As a more advanced dissolution method, the flow-through cell method has better discrimination and in vitro and in vivo correlation than the traditional dissolution method. With better instrument conditions, a suitable dissolution method is also very important.

This research case is to cooperate with a customer to develop and optimize the flow-through cell method for in vitro release determination based on the in vivo pharmacokinetic data of a customer's product under development. The goal is to obtain the in vitro release test results that are related to the in vivo pharmacokinetic data.

Flow-Through Cell Apparatus （USP  Apparatus 4): Raytor RT7 Flow-Through Cell Dissolution System

Preliminary test results - no correlation with in vivo pharmacokinetic data

According to the BE data of self-developed sample 1 and self-developed sample 2, the drug time curve of self-developed sample 1 is located on the Drug Concentration-Time Curve of the reference, and its C max and AUC are significantly higher than those of the reference; The Drug Concentration-Time Curve of self-developed sample 2 is below the drug time curve of the reference preparation, and its C max and AUC are lower than those of the reference preparation.

However, there is no correlation between the preliminary in vitro release test results and in vivo pharmacokinetic data:

(1) The release rate and cumulative dissolution of self-developed sample 2 were slightly higher than that of self-developed sample 1.

(2) The in vitro release results of the reference and self-developed sample 2 are very similar, so it is impossible to effectively distinguish the difference between the two.

In addition, in general, the in vitro release curves of the three samples were similar, and the method discrimination was not ideal.

The preliminary test results are shown in the following figure:

Through in-depth analysis of the in vitro release phenomena, test results and experimental parameters of the samples, we conclude that some experimental parameters of the flow-through cell method limit the real release of the samples. Furthermore, we redesigned the experimental method according to the release principle, dosage form and process characteristics of the sample.

Test results related to in vivo pharmacokinetic data

The in vitro release test results of the redesigned flow-through cell method meet the expected objectives of our experimental design:

The release rate of self-developed sample 1 was faster than that of the reference, and the release rate of self-developed sample 2 was slower than that of the reference. The test results were correlated with the pharmacokinetic data in vivo.

The test results are shown in the following figure:

According to the in vitro release curve, we also found a small regret in the parameters of this method: although it can reflect the difference between the release of self-developed sample 2 and the reference, the difference between them is relatively small.  The difference between self-developed sample 1 and reference is more obvious.

Reviewing the be data of self-developed sample 1 and self-developed sample 2, the difference between the in vivo pharmacokinetics data of self-developed sample 2 and the reference is indeed smaller than that of self-developed sample 1 and the reference. This further confirms that the new method is feasible and worthy of further optimization for better discrimination.

For better discrimination

In order to better distinguish the difference between the in vitro release of self-developed sample 2 and the reference preparation, we readjusted the test parameters, and investigated the influence of key parameters on the test results by controlling variables, such as pH value of dissolution medium, surfactant concentration, flow rate, glass bead filling amount at the bottom of flow-through cell, sample placement position, etc.

After optimization of the above test parameters, the discrimination of in vitro release results is better, and there is still a correlation with in vivo pharmacokinetic data. The test results are shown in the following figure:

After redesigning the original flow-through cell dissolution method and optimizing the key parameters, the in vitro release results were correlated with the in vivo pharmacokinetic data, and the discrimination was good.

This method development was able to meet the expected objectives of the experimental design, but also benefited from the full technical exchange with the client. The key information provided by the client, such as in vivo pharmacokinetic data, sample preparation process, design differences between different self-developed samples, makes the whole process of method development and optimization more targeted, and makes the final in vitro release test method and results have scientific logic and practical significance.

The test results also confirmed once again that the flow-through cell method has the potential to predict the pharmacokinetic characteristics of drug substances, which can greatly boost the research, screening and optimization of preparation process, and make drug research and development more efficient.