin • Tolterodine • Flavoxate • Darifenacin • Solifenacin • Trospium Antiparkinsonian • Trihexyphenidyl (Benzhexol) • Procyclidine • Biperiden • Benztropin
- 4. Mechanism of action of anticholinergic drugs
- 5. Pharmacological actions of atropine • CNS: – Mild CNS stimulant action in therapeutic doses – Large doses- excitement, restlessness, hallucinations – Antiparkinsonian effect by reducing cholinergic overactivity in basal ganglia – Antimotion sickness effect by suppressing vestibular disturbances
- 6. Pharmacological actions of atropine • CVS : – Low doses of atropine cause bradycardia due to blockade of presynaptic M1 receptors on vagal nerve endings (Inhibit release of Ach) – Moderate to high doses cause tachycardia due to blockade of M2 receptors in heart – ↑ SA and AV nodal conduction ↓ PR interval
- 7. • Glands – All secretions under cholinergic influence reduced (Due to M3 receptor block) – Except Milk and Bile secretion – Skin and mucus membrane become dry Pharmacological actions of atropine
- 8. • Smooth muscles – GIT: • ↓Tone and motility • ↑ Sphincter tone may cause constipation • Relaxes smooth muscle of gall bladder – Genitourinary tract • Relaxes detrusor muscle of bladder & ↑ tone of trigone and sphincter (Retention of urine) – Bronchi • Relaxes bronchial smooth muscle • ↓ secretion & muco-ciliary clearance (mucus plug may form) Pharmacological actions of atropine
- 9. Pharmacological actions of atropine Paralysis of constrictor pupillae (Blockade of M3 receptors ) Passive Mydriasis Paralysis of ciliary muscle (Blockade of M3 receptors ) Cycloplegia (loss of accommodation) Atropine action on eye on topical administration
- 10. Pharmacokinetics of anticholinergic drugs • Absorption : – Atropine, scopolamine other tertiary amines well absorbed • Distribution: – except quaternary compounds rest drugs are widely distributed. • Metabolism: – 50% atropine & 80 % scopolamine metabolized by liver as conjugates • Excretion – 50% atropine excreted unchanged in urine – t ½ = 3 hours
- 11. Therapeutic uses of anticholinergic drugs 1. Parkinsonism 2. Motion sickness 3. Bronchial Asthma & COPD 4. Vagolytic to treat sinus bradycardia, partial heart block 5. Antispasmodic in dysmennorhoea 6. Intestinal, renal, biliary colic 7. Relieve bladder spasm after uro-surgery, Urinary incontinence
- 12. 8. Ophthalmic uses – Mydriatic and cycloplegic for refraction testing – Mydriatic for fundoscopy – Iridocyclitis used alternatingly with miotics to break the adhesions between iris and lens 9. Preanaesthetic medication – Atropine or glycopyrrolate used to prevent vagal bradycardia and laryngospasm Therapeutic uses of anticholinergic drugs
- 13. 10. Sialorrhoea 11. Organo-phosporus Poisoning 12. some type of mushroom poisoning 13. Along with neostigmine to counter its muscarinic effects Therapeutic uses of anticholinergic drugs
- 14. Adverse effects • Dry mouth, difficulty swallowing • Photophobia, blurred vision • May precipitate acute congestive glaucoma • Retention of urine • Constipation • Restlessness, excitement • Tachycardia, palpitations
- 15. Atropine toxicity • Hot as a hare: hyperpyrexia • Red as beetroot: cutaneous vasodilation • Dry as a bone: dry skin • Blind as a bat: mydriasis and cycloplegia • Mad as hatter: restlessness, excitement
- 16. Treatment of atropine poisoning • Hospitalization • Gastric lavage • Tepid sponging • Diazepam to control convulsions • Antidote for atropine poisoning is physostigmine 1-4 mg injected slowly.
- 17. Contraindications of atropine • Acute congestive glaucoma • Elderly patients (More prone for urinary retention)
- 18. Classification of anticholinergics according to clinical use S.N Use Drug 1 Ophthalmic use Cyclopentolate, tropicamide, homatropine 2 Antispasmodic Dicyclomine, Hyoscine methyl bromide, propantheline 3 Urinary antispasmodic Oxybutinin, flavoxate, darifenacin, trospium 4 Bronchodilation Ipratropium, tiotropium 5 Parkinsonism benztropine, biperidine, benzhexol
- 19. Summary • Classification • Pharmacological actions • Therapeutic uses • Adverse effects • Contraindications
- 20. What is the rationale of • Use of atropine in preanesthetic medication • Preference of physostigmine over neostigmine in treatment of OPP • Scopolamine in motion sickness
- 21. What are differences between • Atropine and scopolamine • Ocular actions of atropine and ephedrine
- 22. Name • Specific M1 receptor blocker • Specific M3 blockers
- 23. Why • Atropine used in children for mydriasis • Tropicamide/ cyclopentolate preferred in adult patients for mydriasis
Notas do Editor
- Large doses- excitement, restlessness, hallucinations, agitation, medullary paralysis, coma and death
- Large doses- excitement, restlessness, hallucinations, agitation, medullary paralysis, coma and death Atropine has minimal action on ventricles which are innervated by adrenergic fibres Adequate dose of atropine can suppress many type of reflex vagal cardiac slowing or asystole as occurring due to inhalation of irritant vapors stimulation of carotid sinus , pressure in eye balls, peritoneal stimulation, or injection of contrast medium during cardiac catheterization it can also negate cardiac slowing due to drugs like anticholinesterases, digpxin,
- Secretions like sweat, salivary, nasal, throat, bronchial, gastric, lacrimal etc.
- Secretions like sweat, salivary, nasal, throat, bronchial, gastric, lacrimal etc. The action of atropine on urinary bladder is useful in relieving the urinary spasm due to inflammation, surgery, and certain neurogenic conditions,. Overactive bladder is a neurogenic bladder disorder.
- Absorption: Atropine, scopolamine other tertiary amines well absorbed from the gut and across conjunctival membranes, if prepared in a suitable vehicle, these can be absorbed by the transdermal route example scopolamine transdermal patch Distribution: except quaternary compounds rest drugs are widely distributed, scopolamine rapidly and fully distributed in CNS and has greater effects than most of the other antimuscarinic drugs Metabolism: 50% atropine & 80 % scopolamine metabolized by liver as conjugates . Some animal species as black rabbits are resistant to atropine actions because they possess specific enzyme, atropine esterase which degrades atropine faster than in human Half life of atropine is 3 hours the effects of atropine decline rapidly in all organs except eye where the effects last about 72 hours or more
- Physostigmine preferred over neostigmine