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Anticholinergic Drugs

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Anticholinergic Drugs

  1. 1. Anticholinergic Drugs Dr. Pramod P Bhalerao (M.D.) Asst. Professor Dept. of Pharmacology
  2. 2. Introduction • Anticholinergic drugs block actions of Acetylcholine on autonomic effectors and in the CNS exerted through muscarinic receptors.
  3. 3. Pharmacological actions (Atropine as prototype) • 1. CNS • It depresses vestibular excitation and has antimotion sickness property. The site of this action is not clear—probably there is a cholinergic link in the vestibular pathway, or it may be exerted at the cortical level. • By blocking the relative cholinergic overactivity in basal ganglia, it suppresses tremor and rigidity of parkinsonism.
  4. 4. Pharmacological actions (Atropine as prototype) • 2. CVS • Heart • The most prominent effect of atropine is tachycardia. • It is due to blockade of M2 receptors on the SA node through which vagal tone decreases HR.
  5. 5. Pharmacological actions (Atropine as prototype) • 3. Eye • Topical instillation of atropine causes mydriasis, abolition of light reflex and cycloplegia lasting 7–10 days. • This results in photophobia and blurring of near vision.
  6. 6. Pharmacological actions (Atropine as prototype) • 4. Smooth muscles • All visceral smooth muscles that receive parasympathetic motor innervation are relaxed by atropine (M3 blockade).
  7. 7. Pharmacological actions (Atropine as prototype) • 4. Smooth muscles of GIT • Tone and amplitude of contractions of stomach and intestine are reduced; the passage of chyme is slowed—constipation may occur, spasm may be relieved.
  8. 8. Pharmacological actions (Atropine as prototype) • 4. Smooth muscles of bronchi • Atropine causes bronchodilatation and reduces airway resistance, especially in COPD and asthma patients.
  9. 9. Pharmacological actions (Atropine as prototype) • 4. Smooth muscles of Urinary Tract • Atropine has relaxant action on ureter and urinary bladder. • Beneficial for increasing bladder capacity and controlling detrusor hyperreflexia in neurogenic bladder/enuresis.
  10. 10. Pharmacological actions (Atropine as prototype) • 5. Glands • Atropine markedly decreases sweat, salivary, tracheobronchial and lacrimal secretion (M3 blockade). • Skin and eyes become dry, talking and swallowing may be difficult.
  11. 11. Pharmacological actions (Atropine as prototype) • 6. Body temperature • Rise in body temperature. • Due to inhibition of sweating.
  12. 12. Atropine substitutes • They are divided into 2 subtypes: • Quaternary compounds • Tertiary amines
  13. 13. Quaternary compounds • These have certain common features— • Incomplete oral absorption. • Poor penetration in brain and eye; central and ocular effects are not seen after parenteral/ oral administration. • Elimination is generally slower; majority are longer acting than atropine.
  14. 14. Quaternary compounds • 1. Hyoscine butyl bromide- used for esophageal and gastrointestinal spastic conditions. • 2. Atropine methonitrate- 2.5–10 mg oral, i.m.; for abdominal colics. • 3. Ipratropium bromide- Used for chronic obstructive pulmonary disease (COPD). • 4. Tiotropium bromide- Used for COPD. • 5. Clidinium- antisecretory-antispasmodic – Used for Irritable bowel syndrome, colic. • 6. Glycopyrrolate- potent and rapidly acting antimuscarinic lacking central effects.
  15. 15. Tertiary amines • 1. Dicyclomine- antispasmodic • 2. Valethamate- as visceral antispasmodic,urinary, biliary, intestinal colic.
  16. 16. Vasicoselective drugs • 1. Oxybutynin- relatively selective for M1/M3 subtypes. Used for overactive bladder. • 2. Tolterodine- relatively M3 selective muscarinic antagonist has preferential action on urinary bladder; less likely to cause dryness of mouth and other anticholinergic side effects.
  17. 17. Mydriatics • 1. Homatropine- Instilled in the eye, it acts in 45–60 min. Mydriasis lasts 1–3 days. It often produces unsatisfactory cycloplegia in children who have high ciliary muscle tone. • 2. Cyclopentolate- It is potent and rapidly acting; mydriasis and cycloplegia occur in 30– 60 min. Mydriasis last about a day. • 3. Tropicamide- It has the quickest (20–40 min) and briefest (3–6 hours) action, but is a relatively unreliable cycloplegic.
