immunosuppressant drug monitoring: research supports microsampling
Therapeutic drug monitoring (TDM) for immunosuppressive drugs (ISPs) is a critical component of post-tissue and organ transplantation therapy. This is because ISP drugs have high intra- and inter-subject variability and a narrow therapeutic window. Initially, quantitative analyses of ISPs such as sirolimus, cyclosporine A, tacrolimus, and everolimus used whole blood specimens.
Wet samples presented several disadvantages, including a weak correlation with drug concentrations at the place of action and poor prediction of allograft toxicity and survival. Additionally, the methods used to obtain samples were somewhat invasive.
Traditional Sampling Methods for TDM
Alternative blood collection methods have since been developed. The first was the LC-MS/MS method. It allowed researchers to measure drug concentrations in small-sample volumes with adequate selectivity, sensitivity, and robustness.
The main challenge of the LC/MS/MS method is the matrix effect, which produces erroneous results. Clinical researchers suggest cleaning samples and using deuterated IS will mitigate this effect.
Another sampling method for TDM of ISPs has also been introduced, including the use of oral fluids, but it is also bound to produce erroneous results. This is because fluid samples are prone to contamination.
Dried blood spots sampling was the next alternative to traditional whole blood, plasma, and serum TDM. However, research shows ISP concentration on DBS cards and filter paper varies due to the hematocrit effect, among other factors.
A microsampling technique has been developed, and hematocrit effects do not influence it in the same way they do previous outdated dried blood spot technologies such as cards and filter paper. It uses a commercial microsampling device to collect the samples and has proved to collect consistent blood volume independent of hematocrit.
The device has a porous synthetic material which is saturated with biological fluid through capillary action once the tip of the device comes into contact with the fluid. The tip is then dried and removed for the extraction of the analyte.
Microsampling-based TDM allows accurate monitoring of ISP concentrations and offers potential advantages compared to traditional sample collection methods.
Another advantage of microsampling is it offers the possibility of home self-sampling. This feature presents many advantages to bedfast patients and those living in remote areas.
Adequate patient training is necessary for optimum sample collection. Also, proper sample handling and storage after collection is critical to ensure the stability of results.