Cholinergic Drugs Flashcards
What are the two types of cholinergic receptors and where are the found?
Nicotinic
- In ganglia of both SNS and PNS
- Also in adrenal medulla to release epinephrine
- Skeletal muscle neuromuscular junctions
- CNS
- Stimulated by nicotine
Muscarinic
- In effector tissues of PNS (smooth muscle, cardiac cells, glands)
- CNS
- Stimulated by a poisonous mushroom compound muscarine
What is the function of cholinergic activators?
To stimulate cholinergic pathways in PNS and the cholinergic system in CNS
Also known as agonists or “parasympathomimetics”
Mimic the effects of cholinergic neurotransmitter acetylcholine (ACh)
What’s the difference between direct-acting and indirect-acting cholinergic agonists?
Direct:
- Bind to cholinergic receptors to activate them
Indirect:
- Inhibit the enzyme cholinesterase that breaks down ACh in synapse
- Results in more ACh available to activate postsynaptic receptors
How are cholinesterase inhibitors used in skeletal muscles?
For skeletal muscles:
- Causes skeletal muscle contraction
- Used for diagnosis and treatment of myasthenia gravis (autoimmune condition that attacks nicotinic receptors in skeletal muscle neuromuscular junction, includes muscle weakness and drooping eyelids)
- Reverse neuromuscular blocking agents
- Antidote for anticholinergic poisoning
What are the effects of cholinesterase inhibitors?
Makes ACh last longer in the synapse because cholinesterase enzyme is inhibited
When do cholinesterase inhibitors affect muscarinic vs. nicotinic receptors?
Muscarinic receptors are impacted at lower doses
- Mimics actions of PNS
Nicotinic receptors are stimulated at high doses
- Acts in skeletal muscles
What are the adverse effects of cholinesterase inhibitors (SLUDGE)
SLUDGE
Salivation Lacrimation (tears) Urinary incontinence Diarrhea Gastrointestinal cramps Emesis
Also includes pupil constriction, increased intraocular pressure, decreased heart rate, and bronchial constriction/narrowed airways
How are cholinesterase inhibitors used in treating Alzheimer’s?
Alzheimer’s is caused by a loss of cholinergic neurons
- Donepezil (Aricept) is an indirect acting agent
- Helps to increase or maintain memory and learning capabilities
- 3-6 weeks for therapeutic effect
What are 2 direct acting agents (cholinergic agonists) and what do they treat?
- Pilocarpine
- Treats glaucoma by reducing intraocular pressure in eye
- Bethanechol
- Aids bladder emptying
- Muscarinic receptor agonist
- Urination should occur within 60 minutes
What are the adverse effects of cholinergic agonists
Adverse effects are a result of overstimulation of the PNS
Cardio:
- *Bradycardia, hypotension, AV block and cardiac arrest
GI:
- Cramps, increased secretions, nausea, vomiting
Resp:
- Increased secretions and bronchospasms
CNS:
- Cholinergic receptors are also in the brain
- Headache, dizziness, convulsions
Other:
- Sweating, lacrimation, salivation, loss of binocular accommodation, miosis (pupil constriction)
Drug interactions with cholinergic agonists?
Reduced effects of cholinergic agonists:
- Anticholinergics, antihistamines (1st gen)
Additive effects:
- Other cholinergic agents
What is the antidote for cholinergic stimulation?
Atropine (muscarinic receptor antagonist)
When should the physician be notified (symptoms)?
Muscle weakness, abdominal cramps, diarrhea, or difficulty breathing
Where are cholinergic-blocking drugs primarily used?
In the PNS - only considering the blockers of muscarinic receptors
Some uses in CNS
What’s the difference between anticholinergics, cholinergic blockers, and muscarinic antagonists?
They’re all the same for this class!
What’s the function for muscarinic antagonists?
Compete with ACh for binding to muscarinic receptors
- ACh is unable to bind to the receptor site and produce a cholinergic effect
What drugs are natural vs. synthetic? (4)
Natural
- Atropine
- Scopolamine
Synthetic
- Benztropine
- Ipratropium
What are the adverse effects of muscarinic antagonists (larger vs. smaller)?
Cardio
- *Large doses can increase heart rate
- Small doses decrease heart rate
CNS
- Large doses: drowsiness, disorientation, hallucinations
- Smaller doses: mild restlessness, decrease muscle rigidity and tremors
Respiratory
- Decreased bronchial secretions
- Dilated bronchial airways
Eyes
- Dilated pupils (mydriasis)
- Decreased accommodation due to paralysis of ciliary muscles (cycloplegia) can’t focus on close objects
GI
- Decrease smooth muscle tone of GI tract
- Decrease motility and peristalsis
- Decreased secreations
Genitourinary
- Relax detrusor muscle (bladder)
- Urinary retention
Glands
- Decreased bronchial secretions, salivation and sweating
When to use muscarinic antagonists?
Parkinson’s disease
- Reduce muscle rigidity and tremors
- *Benztropine
Respiratory
- Decreased secretions from nose, mouth, pharynx, bronchi
- *Ipratropium used to treat exercise-induced bronchospasms, chronic bronchitis, asthma, COPD
GI
- Decreased secretions and GI motility and peristalsis
- Used to treat peptic ulcer disease, IBS, diarrhea
GU
- Causes relaxed detrusor muscles and increased constriction of the internal sphincter
- Used for reflex neurogenic bladder and incontinence
When do you use the drug Atropine?
For cardiovascular disorders like:
- Cardiac sinus node dysfunction
- Symptomatic second-degree heart block
- Sinus bradycardia (advanced life support)
- *To reduce anesthesia-induced bradycardia
- REduce secretions
What is the antidote for Atropine?
Physostigmine (a cholinesterase inhibitor)
