Paraoxon is an odorless, reddish-yellow oil. Paraoxon is an aryl dialkyl phosphate where both the alkyl groups are ethyl and the aryl group is 4-nitrophenyl. It is a cholinesterase or acetylcholinesterase (AChE) inhibitor. It is an organophosphate oxon, and the active metabolite of the insecticide parathion. Paraoxon is one of the most potent acetylcholinesterase-inhibiting insecticides available, around 70% as potent as the nerve agent sarin, and so is now rarely used as an insecticide due to the risk of poisoning to humans and other animals. Exposure to Paraoxon can cause rapid, severe organophosphate poisoning with headache, sweating, nausea and vomiting, diarrhea, loss of coordination, and death. Paraoxon is on the Hazardous Substance List because it is cited by DOT and EPA. Parathion is converted in the body in part to paraoxon, a strong inhibitor of the enzyme acetyl cholinesterase. Upon inhibition of this enzyme in the tissues, acetylcholine, the substance responsible for transmission of nerve impulses in much of the nervous system, accumulates, producing an initial overstimulation and subsequent blockage of nerve stimuli. Paraoxon was once used as an opthamological drug against glaucoma.

Aceclidine is a parasympathomimetic agent used in the treatment of open-angle glaucoma as topical eye drop solution. It is as a muscarinic acetylcholine receptor agonist with weak anticholinesterase activity. Acting directly on the motor end-plate (cholinergic nerve endings) it decreases intraocular pressure and mediates the contraction of iris muscle. Aceclidine increased outflow facility in human eyes in vitro by a direct stimulation of the outflow tissues in the absence of an intact ciliary muscle. This effect was biphasic, occurring at concentrations of 10 uM and lower with no effect at higher concentrations. Passed numerous clinical trials in Russia, France, Italy and other countries and was widely used in Europe but never been in clinical use in USA.

Befunolol is a beta-adrenergic receptor blocker approved in Japan for the treatment of open-angle glaucoma. The current drug status is unknown.

Tafluprost acid is a prostanoid selective FP receptor agonist that is believed to reduce the intraocular pressure (IOP) by increasing the outflow of aqueous humor. Studies in animals and humans suggest that the main mechanism of action is increased uveoscleral outflow. A prostaglandin analogue ester prodrug used topically (as eye drops) to control the progression of glaucoma and in the management of ocular hypertension. Tafluprost was approved for use in the U.S. on February 10, 2012. Tafluprost, preserved and preservative-free formulations, received marketing approval for the reduction of elevated intraocular pressure (IOP) in open-angle glaucoma and ocular hypertension in several European and Nordic countries as well as Japan, and some other Asia Pacific markets.

Travoprost, an isopropyl ester prodrug, is a synthetic prostaglandin F2 alpha analogue that is rapidly hydrolyzed by esterases in the cornea to its biologically active free acid. The travoporst free acid is potent and highly selective for the FP prostanoid receptor. Travoprost free acid is a selective FP prostanoid receptor agonist and is believed to reduce intraocular pressure by increasing the drainage of aqueous humor, which is done primarily through increased uveoscleral outflow and to a lesser extent, trabecular outflow facility. Travoprost ophthalmic solution is used for the reduction of elevated intraocular pressure in patients with open-angle glaucoma or ocular hypertension who are intolerant of other intraocular pressure lowering medications or insufficiently responsive (failed to achieve target IOP determined after multiple measurements over time) to another intraocular pressure lowering medication. Travoprost is known by the brand names of Travatan and Travatan Z, manufactured by Alcon.

Brinzolamide reduces the amount of fluid in the eye, which decreases pressure inside the eye. Brinzolamide is a carbonic anhydrase inhibitor that is FDA approved for the treatment of elevated intraocular pressure in patients with ocular hypertension or open-angle glaucoma. Common adverse reactions include abnormal taste in mouth and blurred vision. The concomitant administration of brinzolamide and oral carbonic anhydrase inhibitors is not recommended. Plus, in patients treated with oral carbonic anhydrase inhibitors, rare instances of acid-base alterations have occurred with high-dose salicylate therapy.

Latanoprost (free acid) is a metabolite of latanoprost which has been approved for use as an ocular hypotensive drug. Latanoprost is an isopropyl ester prodrug which is converted to the Latanoprost-acid by endogenous esterase enzymes. The free acid is pharmacologically active and is 200 times more potent than latanoprost as an agonist of the human recombinant Prostaglandin F receptor. However, the free Latanoprost-acid is more irritating and less effective than Latanoprost when applied directly to the eyes of human glaucoma patients.

Timolol is the non-selective Beta antagonist used as eye drops to treat increased pressure inside the eye such as in ocular hypertension and glaucoma. Timolol is also used for high blood pressure, chest pain due to insufficient blood flow to the heart, to prevent further complications after a heart attack, and to prevent migraines. Timolol is a beta1 and beta2 (non-selective) adrenergic receptor antagonist that does not have significant intrinsic sympathomimetic, direct myocardial depressant, or local anesthetic (membrane-stabilizing) activity. Timolol, when applied topically on the eye, has the action of reducing elevated, as well as normal intraocular pressure, whether or not accompanied by glaucoma. Elevated intraocular pressure is a major risk factor in the pathogenesis of glaucomatous visual field loss and optic nerve damage. The precise mechanism of the ocular hypotensive action of Timolol is not clearly established at this time. Tonography and fluorophotometry studies of the timolol maleate ophthalmic solution in man suggest that its predominant action may be related to the reduced aqueous formation. However, in some studies, a slight increase in outflow facility was also observed. In a study of plasma drug concentration in six subjects, the systemic exposure to timolol was determined following once daily administration of Timolol Maleate Ophthalmic Gel Forming Solution 0.5% in the morning. The mean peak plasma concentration following this morning dose was 0.28 ng/mL. Side effects, when given in the eye, include burning sensation, eye redness, superficial punctate keratopathy, corneal numbness.

Carbachol is a potent cholinergic (parasympathomimetic) agent which produces constriction of the iris and ciliary body resulting in reduction in intraocular pressure.

Epinephrine is a sympathomimetic catecholamine. It acts as a naturally occurring agonist at both alpha and beta-adrenergic receptors. Three pharmacologic types have been identified: alpha 1-, alpha 2-, and beta-adrenergic receptors. Each of these has three subtypes, characterized by both structural and functional differences. The alpha 2 and beta receptors are coupled negatively and positively, respectively, to adenylyl cyclase via Gi or Gs regulatory proteins, and the alpha 1 receptors modulate phospholipase C via the Go protein. Subtype expression is regulated at the level of the gene, the mRNA, and the protein through various transcriptional and postsynthetic mechanisms. Through its action on alpha-adrenergic receptors, epinephrine lessens the vasodilation and increased vascular permeability that occurs during anaphylaxis, which can lead to loss of intravascular fluid volume and hypotension. Through its action on beta-adrenergic receptors, epinephrine causes bronchial smooth muscle relaxation and helps alleviate bronchospasm, wheezing and dyspnea that may occur during anaphylaxis. Epinephrine also alleviates pruritus, urticaria, and angioedema and may relieve gastrointestinal and genitourinary symptoms associated with anaphylaxis because of its relaxer effects on the smooth muscle of the stomach, intestine, uterus and urinary bladder. Epinephrine increases glycogenolysis, reduces glucose up take by tissues, and inhibits insulin release in the pancreas, resulting in hyperglycemia and increased blood lactic acid.