Eye drops are currently the most commonly used dosage form for the treatment of eye diseases, but they will quickly lose from the eye surface, and their drug bioavailability is usually less than 5%. The use of in-situ gel as an ophthalmic drug delivery system can prolong the retention time of drugs in the eyes, reduce the frequency of drug delivery, improve the bioavailability, and achieve the goal of sustained release.

In situ gel is in liquid state in vitro. After administration, the drug will change at the drug site due to temperature, pH value and ionic strength. It will transform from liquid to non chemical crosslinking semisolid gel. In situ gel can be classified as temperature sensitive, pH sensitive and ionic sensitive.

In recent years, the application of ophthalmic gel in ophthalmic drug delivery system has been highly valued by drug researchers. However, due to the specificity of its dosage form, how to effectively study the in vitro release of ophthalmic gel has always been a technical problem.

This article will share the case of using the RT7 Flow-Through Cell Dissolution System to study the in vitro release of ophthalmic gel, hoping to help and inspire you.

Dissolution System: Raytor RT7 Flow-Through Cell Dissolution System

Flow-Through Cell: 22.6mm inner diameter pharmacopoeia standard cell

Test parameters: technical confidentiality

Sampling time point: 5，10，20，30，60，90，120，180，240 min

The following is an in vitro release curve of two different production processes (Sample 1 and Sample 2) of an eye gel, and the average result of parallel test data is obtained from the test results.

The repeatability of the test results is good. The relative standard deviations of the final dissolution rates of Sample 1 and Sample 2 are 0.66% and 0.88% respectively.

In addition, the test results show that the flow-through cell test method and its conditions can distinguish the difference of release degree between different production process batches. We can clearly observe that Sample 2 releases faster than Sample 1.

Ophthalmic in situ gel preparation is liquid at room temperature. After taking medicine, it turns into non chemical crosslinking semisolid gel in the eye, and releases the main ingredient slowly and slowly. Therefore, how to sample the liquid in the in vitro release measurement, how to ensure that the liquid state samples can be completely transformed into semisolid gel, how to make semi-solid gel samples release in a more gentle and more similar environment, and how to reflect the slow release process of samples. These are all considerations for the development of ophthalmic gel in vitro release assay.

With the in-depth and mature research of the flow-through cell, we can study the in vitro release of more and more special durg such as ophthalmic gel formulations. Thanks to the advantages of flow-through cell method, we can get rid of the constraints of traditional dissolution methods and make the determination of in vitro release more meet the expectations of drug developers for the test results.