Mohamed Abdel-Rehim, professor of analytical chemistry at Stockholm University in Stockholm, Sweden, spoke to Bethany Degg of The Column about a novel approach to determine drug intake using saliva samples.
Q: What are your main research interests?
A. Saliva is quicker and less invasive to sample from patients than plasma, therefore making it suitable for children and elderly adults. Another important advantage is that there is a lower concentration of proteins in saliva than in plasma, which decreases potential drug binding to proteins. It is widely known that human saliva consists of 99.5% water and the remaining 0.5% consists of electrolytes, glycoproteins, enzymes, and antibacterial compounds. In addition, drugs and their metabolites can be detected at different concentrations within saliva. Our preliminary results indicate that the pharmacokinetic curve of the local anesthetic lidocaine (used as a model analyte) in saliva is similar to those in plasma samples — the only difference is that the concentration levels are lower in saliva than in plasma.1
There have recently been significant developments in the understanding of the target drugs and their pharmacokinetics in oral fluid, but the collection of an exact volume of saliva is not sufficiently accurate. Therefore, the development of new sampling methods for saliva samples is needed.
Q: What novel approach did your group take to sample saliva?
Sometimes saliva can be difficult to work with. This is because saliva stimulated by sympathetic innervation can be thick. We performed our method in two steps: First, we collected saliva using the syringe with a catheter, and then we pushed the saliva through the MEPS needle for the extraction step (Figure 1). Now we are working with a newly developed syringe with two catheter inputs — one for saliva and one for washing and elution solutions — using a wider catheter and a syringe equipped with a micro-valve.
Q: How did you develop MEPS as a sample preparation method for biological samples? What is the story behind it?
A. There is a long history behind the development of MEPS. From 2000–2002, when we were testing solid-phase microextraction (SPME) in bioanalysis, we saw that the robustness of SPME was not good enough for the handling of plasma samples. The most problematic issue of SPME in quantitative bioanalysis is the fibre lifetime. This can drop from 100 extractions to less than 20 depending on the matrix (plasma or blood) and additives used. In addition, the quality of the fibre can differ from batch to batch.2
After a short time I got a lidocaine peak. I was very pleased because it worked the first time and in just a few seconds. When I presented the MEPS to my colleagues, they were astonished that no one had ever thought about it before. The technique provides speed and simplifies the sample preparation process. Later MEPS was patented through AstraZeneca.3 My group and I have performed many experiments with MEPS using different matrices such as water, plasma, urine, blood, and saliva. MEPS has now been automated and we now have MEPS on-line for multiple uses and for single use. Today, many different researchers use the MEPS technique.4