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Drugs that are tertiary parasympatholytics:
Selective muscarinic-receptor blockers (anticholinergics/parasympatholytics):
-M1 blocker: pirenzepine
-M4 blocker: tropicamide
Mydriatic (ophthalmic) parasympatholytics:
-atropine (long duration of action: 3-5d)
-tropicamide (12hr; selective M4 blocker)
Mech of action of atropine:
competitive antagonist to Ach on muscarinic receptors
-a drug that reversibly binds to the receptor at the same site as the agonist and prevents the agonist from binding to its receptor
What are the pharmacological effects of atropine on the eye?
-cycloplegia (paralysis of the ciliary mm---> loss of visual accommodation)
-decreased lacrimation (dry eye; may become easily inflamed)
*don't use in glaucoma patients
Pharmacological effects of atropine on the resp sys:
-bronchodilation (in muscarinic receptors only) and reduced secretions from the nose, pharynx, bronchi
-decreases mucociliary clearance
Pharmacological effects of atropine on the CVS:
-tachycardia (initial bradycardia)
-clinically sig if given IV
-vasoconstriction (slight increase in bp)
Pharmacological effects of atropine on the GIT:
-decreased GIT motility and salivary and gastric secretions
-causes relaxation of the wall of the gallbladder and contraction of the sphincter
Pharmacological effects of atropine on the urinary bladder:
-relaxation of wall of the urinary bladder and detrusor muscle and contraction of sphincter
*can be used to treat urinary incontinence
Pharmacological effect of atropine on the CNS:
-weak stim at therapeutic doses due to poor penetration
-can cause convulsive seizures
How well is atropine distributed?
-widely distributed, but has a poor penetration at the brain at therapeutic doses (causes weak stim)
What are the therapeutic uses for atropine?
-bradycardia and AV block (incomplete)
-mydriatic and cycloplegia
-preanesthetic (decreases bronchial and exocrine gland secretions)
-organophosphate and other cholinesterase inhibitor poisoning
-mushroom (Amanita spp) poisoning
What are the adverse effects of atropine?
-tachycardia (if given IV)
-blurred vision, mydriasis, and cycloplegia
-nausea, vomiting (is an alkaloid and can irritate oral mucosa), GIT hypomotility (can be used as an antispasmodic) and constipation (ileus)
-dry mouth (xerostomia)
What are the contraindications/precautions against using atropine?
-acute myocardial infarction (ischemic heart dz)
-closed angle glaucoma
-diarrhea, GIT obstruction or infection
-urinary tract obstruction (stones)
What other drugs interact with atropine?
-other anticholinergics (additive/summation effect)
-antihistamines (1st gen)
-phenothiazines (and butyrophenones)
-tricyclic antidepressants (TCA)
-opioid antidiarrheals (for symp treatment of diarrhea)
-digoxin (causes tachycardia)
How does scopolamine/hyoscine affect the emetic center?
it is used in motion sickness (this is NOT a therapeutic use for atropine)
How does scopolamine/hyoscine affect the eye?
it is used as an ophthalmic agent to induce cycloplegia and for iritis and uveitis
What is aminopentamide approved to treat?
it is approved as an antispasmodic to treat GI spasm in dogs and cats
What are the side effects of aminopentamide?
generally similar to atropine:
-blurred vision, mydriasis, cycloplegia
-nausea, vomiting, GI hypomotility (antispasmodic), constipation (ileus)
-dry mouth (xerostomia)
What is oxybutynin used for?
used as adjunctive therapy for detrusor hyperreflexia in dogs and cats (treatment of urinary incontinence)
How does glycopyrroate compare to atropine?
-more potent than atropine as an antispasmodic and in inhibiting secretions
-less potent than atropine on the CVS
-has less side effects than atropine
-has longer duration of action than atropine
What is glycopyrroate used for?
-preanesthetic (better than atropine)
-GIT antispasmodic (more potent than atropine)
What is the duration of action for glycopyrroate?
~2-4 hours post injection (longer duration than atropine: 60-90 mins)
What is propantheline used for?
used as a GIT antispasmodic agent and for urinary incontinence (neurogenic bladder)
How well does ipratropamine bronchodilate?
it is more potent as a bronchodilator than atropine (but less potent than B2-agonists)
How does ipratropamine affect salivary secretion?
it causes much less decrease in salivary secretions than atropine (there are more salivary secretions than when using atropine; atropine causes dry mouth)
How do side effects caused by ipratropamine compare to atropine?
ipratropamine has less side effects than atropine
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