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Everything you need to know about these "soothing agents."
Demulcents are agents that have the ability to form a soothing film over biological tissues such as skin, mucous membranes or the cornea. "Demulcent" comes from the Latin verb "demulcere" which means "to caress." Thus, a demulcent is a "caressing" or soothing agent.
The FDA monograph on ophthalmic drug products for over-the-counter use established a list of ophthalmic demulcents considered safe and effective which included cellulose derivatives (carboxymethylcellulose sodium [CMC], hydroxymethylcellulose, hydroxypropyl methylcellulose [HPMC], methylcellulose), dextran 70, gelatin and liquid polyols (glycerin, polyethylene glycol 300, polyethylene glycol 400, polysorbate 80, propylene glycol, polyvinyl alcohol (PVA) and povidone). These agents are used to alleviate ocular irritation and dryness.
Cellulose derivatives are water-soluble, viscous and transparent. They are virtually nontoxic to living tissues. Gelatin and dextran 70 (a polymer of glucose) are not effective as demulcents alone, but should each be used in combination with another approved demulcent. PVA, a liquid polyol, has long been used as an ophthalmic demulcent and lubricant, as well as a vehicle for ophthalmic drugs. It is less viscous than the cellulose derivatives. The demulcent activity of povidone is similar to that of PVA. Of the other liquid polyols, glycerin, polyethylene glycols and propylene glycol are used as demulcents to soothe and coat the skin and throat. Glycerin and propylene glycol are also used in preparations designed to soothe the cornea.
Uses of Ophthalmic Demulcents
Ophthalmic demulcents are commonly used in artificial tear preparations. The tear film lubricates and moistens the eye. Disruption of the tear film results in dry eye, with the attendant patient discomfort and ocular pathologies. The instillation of artificial tears helps alleviate the symptoms of dry eye, and may serve to decrease corneal damage for patients with dry eye. Recently, ophthalmic demulcents have been introduced into multi-purpose contact lens solutions with the intent to increase lens wear comfort for patients. Complete MoisturePlus (AMO), for example, includes both HPMC and propylene glycol. This article focuses on the properties of ophthalmic demulcents that may be of importance to contact lens wearers.
Hydration
Ophthalmic demulcents have the capacity to bind water. This may increase moisture on the ocular surface, serving to decrease the feeling of dryness experienced by artificial tear...