indication

For the topical treatment of chronic open-angle glaucoma.

pharmacology

Demecarium is a long-acting cholinesterase inhibitor and potent miotic. Because of its toxicity, it should be reserved for use in patients with open-angle glaucoma or other chronic glaucomas not satisfactorily controlled with the short-acting miotics and other agents. Application of demecarium to the eye produces intense miosis and ciliary muscle contraction due to inhibition of cholinesterase, allowing acetylcholine to accumulate at sites of cholinergic transmission. These effects are accompanied by increased capillary permeability of the ciliary body and iris, increased permeability of the blood-aqueous barrier, and vasodilation. Myopia may be induced or, if present, may be augmented by the increased refractive power of the lens that results from the accommodative effect of the drug.

mechanism of action

Demecarium is an indirect-acting parasympathomimetic agent, also known as a cholinesterase inhibitor and anticholinesterase. Cholinesterase inhibitors prolong the effect of acetylcholine, which is released at the neuroeffector junction of parasympathetic postganglion nerves, by inactivating the cholinesterases that break it down. Demecarium inactivates both pseudocholinesterase and acetylcholinesterase. In the eye, this causes constriction of the iris sphincter muscle (causing miosis) and the ciliary muscle (affecting the accommodation reflex and causing a spasm of the focus to near vision). The outflow of the aqueous humor is facilitated, which leads to a reduction in intraocular pressure. Of the two actions, the effect on the accommodation reflex is the more transient and generally disappears before termination of the miosis.

toxicity

The oral LD₅₀ is 2.96 mg/kg in the mouse. Symptoms of overdose include nausea, vomiting, abdominal cramps, diarrhea, urinary incontinence, salivation, sweating, difficulty in breathing, bradycardia, or cardiac irregularities.