General

[18F]FDG, a radiolabeled analog of glucose, rapidly distributes, after intravenous injection, to all organs of the body. After background clearance, peak imaging is at 30 - 40 minutes after injection.

Table 3. Physical Decay Chart for Fluorine F 18

Pharmacokinetics

In 4 normal male volunteers, after an intravenous dose given over 30 seconds, the arterial blood level profile for [18F]FDG can be described by a triexponential decay curve. The half-lives for the different distribution and elimination phases are 0.2-0.3 min, 10-13 min (mean ± s.d.; 11.6 ± 1.1 min), and 80-95 min (88 ± 4 min).

Within 33 minutes, a mean of 3.9% of the injected dose can be measured in the urine. Bladder activity two hours after injection indicates that a mean of 20.6% of the injected dose is present. See the Metabolism Section for additional clearance times.

Metabolism

[18F]FDG is taken up by cells and phosphorylated to [18F]FDG-6-phosphate at a rate proportional to the rate of glucose utilization within a given tissue. [18F]FDG-6-phosphate presumably is metabolized to 2-deoxy-2-[18F]fluoro-6-phospho- D -mannose [18F]FDM-6-phosphate).

[18F]FDG contains 2-deoxy-2-chloro- D -glucose (ClDG) as an impurity. Distribution and metabolism of ClDG are presumably similar to that of [18F]FDG, and would be expected to result in intracellular formation of 2-deoxy-2-chloro-6-phospho- D -glucose (ClDG-6-phosphate) and 2-deoxy-2-chloro-6-phospho- D -mannose (ClDM-6-phosphate). The phosphorylated deoxyglucose compounds are dephosphorylated, and the resulting compounds, (FDG, FDM, ClDG and ClDM) presumably leave cells by passive diffusion.

FDG and related compounds are cleared from non-cardiac tissues within 3 to 24 hours after administration; clearance from the heart may require more than 96 hours. [18F]FDG that is not involved in glucose metabolism is excreted unchanged in the urine.

Pharmacodynamics
[18F]FDG is a glucose analogue which concentrates in cells that rely upon glucose as a primary energy source. Once in the cell it is phosphorylated and can not exit until dephosphorylation has occurred. Regions of "increased [18F]FDG uptake" correlate with increased glucose metabolism. Regions of decreased/absent uptake reflect the absence of glucose metabolism. Background activity reflects uptake by normal cells. [18F]FDG uptake in inflammatory cells is inconsistent and may be increased, normal or decreased. Whether or not [18F]FDG, ClDG, or their metabolites can inhibit glucose metabolism is not known.

CLINICAL TRIALS

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