Direct cholinomimetics work at muscarinic cholinoceptors and thus have similar effects as stimulation of the parasympathethic division of the autonomic nervous system.
Bethanechol is a direct cholinomimetic agent that is structurally similar to acetylcholine, and acts to stimulate bladder contraction, along with gastrointestinal motility.
Bethanechol helps to activate bowel and bladder smooth muscle. It helps to prevent urine retention and ileus by stimulating smooth muscle motor activity.
Methacholine is another parasympathomimetic drug that is used for asthma diagnosis in the methacholine challenge test.
Methacholine can be used for the diagnosis of bronchial hypersensitivity in patients with asthma. Patients whose asthma is less clinically apparent are typically more sensitive to methacholine challenge, compared to normal patients.
Pilocarpine is a strong stimulator of saliva, sweat and tears and can be used to treat both open-angle and closed-angle glaucoma. It may be administered as an ocular insert or as eyedrops.
Pilocarpine's mechanism of action is to contract the ciliary muscle of the eye for open-angle glaucoma and the pupillary sphincter for closed-angle glaucoma. It is resistant to acetylcholinesterase. Patients show miosis after administration.
Carbachol is a cholinomimetic agent similar to acetylcholine and is predominantly used in cases of open-angle glaucoma. Although in some rare cases, it has been used for closed-angle glaucoma.
Carbachol helps in relieving introcular pressure and can be used to cause pupillary contstriction. This helps to treat open-angle glaucoma.
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