What is the pharmacokinetic property of Tc exametazime (HMPAO) related to its brain uptake?

• A. High protein binding
• B. Simple diffusion
• C. Passive transport
• D. Ion exchange

Answer: (B)

The pharmacokinetic property of Tc exametazime (HMPAO) related to its brain uptake being simple diffusion is based on the mechanism by which this radiopharmaceutical crosses the blood-brain barrier. Tc exametazime, when administered, is lipophilic which allows it to diffuse across cell membranes without the need for energy or specific transporter proteins.

This characteristic is essential for its application in brain imaging, as the ability to passively diffuse into the brain facilitates the effective localization of the tracer in brain tissue. Once in the brain, Tc exametazime is converted to a hydrophilic form, which is retained in the tissue, allowing for visualization of brain perfusion during imaging studies.

While high protein binding and passive transport generally describe the transfer of substances in the body, they do not specifically account for the critical role of simple diffusion in the uptake of Tc exametazime across the blood-brain barrier. Ion exchange does not apply here, as it typically describes interactions involving charged particles and is not a mechanism for drug uptake in this context. Therefore, simple diffusion accurately depicts the process by which Tc exametazime enters the brain tissue.