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Cholinergic antagonists
Anti- muscarinic agents
sites of action• 1. Secretions by salivary, bronchial and sweat
glands.• 2. The eye and cardiac responses mediated by
the vagus.• 3. Urinary bladder and GI tract.• 4. Gastric secretions.
Naturally occurring
• Atropine ( belladonna )
• Scopolamine
• Homatropine
• ATROPINE – high affinity for muscarinic receptors. acts both centrally and peripherally.
• Mydriasis, cycloplegia.• Eneuresis in children• Low doses- bradycardia.• High doses—tachycardia• Dilates cutaneous vasculature
• Atropine uses• In ophthalmology –mydriatic/ cycloplegic• Spastic disorders of GI and lower urinary tract.• To treat OP poisoning• To suppress respiratory secretions prior to
surgery.
Synthetic quaternary ammonium antimuscarinic agents.
• Ipratropium
• Propantheline
Synthetic tertiary amine muscarinic antagonists
• Cyclopentolate
• Tropicamide
• Dicyclomine
• Pirenzipine
CNS• Due to its greater lipid solubility, scopolamine
has significant CNS effects even at low therapeutic doses.
• An adjunct for anesthesia due to an ability to decrease short term memory.
• Motion sickness (scopolamine)• Antipsychotic therapy: used to treat the
extrapyramidal symptoms
Eye
• Mydriasis
• Refract the eye during ophthalmic examinations.
• Caution : glaucoma
Heart
• Low doses initially produce bradycardia, but later doses produce tachycardia.
• Some times in Surgery/catheterization
Lung
• Broncho -dilation: Ipratropium• Mainly used as inhalation in treating asthma and
COPD.• Atropine prior to surgery will decrease the
respiratory secretions
GI tract
• Salivary secretions decrease
• Can cause dry mouth and difficulty in swallowing
• Only Pirenzepine has some potency to decrease hyperacidity..
Other uses
• With an opioid to relax the ureter in renal colic.
• To increase the capacity and decrease the frequency of bladder contractions, i.e.enuresis in children.
• To decrease the frequency of urination in spastic paraplegia.
Toxic effects• decreased concentration and memory• drowsiness• sedation• excitation• ataxia• asynergia• disorientation• hallucinations• coma
ATROPINE PSYCHOSIS
• Disorientation, confusion, recent loss of memory, agitation, incoherent speech, restlessness, hallucinations, anxiety and delirium.
• Treatment – symptomatic only and discontinue the drug immediately.
Therapeutic uses of muscarinic antagonists
• 1. Premedication• · Atropine• · Given before operations to prevent unwanted M
stimulation.• · Want to eliminate bronchial secretions (don't want the
patient to choke on their own secretions)• · Want to block vagal stimulation to the heart and lungs
(want to keep airways open)• · During induction of anesthesia, there may be excessive
vagal stimulation, which we want to eliminate.
• Anticholinesterase toxicity• Toxicity due to over dose of physostigmine and
other anticholinesterases
• Atropine is used to treat this condition by blocking all M receptors.
• 2. Antispasmodic• · Hyoscine N butyl Bromide• · A quaternary derivative• · Treats colic• 3. Bronchodilator (asthma)• · Ipratropium• · A quaternary derivative• · Given by inhalation, get a local effect
• Homatropine• · Much shorter action than atropine• · It is the drug of choice when doing
investigations of the eye, since it dilates the pupil for a short time only.
• 4.Treatment of peptic ulcers• · Pirenzepine• · Selective M1 antagonist• · Not as good as H2 antagonists (e.g.
cimetidine) or proton pump inhibitors (e.g. omeprazole)
• 5. Parkinson's disease • · Benztropine, trihexiphenidyl
also used to treat the extrapyramidal symptoms due to Antipsychotic drugs
• 6. Motion sickness
· Hyoscine, scopolamine
• REMEMBER • S --- salivation• L --- lacrimation• U --- urination• D --- diaphoresis• G --- GI• E --- Eye & emesis
GANGLIONIC BLOCKERS
• NICOTINE
• TRIMETHAPHAN
• MECAMYLAMINE
SITE OF ACTION
• ALL NICOTINIC RECEPTORS
• IN ANS ( BOTH SNS AND PNS )• IN CNS
NICOTINE
DOSAGE
• LOW DOSE
• HIGH DOSE
GANGLION
• STIMULATION
• BLOCK
CNS/ NICOTINE
• LOW DOSE- EUPHORIA,RELAXATION
• HIGH DOSE- central respiratory paralysishypotension- medullary paralysis
PERIPHERAL EFFECTS
• COMPLEX• HR RAISES• B.P.- RAISES• GIT- MOTILITY RAISES
OTHERS
• TRIMETHAPHAN- SHORT ACTING• HTN EMERGENCIES
• used in surgery, particularly neurosurgery, to produce a relatively bloodless operative field (controlled hypotension).
• MECAMYLAMINE- LONG ACTINGCHR. CASES of HTN
Neuromuscular Blocking Drugs
Mainly during surgery to produce complete muscle relaxation, without giving higher anesthetic doses.
Neuro muscular blocking drugs• Atracurium• Doxacurium• Mivacurium • Pancuronium• Rocuronium• Succinylcholine• Tubocurarine• Vecuronium
Atracurium• safe in renal failure, used in critically ill patients
for mechanical ventilation. • Short duration of action – so suitable for short
surgical procedures.
Rocuronium & Succinylcholine • Rapid onset of action – so used mainly in
tracheal intubation in patients with gastric contents.
Vecuronium – short duration of action , so used in short surgical procedures.
Imp side effects
• Tubocurarine – induce histamine release and also lower B.P.
• Pancuronium – Increased H.R.• Succinylcholine – malignant hyperthermia,
hyperkalemia and increased Intraocular pressure.