  18. 18. Antiparkinsonian drugs • Central Anticholinergics: • Trihexyphenidyl (Benzhexol), • Biperiden. • They act by reducing the unbalanced cholinergic activity in the striatum of parkinsonian patients. Parkinsonism
  19. 19. Uses of Anticholinergics • I. As antisecretory • II. As antispasmodic • III. Bronchial asthma, COPD • IV. As mydriatic and cycloplegic • V. As cardiac vagolytic • VI. For central action • VII. To antagonise muscarinic effects of drugs and poisons
  20. 20. I. As antisecretory • 1. Preanaesthetic medication • Atropinic drugs prevent laryngospasm by reducing respiratory secretions that reflexly predispose to laryngospasm. • Vasovagal attack during anaesthesia can also be prevented. • 2. Pulmonary embolism • These drugs benefit by reducing pulmonary secretions evoked reflexly by embolism.
  21. 21. II. As antispasmodic • 1. Intestinal and renal colic, abdominal cramps: • 2. To relieve urinary frequency and urgency, enuresis in children. Oxybutynin, tolterodine and flavoxate have demonstrated good efficacy, but dry mouth and other anticholinergic effects are dose limiting.
  22. 22. III. Bronchial asthma, COPD • Inhaled ipratropium bromide has been found to be specially effective in COPD, though less so in bronchial asthma. • Ipratropium blocks bronchoconstriction mainly in the larger airways.
  23. 23. IV. As mydriatic and cycloplegic • (i) Diagnostic • For testing error of refraction, both mydriasis and cycloplegia are needed.Tropicamide having briefer action has now largely replaced homatropine for this purpose. • These drugs do not cause sufficient cycloplegia in children: more potent agents like atropine or hyoscine have to be used. Atropine ointment (1%) applied 24 hours and 2 hours before is often preferred for children below 5 years. Cyclopentolate drops are an alternative.
  24. 24. IV. As mydriatic and cycloplegic • (ii) Therapeutic • Because of its long lasting mydriatic-cycloplegic and local anodyne (pain relieving) action on cornea, atropine is very valuable in the treatment of iritis, iridocyclitis, choroiditis, keratitis and corneal ulcer. It gives rest to the intraocular muscles and cuts down their painful spasm. • Atropinic drugs alternated with a miotic prevent adhesions between iris and lens or iris and cornea and may even break them if already formed.
  25. 25. V. As cardiac vagolytic • Atropine is useful in counteracting sinus bradycardia and partial heart block in selected patients where increased vagal tone is responsible, e.g. in some cases of myocardial infarction and in digitalis toxicity.
  26. 26. VI. For central action • 1. Parkinsonism • 2. Motion sickness • Hyoscine is the most effective drug for motion sickness. • The drug should be given prophylactically (0.2 mg oral), because administration after symptoms have setin is less effective; action lasts 4–6 hours.
  27. 27. VII. To antagonise muscarinic effects of drugs and poisons • Atropine is the specific antidote for anti ChE and early mushroom poisoning. Anticholinestrase Insecticide
  28. 28. Side effects and toxicity • Datura Poisoning
  29. 29. Side effects and toxicity • Belladonna poisoning • May occur due to drug overdose or consumption of seeds and berries of belladonna/datura plant. • Manifestations are due to exaggerated pharmacological actions. • Dry mouth, • Difficulty in swallowing and talking. • Dry, flushed and hot skin (especially over face and neck), fever, • Difficulty in micturition, decreased bowel sounds. • Dilated pupil, photophobia, blurring of near vision, palpitation.
  30. 30. Treatment of Belladona poisoning • If poison has been ingested, gastric lavage should be done with tannic acid. • The patient should be kept in a dark quiet room. • Cold sponging or ice bags are applied to reduce body temperature. • Physostigmine 1–3 mg s.c. or i.v. antagonises both central and peripheral effects. • Other general measures (maintenance of blood volume, assisted respiration, diazepam to control convulsions) should be taken as appropriate.
  31. 31. Contraindications • In individuals with a narrow iridocorneal angle—may precipitate acute congestive glaucoma. • Caution is advocated in elderly males with prostatic hypertrophy— urinary retention can occur.
  32. 32. Thank You

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