In the context of asthma, which property is shared by acetylcholinesterase inhibitors, muscarinic agonists such as pilocarpine, and beta-blockers?
|A||Are preferred topical antiglaucoma drugs for patients with asthma|
|B||Contraindicated, or pose great risks, for people with asthma|
|C||Degranulate mast cells, so they cause bronchoconstriction|
|D||Useful for acute asthma, not for ambulatory patients|
a. An important element in the pathophysiology of asthma is airway smooth-muscle hyperresponsiveness to various bronchoconstrictor stimuli, ACh clearly among them.
b. Acetylcholinesterase inhibitors and such muscarinic agonists as pilocarpine are sometimes used as topical miotics for managing glaucoma (mainly angle-closure/narrow angle forms of the disease).
c. Certain topical β blockers are used for open-angle glaucoma, probably working by inhibiting aqueous humor production. However, all these drugs are contraindicated for asthma patients—even if or when they are used topically on the eye(s).
d. ACh esterase inhibitors cause what amounts to a “build-up” of ACh at the neuroeffector junction. These drugs, whether used for glaucoma or such other conditions as myasthenia gravis, can have lethal effects for some asthma patients. (Note, that ACh esterase inhibitors are found in some insecticides, so there is a risk to the asthma patient in agricultural or gardening/lawn care activities.)
e. Muscarinic agonists, whether those used for glaucoma or for stimulating the gut or urinary tract (e.g., bethanechol for functional urinary retention) may prove lethal too. Finally, asthmatics tend to be extremely dependent on the bronchodilator actions of circulating epinephrine. Block the Beta2 receptors that mediate that effect and the outcome can be disastrous.