Antimuscarinic Agents
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Antimuscarinic Agents

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Antimuscarinic Agents Antimuscarinic Agents Presentation Transcript

  • Antimuscarinic agents
    • These are the drugs which blocks the actions of Ach especially mediated through muscarinic receptor.
    • Classification
    • Natural alkaloids
    • Atropine
    • Hyoscine (Scopolamine)
    • Semi synthetic derivatives
    • Homatropine
    • Homatropine methyl bromide
    • Atropine methonitrate
    • Hyoscine methyl bromide
    • Hyoscine butyl bromide
    • Ipratropium bromide
    • Tiotropium bromide
    • Synthetic compounds
    • a) Mydriatics
    • Cyclopentolate
    • Tropicamide
    • b) Antisecretory -antispasmodics
    • Θ Quaternary ammonium compounds
    • Propantheline
    • Oxyphenium
    • Clidinium
    • Pipenzolate
    • Glycopyrrolate
    • Θ Tertiary amines
    • Dicyclomine
    • Pirenzepine
    • Telenzepine
    • Oxybutynin
    • Flevoxate
    • c) Antiparkinsonian drugs
    • Benzhexol
    • Procyclidine
    • Biperiden
    • Benztropine
    • Cycrimine
    • Ethopropazine
    • Miscellaneous
    • Tricyclic antidepressants
    • Phenothiazines
    • Antihistaminics
    • Disopyramide
    • M/A
    • Belladonna alkaloids like atropine block the muscarinic effects of Ach.
    • This is a competitive inhibition which is reversed by an increase in the concentration of Ach at the muscarinic neuroeffector site.
    • They do not interfere with the release of Ach at the cholinergic nerve endings.
    • Pharmacological actions
    • CNS
    • At low doses atropine do not cross BBB.
    • At higher doses it produce CNS stimulant action.
    • ` Hyoscine produce CNS depressant effect even at low doses.
    • Atropine stimulates many medullary centers – vagal, respiratory, vasomotor.
    • It depresses vestibular excitation and has antimotion sickness property.
    • It suppresses the tremor and rigidity of parkinsonism by blocking the cholinergic over activity in basal ganglia.
    • In high doses cause cortical excitation, restlessness, disorientation, hallucinations and delirium followed by respiratory depression and coma.
    • CVS
    • In heart, M 2 receptor is blocked by atropine in S.A node and A.V node leads to tachycardia.
    • It also blocks muscarinic autoreceptors on vagal nerve endings augmenting ach release, this leads to
    • Predominant bradycardia and finally tachycardia.
    • Blood vessels
    • Atropine at high doses has direct vasodilatory effect and also enhances the release of histamine. This leads to hypotension.
    • Ach vasodilatation
    • Eye
    • Topical instillation of atropine causes mydriasis, lack of light reflex and cycloplegia lasting 7-10days.
    • This results in photophobia and blurring of near vision.
    • Intra occular tension tends to rise, specially in narrow angle glaucoma.
    ־ Atropine
    • Smooth muscle
    • All visceral smooth muscles are relaxed by atropine (M 3 blocked).
    • The tone & contraction of stomach and intestine are reduced; the passage of chyme is slowed – constipation may occur, spasm may be relieved.
    • Atropine causes bronchodilatation and reduces air way resistance, specially in COPD and asthma patients.
    • It has a relaxant action on ureter and urinary bladder;
    • Urinary retention may occur in older males with BPH.
    • relaxation of biliary tract and uterus is minimal.
    • Glands
    • Atropine decreases sweat, salivary, tracheobronchial and lachrymal secretion (M 3 blockade).
    • Skin & eye become dry, talking and swallowing may be difficult.
    • It also decreases G.I secretions like pepsin, mucous, HCl etc.
    • Body temperature
    • Rise in body temperature occurs at higher doses. It is due to both inhibition of sweating as well as stimulation of temperature regulating centre in the hypothalamus.
    • Local anesthetic effect
    • Atropine has a mild anesthetic action on the cornea.
    • Pharmacokinetics
    • A rapid by G.I.T and cornea on topical application.
    • D crosses BBB and produces CNS effects
    • M in liver (50%)
    • E urine, as metabolite or unchanged form
    • t ½ 3 – 4hrs.
    • Preparations & dose
    • Atropine sulfate : 0.6 – 2mg I.M; I.V
    • 10 μ g/kg for children
    • 1 – 2% topically in eye.
    • Hyoscine hydrobromide : 0.3 – 0.5mg oral, I.M, also transdermal patch.
    • Therapeutic uses
    • As antisecretory
      • Pre anesthetic medication
      • when irritant general anesthetics (ether) are used, prior administration of anticholinergics ( atropine, hyoscine, glycopyrrolate) are imperative to check increased salivary and tracheobronchial secretions.
      • Peptic ulcer
      • atropine drugs decrease gastric secretion and afford symptomatic relief in peptic ulcer (but it is not using nowadays due to their side effects as well as the entry of H2 – blockers).
      • In pulmonary embolism
      • To check excessive sweating or salivation . E.g.:- parkinsonism.
    • As antispasmodic
      • Intestinal and renal colic, abdominal cramps.
      • Nervous and drug (reserpine, guanethidine) induced diarrhea, functional diarrhea.
      • Spastic constipation, irritable colon.
      • Pylorospasm, gastric hyper motility, gastritis, nervous dyspepsia.
      • To relieve urinary frequency and urgency, enuresis in children
    • Bronchial asthma, asthmatic bronchitis, COPD
    • These drugs are less effective than adrenergic drugs.
    • Ipratropium bromide is used in COPD. It has additive bronchodilator action with adrenergic drugs and theophylline.
    • As mydriatic & cycloplegic
      • Diagnostic :- for testing error of refraction, both mydriasis and cycloplegia are needed. Tropicamide is used widely.
      • To facilitate fundoscopy only mydriasis is needed.
      • Therapeutic :- atropine is used in the treatment of iritis, iridocyclitis, choroiditis, keratitis and corneal ulcer.
    • As cardiac vagolytic
    • Atropine is useful in counteracting bradycardia and partial heart block in selected patients where increased vagal tone is responsible, e.g.:- in some cases of M.I, digitalis toxicity.
    • For central action
      • Parkinsonism
      • These drugs are used only in mild cases because they are less effective than L-dopa.
      • Motion sickness
      • Hyoscine is most effective.
      • 3. Hyoscine has been used to produce sedation and amnesia during labour and to control maniacal states.
    • To antagonize muscarinic effects of drugs & poisons
    • Atropine is an antidote for anti chE and early mushroom poisoning.
    • It also block muscarinic actions of neostigmine used for myasthenia gravis, decurarization or cobra envenomation.
    • Contraindications
    • Θ Narrow iridocorneal angle – may precipitate acute congestive glaucoma.
    • Θ In patients with BPH – urinary retention may occur.
    • Interactions
    • Absorption of most drugs is slowed.
    • L-dopa dose should be increased in presence of these drugs, because the absorption slower and greater peripheral degradation occurs, thereby less of it reaches the brain.
    • But in case of tetracycline and digoxin absorption may be increased due to longer transit time in the G.I.T.
    • Antacids interfere with absorption of anticholinergics.
    • Antihistaminics, tricyclic antidepressants, phenothiazines, pethidine have anticholinergic property – additive side effects with atropinic drugs.
    • MAO inhibitors interfere with metabolism of anticholinergic antiparkinsonian drugs - delirium may occur.