AMD Drugs (Tropicamide and Ranibizumab) Flashcards
What is tropicamide used to do?
Used to dilate the pupils by relaxing the pupillary sphincter. This lets the doctor look at the back of your eye more easily - allowing them to diagnose AMD or other eye conditions - as well as relieving some of the symptoms.
What is the pupillary sphincter?
A circular muscle of the iris and ciliary muscles. It is 1mm wide and consists of smooth muscle fibres.
What does the pupillary sphincter do?
When contracting during bright light, the pupillary sphincter constricts the pupil, which is called miosis. This action happens during accommodation and pupillary light reflexes.
What type of drug is tropicamide?
an alkaloid atropine‐derived anticholinergic drug and is a non-selective muscarinic receptor antagonist
What receptors do tropicamide work on?
muscarinic acetylcholine (mACh) receptors
What are Anticholinergic drugs or alkaloids?
competitive inhibitors of muscarinic receptors.
What is a non-selective antagonist of muscarinic receptors?
Block/inhibit all muscarinic receptors in the body, such as those in the heart, bladder, and intestine, not just those found in the brain. And also works on all subtypes including M1, M2, and M3 receptors.
What do muscarinic receptors do?
when acetylcholine binds to and stimulates these receptors, the muscles and vessels of the eye contract, causing the pupil to get smaller. (so preventing this interaction via antagonist drugs allows the pupil to dilate by blocking this action.)
How long does tropicamide last?
Effects last 4-24hrs
Is tropicamide an agonist or antagonist?
[non-selective] antagonist
What kind of antagonist is tropicamide?
non-selective muscarinic antagonist
What is a parasympathetic antagonist?
drugs that oppose the actions of the PNS at the muscarinic receptors by blocking the actions of acetylcholine. They are also referred to as anticholinergics or parasympatholytics.
What does Acetylcholine do?
Acetylcholine is a neurotransmitter that plays a major role in voluntary and involuntary muscle movement all over your body. It causes nerve cells to stimulate muscle nerve cells, causing muscles to contract.
What part of the eye can the M3 subtype of muscarinic acetylcholine receptors be found in?
The M3 subtype is predominantly expressed by smooth muscle cells of the sphincter pupillae/pupillary sphincter, which is a circular muscle of the iris, and ciliary muscles.
What is the role of M3 receptors in the pupillary sphincter/sphincter pupillae?
In response to light or binding of acetylcholine, M3 receptor signalling leads to contraction of the pupillary sphincter and pupil constriction.
Why is tropicamide a non-selective muscarinic antagonist?
It binds to all subtypes of muscarinic receptors all over the body
How does tropicamide dilate the pupils [FULL]?
By binding to muscarinic receptors, tropicamide relaxes the pupillary sphincter muscle and causes pupil dilation. This is because tropicamide is a antagonist drug, so it inhibits the muscarinic acetylcholine receptors, preventing acetylcholine from binding and stimulating the receptor. This prevents the action of the receptor, meaning the pupillary sphincter muscle cannot contract and constrict the pupil, resulting in the pupil dilating.
In addition, tropicamide dampens the parasympathetic response, so the pupils would not constrict, but would instead dilate as part of the sympathetic response.
What is tropicamide’s effect on the sympathetic responses of the nervous system?
Like other muscarinic antagonists, tropicamide inhibits the parasympathetic drive, allowing the sympathetic nervous system responses to dominate.
In this case, the pupils would not constrict due to the dampened parasympathetic response, but would dilate as part of the sympathetic response.
