Parasympatholytics (anticholinergics, cholinoceptor-blocking drugs)

Created by Harviejm 

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What class of drugs are parasympatholytics?

-cholinergic antagonists (anti-muscarinics)

What type of molecules are parasympatholytics?

tertitary or quaternary antimuscarinics

Are tertiary molecs good or poor penetrators?

good penetrators

Drugs that are tertiary parasympatholytics:

-atropine
-hyoscine (scopolamine)
-dicyclomine
-aminopentamide
-oxybutynin

Drugs that are quaternary parasympatholytics:

-glycopyrrolate
-propantheline
-ipratropium

Selective muscarinic-receptor blockers (anticholinergics/parasympatholytics):

-M1 blocker: pirenzepine
-M4 blocker: tropicamide

Mydriatic (ophthalmic) parasympatholytics:

-atropine (long duration of action: 3-5d)
-scopolamine (3d)
-cyclopentolate (2d)
-homatropine (1d)
-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?

-mydriasis
-cycloplegia (paralysis of the ciliary mm---> loss of visual accommodation)
-increased IOP
-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 is atropine administered?

-topically, orally, injection (IV, IM, SC), inhalation

How well is atropine absorbed?

-readily absorbed (good penetrator: tertiary)

How well is atropine distributed?

-widely distributed, but has a poor penetration at the brain at therapeutic doses (causes weak stim)

Where is atropine metabolized and excreted?

-metabolized in the liver
-excreted in urine and milk

What is the duration of action for injected atropine?

60-90 mins

What is the duration of action for atropine given orally?

4-6 hours

What is the duration of action for atropine given topically on the eye?

up to 5 days

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)
-dry eye
-urinary retention

What are the contraindications/precautions against using atropine?

-tachycardia
-acute myocardial infarction (ischemic heart dz)
-closed angle glaucoma
-diarrhea, GIT obstruction or infection
-urinary tract obstruction (stones)
-myasthenia gravis

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)

What type of molecule is scopolamine (hyoscine)?

tertiary

How does scopolamine/hyoscine affect CNS at therapeutic doses?

it prod CNS depression

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 type of molecule is dicyclomine?

tertiary

How does dicyclomine compare to atropine?

it has less systemic effects than atropine

What is dicyclomine used for?

it is an antispasmodic (ex. IBS)

What type of molecule is aminopentamide?

tertiary

What is aminopentamide approved to treat?

it is approved as an antispasmodic to treat GI spasm in dogs and cats

In which forms is aminopentamide available?

oral tabs and injectable (IM, SC)

What are the side effects of aminopentamide?

generally similar to atropine:
-tachycardia
-blurred vision, mydriasis, cycloplegia
-nausea, vomiting, GI hypomotility (antispasmodic), constipation (ileus)
-dry mouth (xerostomia)
-urinary retention

What type of molecule is oxybutynin?

tertiary

What is oxybutynin used for?

used as adjunctive therapy for detrusor hyperreflexia in dogs and cats (treatment of urinary incontinence)

What type of molecule is glycopyrroate?

quaternary

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)
-bronchodilator
-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 type of molecule is propantheline?

quaternary

What type of receptors does propantheline block?

*both ganglionic nicotinic AND muscarinic (unique)

What is propantheline used for?

used as a GIT antispasmodic agent and for urinary incontinence (neurogenic bladder)

In which types of patients should propantheline NOT be used?

in patients w/ myasthenia gravis

What type of molecule is ipratropium?

quaternary

How well does ipratropamine bronchodilate?

it is more potent as a bronchodilator than atropine (but less potent than B2-agonists)

How does ipratropamine affect the mucocilliary escalator?

it does not alter mucocilliary clearance

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

How is ipratropamine used?

-used alone or combined with albuterol as a bronchodilator
-used intranasally for rhinitis

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