Source: FDA, National Drug Code (US) Revision Year: 2020
F18 Fludeoxyglucose is a glucose analog that concentrates in cells that rely upon glucose as an energy source, or in cells whose dependence on glucose increases under pathophysiological conditions. Fludeoxyglucose F18 is transported through the cell membrane by facilitative glucose transporter proteins and is phosphorylated within the cell to [F18]-FDG-6-phosphate by the enzyme hexokinase. Once phosphorylated it cannot exit until it is dephosphorylated by glucose-6-phosphatase. Therefore, within a given tissue or pathophysiological process, the retention and clearance of Fludeoxyglucose F18 reflect a balance involving glucose transporter, hexokinase and glucose-6-phosphatase activities. Fludeoxyglucose F18 is used to assess glucose metabolism.
In comparison to background activity of the specific organ or tissue type, regions of decreased or absent uptake of Fludeoxyglucose F18 reflect the decrease or absence of glucose metabolism. Regions of increased uptake of Fludeoxyglucose F18 reflect greater than normal rates of glucose metabolism.
Fludeoxyglucose F18 Injection is rapidly distributed to all organs of the body after intravenous administration. After background clearance of Fludeoxyglucose F18 Injection, optimal PET imaging is generally achieved between 30 to 40 minutes after administration.
In cancer, the cells are generally characterized by enhanced glucose metabolism partially due to (1) an increase in activity of glucose transporters, (2) an increased rate of phosphorylation activity, (3) a reduction of phosphatase activity or, (4) a dynamic alteration in the balance among all these processes. However, glucose metabolism of cancer as reflected by Fludeoxyglucose F18 accumulation shows considerable variability. Depending on tumor type, stage, and location, Fludeoxyglucose F18 accumulation may be increased, normal, or decreased. Also, inflammatory cells can have the same variability of uptake of Fludeoxyglucose F18.
In the heart, under normal aerobic conditions, the myocardium meets the bulk of its energy requirements by oxidizing free fatty acids. Most of the exogenous glucose taken up by the myocyte is converted into glycogen. However, under ischemic conditions, the oxidation of free fatty acids decreases, exogenous glucose becomes the preferred myocardial substrate, glycolysis is stimulated, and glucose taken up by the myocyte is metabolized immediately instead of being converted into glycogen. Under these conditions, phosphorylated Fludeoxyglucose F18 accumulates in the myocyte and can be detected with PET imaging.
In the brain, cells normally rely on aerobic metabolism. In epilepsy, the glucose metabolism varies. Generally, during a seizure, glucose metabolism increases. Interictally, the seizure focus tends to be hypometabolic.
In four healthy male volunteers, receiving an intravenous administration of 30 seconds in duration, the arterial blood level profile for Fludeoxyglucose F18 decayed triexponentially. The effective half-life ranges of the three phases were 0.2-0.3 minutes, 10-13 minutes with a mean and standard deviation (STD) of 12 ± (1) min, and 80-95 minutes with a mean and STD of 88 ± (4) min.
Plasma protein binding of Fludeoxyglucose F18 has not been studied.
Fludeoxyglucose F18 is transported into cells and phosphorylated to [F18]-FDG-6-phosphate at a rate proportional to the rate of glucose utilization within that tissue. [F18]-FDG-6-phosphate presumably is metabolized to 2-deoxy-2-[F18]fluoro-6-phospho-D-mannose([F18]FDM-6-phosphate).
Fludeoxyglucose F18 Injection USP may contain several impurities (e.g., 2-deoxy-2-chloro-D-glucose (ClDG)). Biodistribution and metabolism of ClDG are presumed to be similar to Fludeoxyglucose F18 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. Fludeoxyglucose F18 and related compounds are cleared from non-cardiac tissues within 3 to 24 hours after administration. Clearance from the cardiac tissue may require more than 96 hours. Fludeoxyglucose F18 that is not involved in glucose metabolism in any tissue is then excreted in the urine.
Fludeoxyglucose F18 is cleared from most tissues within 24 hours and can be eliminated from the body unchanged in the urine. Within 33 minutes, a mean of 3.9% of the administrated radioactive dose was measured in the urine. The amount of radiation exposure of the urinary bladder at two hours post-administration suggests that 20.6% (mean) of the radioactive dose was present in the bladder.
The pharmacokinetics of Fludeoxyglucose F18 Injection have not been studied in renally-impaired, hepatically impaired or pediatric patients. Fludeoxyglucose F18 is eliminated through the renal system. Avoid excessive radiation exposure to this organ system and adjacent tissues.
The effects of fasting, varying blood sugar levels, conditions of glucose intolerance, and diabetes mellitus on Fludeoxyglucose F18 distribution in humans have not been ascertained [see Warnings and Precautions (5.2)].
