The distinctive anatomy and physiognomy of the eye presents obstacles and challenging endeavours to pharmaceutical and research scientists in ophthalmic drug delivery. The currently available formulations suffer with the limitations of increased tear dilution, high tear turnover rate, precorneal elimination leading to high frequency of administration, low drug bioavailability, poor drug permeability. Futhermore, various precorneal (lacrimation, tear production, nasolachrymal drainage) and corneal barriers control the rate and extent of drug permeation. Therapeutic entities can be delivered efficiently to their site of action by the use of penetration enhancers which act by different mechanisms either by altering the properties of the limiting membrane or the therapeutically active drug. The principal focus of the review is to present an insight on the effectiveness of penetration enhancers, their comparative studies, uses and limitations in medications designed for ocular targeting, promoting corneal permeation and eliminating drug loss from the eye.
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