Novel Topical Drug Delivery Systems in Ophthalmic Applications

*Ankita Rajput, Palvi Sharma, Ritika Sharma and Shubham Thakur*

### **Abstract**

The eye is the utmost attention-grabbing organ owed to its drug disposition characteristics. Generally, topical application (90% are eye drops) is the method of choice because of its patient compliance and safety. Transcorneal penetration is the major route for ophthalmic drug absorption. However, corneal absorption has been observed to be slower process as compared to elimination. Therefore, conventional dosage forms are associated with rapid precorneal drug loss. Thus, to improve ocular drug bioavailability, there is a substantial effort directed toward the development of novel topical drug delivery systems for ophthalmic administration. These novel delivery systems (Contact lenses, *In situ* gels, Microemulsions, Niosomes, Liposomes, Implants, Microspheres, and Micelles) provide the controlled release behaviour for treating the chronic ailments, and help patients and doctors to curtail the dosing frequency and invasive method of treatment. Hence, the current chapter discusses the progress of novel topical ocular drug delivery systems in the pharmaceutical industry.

**Keywords:** ophthalmic, topical delivery, contact lenses, *In situ* gels, microemulsions, niosomes, liposomes, implants, microspheres, micelles

### **1. Introduction**

Eye is the utmost attention-grabbing organ owed by its drug disposition characteristics. Drug delivery to the eye is hampered by the physiological barricades such as blinking & wash out by tears, nasolacrimal drainage, nonproductive losses, and impermeability of the cornea [1, 2]. Although its easy to administer the drug to eyes but there are various barriers to drug delivery, viz. tear mechanisms, membranes, and blood–aqueous and blood–retinal barriers [3]. The three main routes for administering ophthalmic medication are topical, systemic, and intraocular; each has its own set of benefits and drawbacks.

Topical application (90 percent of which are eye drops) is the preferred method due to patient compliance and safety. The most common route for ophthalmic drug absorption is through transcorneal penetration. Corneal absorption, on the other hand, is a much slower process than elimination. Despite the benefits of ocular

formulations (ease of formulation, storage limitations, and drug instillation), they have several drawbacks, including limited drug accumulation for lipophilic agents, precorneal losses, and the cornea's barrier [4]. As a result, traditional ocular dosage forms have been linked to rapid precorneal drug loss. Effective systemic delivery, can be achieved if high drug concentration circulates in the blood plasma. Furthermore, sustained release of oral drugs may be appropriate for glaucoma patients, allowing for continuous and effective treatment; butin this method the entire body is exposed to the drug, so, side effects can be observed [5]. Moreover, intravitreal drug delivery is an invasive procedure that carries some risk, such as retinal haemorrhage or detachment, especially if the technique is repeated multiple times for treating chronic disorders.

Traditional eye drops are convenient and easy method, but they are ineffective, and only a small portion of the dose is delivered to the target area; the majority is lost owing toclearance mechanisms. As a result, there are significant strategies aimed at developing novel topical drug delivery systems for ophthalmic administration in order to improve ocular drug bioavailability. Solubility enhancers are primarily used to increase the drug concentrations within the formulation; medication in the dosage form enhances the bioavailability. This strategy may allow for the application of a smaller droplet, and loss due to the reflex tearing and blinking can be prevented to larger extent [5]. Second, the formulation can be designed to withstand clearance; these dosage forms are retained for longer periods of time, giving them more time to remain accumulated within the ocular tissue. Finally, drug penetration enhancers can be added to the formulation to help the drug get through the cornea [6]. All of these approaches are novel drug delivery technologies that allow drugs to reach the posterior chamber. These delivery systems viz. contact lenses, *in situ* gels, microemulsions, niosomes, liposomes, implants, microspheres, and micelles provide controlled release for the treatment of chronic eye disorders, reducing dose frequency and invasive treatment.

Following that, the chapter looks at how novel topical ocular drug delivery systems are progressing in the pharmaceutical industry. Future research is likely to lead to the discovery of polymers that outperform those currently in use, such as smart drug delivery systems that release their payload in response to a specific stimulus. Furthermore, a reassess of recent advances in ophthalmic drug delivery necessitates and aids drug delivery scientists in modulating their thought processes and developing novel and safe drug delivery techniques. Its goal is to sumup the existing traditional ocular delivery formulations and their advancements, as well as current developments. In addition, recent advancements in novel ocular drug delivery strategies, such as contact lenses, *in situ* gels, microemulsions, niosomes, liposomes, implants, microspheres, and micelles have been thoroughly discussed.
