Real Life Experiences Using the Wrair Whole Blood and Pyridostigmine Assays

Walter Reed Army Institute of Research Whole Blood (WRAIR WB) cholinesterase assay rapidly determines the concentrations of both AChE and BChE in unprocessed whole blood, uses a minimally invasive blood sampling technique (finger prick), and is fully automated (using the Biomek 2000 robotic system). In human blood from volunteers given pyridostigmine bromide (30 mg single dose), RBC-AChE was maximally inhibited by about 30% after 2.5 h, with recovery to 95% after 24 h. After ex vivo addition of GD to inhibit AChE, and subsequent PB and GD removal, we found that all the protected (by PB pretreatment) AChE activity was recovered after 24h (essentially within 6 h). The same blood samples were evaluated using a WRAIR-developed HPLC method to directly quantify PB. The assay is sensitive to 1 ng.mL with high precision. There was excellent agreement between levels of PB in plasma and AChE inhibition observed. Thus, these assays provide validated support for PB pretreatment as protection against organophosphate chemical warfare agents.