Animal studies have not been performed to evaluate the Fludeoxyglucose F18 Injection carcinogenic potential, mutagenic potential or effects on fertility.
The efficacy of Fludeoxyglucose F18 Injection USP in positron emission tomography cancer imaging was demonstrated in 16 independent studies. These studies prospectively evaluated the use of Fludeoxyglucose F18 in patients with suspected or known malignancies, including non-small cell lung cancer, colo-rectal, pancreatic, breast, thyroid, melanoma, Hodgkin’s and non-Hodgkin’s lymphoma, and various types of metastatic cancers to lung, liver, bone, and axillary nodes. All these studies had at least 50 patients and used pathology as a standard of truth. The Fludeoxyglucose F18 Injection doses in the studies ranged from 200 MBq to 740 MBq with a median and mean dose of 370 MBq.
In the studies, the diagnostic performance of Fludeoxyglucose F18 Injection varied with the type of cancer, size of cancer, and other clinical conditions. False negative and false positive scans were observed. Negative Fludeoxyglucose F18 Injection PET scans do not exclude the diagnosis of cancer. Positive Fludeoxyglucose F18 Injection PET scans cannot replace pathology to establish a diagnosis of cancer. Non-malignant conditions such as fungal infections, inflammatory processes and benign tumors have patterns of increased glucose metabolism that may give rise to false-positive scans. The efficacy of Fludeoxyglucose F18 Injection PET imaging in cancer screening was not studied.
The efficacy of Fludeoxyglucose F18 Injection for cardiac use was demonstrated in ten independent, prospective studies of patients with coronary artery disease and chronic left ventricular systolic dysfunction who were scheduled to undergo coronary revascularization. Before revascularization, patients underwent PET imaging with Fludeoxyglucose F18 Injection (74–370 MBq, 2–10 mCi) and perfusion imaging with other diagnostic radiopharmaceuticals. Doses of Fludeoxyglucose F18 Injection ranged from 74-370 MBq (2-10 mCi). Segmental, left ventricular, wall-motion assessments of asynergic areas made before revascularization were compared in a blinded manner to assessments made after successful revascularization to identify myocardial segments with functional recovery.
Left ventricular myocardial segments were predicted to have reversible loss of systolic function if they showed Fludeoxyglucose F18 accumulation and reduced perfusion (i.e., flow-metabolism mismatch). Conversely, myocardial segments were predicted to have irreversible loss of systolic function if they showed reductions in both Fludeoxyglucose F18 accumulation and perfusion (i.e., matched defects).
Findings of flow-metabolism mismatch in a myocardial segment may suggest that successful revascularization will restore myocardial function in that segment. However, false-positive tests occur regularly, and the decision to have a patient undergo revascularization should not be based on PET findings alone. Similarly, findings of a matched defect in a myocardial segment may suggest that myocardial function will not recover in that segment, even if it is successfully revascularized. However, false-negative tests occur regularly, and the decision to recommend against coronary revascularization, or to recommend a cardiac transplant, should not be based on PET findings alone. The reversibility of segmental dysfunction as predicted with Fludeoxyglucose F18 PET imaging depends on successful coronary revascularization. Therefore, in patients with a low likelihood of successful revascularization, the diagnostic usefulness of PET imaging with Fludeoxyglucose F18 Injection is more limited.
In a prospective, open label trial, Fludeoxyglucose F18 Injection was evaluated in 86 patients with epilepsy. Each patient received a dose of Fludeoxyglucose F18 Injection in the range oF185-370 MBq (5-10 mCi). The mean age was 16.4 years (range: 4 months – 58 years; of these, 42 patients were less than 12 years and 16 patients were less than 2 years old). Patients had a known diagnosis of complex partial epilepsy and were under evaluation for surgical treatment of their seizure disorder. Seizure foci had been previously identified on ictal EEGs and sphenoidal EEGs. Fludeoxyglucose F18 Injection PET imaging confirmed previous diagnostic findings in 16% (14/87) of the patients; in 34% (30/87) of the patients, Fludeoxyglucose F18 Injection PET images provided new findings. In 32% (27/87), imaging with Fludeoxyglucose F18 Injection was inconclusive. The impact of these imaging findings on clinical outcomes is not known.
Several other studies comparing imaging with Fludeoxyglucose F18 Injection results to subsphenoidal EEG, MRI and/or surgical findings supported the concept that the degree of hypometabolism corresponds to areas of confirmed epileptogenic foci. The safety and effectiveness of Fludeoxyglucose F18 Injection to distinguish idiopathic epileptogenic foci from tumors or other brain lesions that may cause seizures have not been established.
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