19 terms

Antimuscarinic Drugs (Muscarinic Agonists): Atropine and Atropine-Like Agents (Lecture 6)

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Muscarinic Antagonists are also called...
Anticholinergic drugs
Antimuscarinic drugs
Muscarinic blockers (blocks muscarine receptors)
Atropine-like drugs
Atropine
Prototype muscarinic antagonist. A belladonna alkaloid that selectively and competitively blocks muscarinic subtype of ACh receptor. NO EFFECT on nicotinic (or adrenergic) receptors. Many drugs have atropine-like (antimuscarinic) actions, uses, side effects and contraindications.
What is a belladonna alkaloid?
belladonna = "beautiful woman"
alkaloid = "drug derived from plants"
Morphine is the active metabolite of what drug?
Heroin, an alkaloid derived from poppy opiates
What are the main Autonomic effects of Antimuscarinics?
Generally the opposite of those caused by Muscarinic agonists (or activation of the PNS, or of the sympathetic nerves to sweat glands)
Main Responses to Antimuscarinics
Eye: pupils dilate (paralysis of accommodation-cannot adjust lens to read up close)
Bronchi: bronchodilation
Heart: <3 rate increases
GI tract: constipation
Bladder: urine retention
Exocrine glands, including sweat glands: decreses secretions
Uses of Antimuscarinics on the Eye
Used to dilate pupil and paralyze accommodation for eye exams.
Accommodation
Focusing the eye on nearby objects occurs via PNS activation, which contracts ciliary muscle, allowing lens to thicken. Antimuscarinics prevent this.
Cycloplegia
Paralysis of accommodation of the eye. Antimuscarinics create this effect.
Other Uses of Antimuscarinics
*treat bowel or bladder hypermotility (urinary frequency/incontinence)
*treat bradycardia (excessive slowing of <3 rate)
*to dry secretions (mainly saliva and mucus as in allergies, common cold, or preop)
*treat overdoses of muscarinic agonists, AChEIs (Acetylcholinesterase Inhibitors)
*treat Parkinson's Disease (this is based on actions in CNA, not periphery)
Side Effects of Antimuscarinics
Dry mouth (reduced salivary secretions)
Blurred vision
Photophobia ("day blindness" from dilated pupils that can't constrict as they should in bright light)
Contraindications of Antimuscarinics
*Narrow-angle glaucoma, in which dilation of the pupil is unwanted and potentially dangerous
*Heart rate is already high
*Gut: constipation or hypomotility
*Bladder/urinary tract (weakened bladder musculature or obstruction, for example in prostatic hypertrophy)
Hypertrophied Prostate
Enlarged prostate gland, obstructing urethra. May necessitate acute urine retention for men which requires hospitalization and a Foley catheter!
When should you be extra cautious about using either Muscarinic Agonists OR Muscarinic Blockers?
Urethral obstruction
Effects of Antimuscarinic Poisoning
Peripheral Autonomic signs/symptoms:
*Dry as a Bone
*Blind as a Bat
*Hot as a Furnace (antimuscarinic overdoses can create profound fever, partially due to the fact that you're NOT sweating)
*Red as a Beet (dry, prevalent in neck/face, "atropine flush"

CNS (brain) signs/symptoms:
*Mad as a Hatter
True or false: Antimuscarinic poisoning is a uncommon event.
False! Antimuscarinic poisoning is a common event.
What is the treatment for Antimuscarinic Poisoning
Physostigmine + Symptomatic supportive care!
Is atropine itself used frequently or infrequently?
Atropine itself is actually used infrequently, but there are other drugs that have strong atropine-like actions.
Drugs that have Atropine-like actions
*Many older antihistamines (ex: diphenhydramine)
*Some antipsychotics (ex: chlorpromazine)
*Some antidepressants (ex: amitriptyline, a "tricyclic" antidepressant
*some antiParkinson drugs