Incurred sample reanalysis: a global transformation

The reproducibility of the reported drug concentration value from an analytical method employed is an important and useful feature in the conduct of quantitative bioanalysis; it is crucial to establishing the reliability of the reported bioanalytical results. While a method might produce acceptable data during the prestudy validation periods, it is critical to demonstrate reproducibility during the in-study phase, when subject/patient biological samples are analyzed for drug concentrations. Therefore incurred sample reanalysis (ISR) is both a fundamental concept and an integral part in the conduct of pharmacokinetic, bioequivalence and preclinical safety studies. Furthermore, the reproducibility demonstrated by ISR reinforces confidence that the method is valid and the results dependable.

ISR is by no means a new phenomenon nor is it only recently being practiced. The Canadian regulatory authorities should be credited for recognizing the issue and its early requirement, approximately 20 years ago. However, this practice had gradually become nonexistent. The continued emphasis on ISR became necessary when, in spite of the demonstration of adequate precision and accuracy during the prestudy validation phase, bioanalytical data submitted to the US FDA suggested that in many cases methods were not reproducible in the actual subject samples (up to 300% difference from original value). Such data from both the FDA and the drug industry were presented in professional meetings and recommendations to perform ISR were made. The current practice for the most part can be summarized as follows and used as a reference in conducting ISR studies:

• ▪ Assess ISR for all bioequivalence studies;

• ▪ For other clinical studies with pharmacokinetic determinations, consider necessary ISR experiments on a case-by-case basis;

• ▪ For preclinical studies, assess ISR once per method/species/laboratory;

• ▪ Maintain and follow standard operating procedures;

• ▪ Sample size equivalence where 10% up to 1000 samples with an additional 5% thereafter; meaningful ISR experiments are representative of study conduct overall;

• ▪ Acceptance criteria equivalence where 67% of repeats agree within 20% for small molecules and 30% for large molecules;

• ▪ Results expressed as percentage difference (i.e., repeated value - original value/average);

• ▪ Failed ISR must lead to an investigation, resolution and documentation;

• ▪ Include ISR results in final report for study.

The above points appear to be the current working procedures and are generally viewed as quite sufficient. Yet, based on further experience, optimization of these issues will be possible. The upcoming FDA revised guidance may provide further information and reference.

The published 2007 White Paper [1], led by the FDA along with industry and professional society participation, demonstrated the collective understanding of the significance of ISR. As it takes a considerable period of time to introduce any official FDA document, the industry started conducting ISR experiments based on the merit of the issue and the overall benefit in the absence of formal guidance. Even so, it must be pointed out that guidance is just that, nonbinding to parties involved. Furthermore, although regulatory oversight is present by virtue of compliance inspections, it constitutes only a small percentage across the vast landscape of bioanalytical laboratories. Indeed, credit should be given to the industry awareness of this significant issue in addressing the reliability of quantitative bioanalysis.

Since the Crystal City conference focused on ISR [2], enormous interest was generated in the area of ISR and the practice of conducting ISR experiments, which not only started in North America but gradually extended to Europe, Asia-Pacific and South America. There were many discussion forums and much data on the subject were shared in international scientific and regulatory meetings. A breadth of literature has appeared in peer-reviewed journals as well. In fact, even without the intervention of regulatory authorities, certain pharmaceutical firms appeared to have chosen to reject studies that lacked reproducibility, pursuing instead different methods and different laboratories. It is also interesting to note that when major issues develop with CROs over multiple applications, a reanalysis for verification appears to be a path for resolution. This option, as an alternate to repeating the whole study or studies, is welcome news and can lead to an effective and less expensive resolution. Thus ISR can be viewed, under these circumstances, as an effective tool for resolution rather than a routine regulatory requirement. Of course, in such cases, a robust ISR program should have been implemented as a part of the original study. Many early nonbelievers in the concept of ISR as well as those who hesitated to adopt, as it creates additional work, now appear to embrace it with ease.

Recently the European Medicines Agency has published its final regulatory guidance that supports the ISR concept and is complimentary to the issues discussed. It is possible that other countries might develop their own guidance in the near future as well. In this context, it is important to note that scientific concepts remain the same from region-to-region, but interpretations and opinions can vary. Thus, the expectations and requirements for the same issue can be different. However, harmonized requirements possess an overall benefit to the regulatory community and provide a common platform for various regulatory authorities. While the industry is quite interested in such harmonization and eventual globalization, robust and sustained efforts are necessary in collaborating and minimizing the differences based on science and practical approach.

Unified requirements that promote a single global standard are highly desirable and can be used as a reference for both regulatory agencies to have oversight in terms of compliance and the regulated industry to follow as a guide. Many firms and laboratories conduct studies and generate data, but often submit the same data to various regulatory authorities. The potential to save time, labor and cost will be immense if we can manage to establish unified standards.

While recognizing the practical aspects of a regulated environment, credit should be extended to drug-industry personnel for a nearly seamless incorporation of ISR in their work and the spontaneity of its practice based on the significance of this issue. This certainly is a welcome example for the future of globalization issues in drug development.