|A rather unfortunate mistake!|
In the previous instalment I wrote about some common mistakes associated with ‘Specificity’. This time I’ll take a look at ‘Robustness’. The common mistakes that I have selected for discussion are:
1. Investigating robustness during method validation
2. Not investigating the right robustness factors
3. Not doing anything with the robustness results
The purpose of a robustness study is to find out as much as possible about potential issues with a new analytical method and thus how it will perform in routine use. Usually, we deliberately make changes in the method parameters to see if the method can still generate valid data. If it can, it implies that in routine use small variations will not cause problems. This definition is provided in the ICH guideline: “The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage.”
There is another aspect to robustness that doesn’t neatly fit under this definition which applies to the performance of consumable items in the method, such as chromatography columns. The performance of the column when different batches of the same column packing are used may vary. Although column manufacturers aim for batch to batch reproducibility, most practitioners of HPLC will have come across at least one example of this problem. Another issue is the aging of the column, the column performance generally decreases with age and at some stage the column will have to be discarded. Strictly speaking, these column challenges would actually come under the heading of intermediate precision, following the ICH guideline, but it makes much more sense to investigate them during method development as part of robustness.
The method validation guidelines from both ICH and FDA mention the importance of robustness in method development and how it is a method development activity but they do not define whether it needs to be performed under a protocol with predefined acceptance criteria. Since the use of a protocol is a typical approach in most pharma companies it brings me to my first common mistake associated with robustness.
Mistake 1: Investigating robustness during method validation
What I mean by this is that the robustness investigation is performed during the method validation, i.e. the outcome of the investigation is not known. I do not mean the approach where the robustness has already been fully investigated and then it is included as a section in the validation protocol for the sole purpose of generating evidence which can be included in the validation report.
If robustness is investigated during validation for the first time, the risk is that the method may not be robust. Any modifications to improve robustness may invalidate other validation experiments since they are no longer representative of the final method. It will of course depend on what modifications have to be made. As FDA suggests… “During early stages of method development, the robustness of methods should be evaluated because this characteristic can help you decide which method you will submit for approval.”
TIP: If for some reason robustness hasn’t been thoroughly evaluated in method development then investigate it prior to execution of the validation protocol using a specific robustness protocol. If any robustness issues are identified, these can be resolved prior to the validation. The nature of the robustness problems will determine whether the resolution is just a more careful use of words in the written method or if method parameters need to be updated.
Mistake 2: Not investigating the right robustness factors
If you choose the wrong factors you may conclude that the method is robust when it isn’t. Typically what happens then is that there are a lot of unexpected problems when the method is transferred to another laboratory, and since transfer is a very common occurrence in pharma, this can be very expensive to resolve.
When choosing robustness factors it is tempting to read through the method and select all the numerical parameters associated with instrumentation. For example, when assessing HPLC methods there is a tendency to only look at the parameters of the instrument without consideration of the other parts of the method, such as the sample preparation. Unfortunately, sample preparation is an area where robustness problems often occur. Detailed knowledge of how the method works is required to identify the most probable robustness factors.
TIP: The most important factors for robustness are often those which were adjusted in method development. Review all the steps in the method to choose robustness factors and use a subject matter expert to help if necessary.
Mistake 3: Not doing anything with the robustness results
The reason for investigating robustness is to gain knowledge about the method and to ensure that it can be kept under control during routine use. Very often robustness data is presented without any comments in the validation report and is not shared with the analysts using the method. This tick-box approach may be in compliance with regulatory guidance but it is not making the most of the scientific data available. The discussion of the method robustness in the validation report should be a very useful resource when the method needs to be transferred to another laboratory and will assist in the risk assessment for the transfer.
TIP: Review the robustness data thoroughly when it is available and ensure that there is a meaningful discussion of its significance in the validation report.
1. ICH Q2 (R1): Validation of Analytical Procedures: Text and Methodology, 2005, www.ich.org
2. FDA Guidance for Industry: Analytical Procedures and Methods Validation for Drugs and Biologics, 2015, www.fda.gov
In the next instalment, I will write about common validation mistakes for the method performance characteristic of accuracy. If you would like to receive the article direct to your inbox, then sign up for our eNewsletter. You will receive lots of helpful information and you can unsubscribe at any time. We never pass your information on to any third parties.
If you would like to learn more about method validation, and method transfer, then you may be interested in the 3 day course on the topic from Mourne Training Services Ltd. The course has two versions, one applied to small, traditional pharmaceutical molecules and one for large, biological/biotechnology derived molecules. Visit the MTS website for more information.