Microsampling in in vivo PK studies
5 July 2018
Microsampling technology in drug discovery and development has been gaining a serious foothold within the industry over the last decade. We at Admescope have been providing microsampling as a part of our in vivo PK services for well over a year now and this feels like a good time to let Dr Janne Mannila, our Head of In vivo PK studies share his experiences with microsampling over an interview.
What is microsampling?
While the term microsampling refers to collection of less than 50µl samples of blood from test subjects, modern microsampling techniques enable accurate sampling of volumes that are significantly lower, even as low as 5 – 10 µl volumes. Since the invention of the original microsampling method, the dried blood spot sampling (DBS), alternative technologies for microsampling have become available. Most notable of these newer technologies are capillary microsampling (CMS) and volumetric absorptive microsampling (VAMS).
Which microsampling method do you utilise in in vivo studies?
We use the Mitra® microsampling system which is based on the VAMS technology. The Mitra device is used to collect exactly 10µl of blood from a small prick to the test animal’s skin, e.g. cheek or tail by capturing the sample in the absorbent tip of the device. The sample is then placed in a plastic protective case to dry in room temperature. After drying, the sample is eluted from the absorbent with organic solvent for analysis with LC/MS.
What are the pros when using Mitra?
Mitra is very handy when taking samples from rodents and especially with mice as you can take up to 6-8 blood samples from the same mouse over the 24-hour period in a basic PK study. With the traditional sampling method, you can only take 1-2 samples from a single mouse in such a study and you would have to use 3-4 animals to get all the endpoints for the PK profile which leaves room for error on the basis of physiological variation between individual animals. This can be avoided by using microsampling. Also, with microsampling you can greatly reduce the number of test animals needed for a single study leading to reduced costs and of course better adherence to the 3R principle. In addition, our lab technicians really like using Mitra for sampling as it is very easy to use. The samples don’t require freezing and even the preparation for LC-MS analysis is straightforward.
And the cons?
The biggest disadvantage of Mitra is that the analysis of the samples provides whole blood kinetics as quite often we are interested in plasma kinetics. Fortunately, we can calculate the plasma kinetics from Mitra samples with the help of blood-to-plasma ratio of the compound. This, of course requires performing an additional assay to measure the blood-to-plasma ratio if not known beforehand. It is also possible that the reduced sample volume can create challenges in bioanalysis near the limit of quantitation, but this can be taken into account with prior planning, e.g. by slightly adjusting the sampling regimen. It should be noted that these issues are becoming increasingly rare with the use of modern high-sensitivity MS instruments.
How do you see the future for microsampling in drug discovery & development?
Thanks to the advances in bioanalytical techniques, we no longer require big sample volumes for accurate quantitation and dealing with small volumes is faster and cheaper. Microsampling has also ethical advantages over the traditional sampling as it is less stressful for the animal and reduces the number of required animals for a study. In light of these facts, I would say that microsampling will undoubtedly become more popular over time.
Written by Jouni Jukka & Janne Mannila
PS. For your convenience, I thought to share a link to one of our ebooks for a more comprehensive view on in vivo pharmacokinetics.