Source: FDA, National Drug Code (US) Revision Year: 2020
When technetium Tc 99m pertechnetate is added to exametazime in the presence of stannous reductant, a lipophilic technetium Tc 99m complex is formed. This lipophilic complex is the active moiety. The lipophilic technetium Tc 99m exametazime complex is taken up and retained in leukocytes.
The relationship between technetium Tc 99m exametazime labeled WBC concentrations and successful imaging was not explored in clinical trials. GI activity is typically not seen through the initial four (4) hours post-injection. By four (4) hours, the hepatobiliary excretion of the Tc 99m exametazime allows tracer (Tc 99m) accumulation in the hepatobiliary system and, hence bowel activity.
During the first hour following the injection, radioactivity is seen in the lungs, liver, gall bladder, spleen, blood pool, bone marrow, kidneys, and bladder. Over the first 1-6 hours, the Tc 99m is visualized in the bowel. At 24 hours post-injection substantial colonic activity is seen. The normal areas visualized in earlier scans are still visible.
Tc 99m excretion occurs via urine and feces.
Two clinical trials of technetium Tc 99m exametazime were performed in a total of 88 patients who had suspected intra-abdominal infection or inflammation. Subjects received both Tc 99m labeled leukocytes and a radiolabeled comparator. Images were obtained at 2 and 30 minutes and at 2, 4 and 24 hours. In two other clinical trials, a total of 127 patients with suspected abdominal inflammation or infection received Tc 99m labeled leukocytes. Imaging was at 24 hours in one study and at 1, 3 and 24 hours in the other. In all four studies images were blindly evaluated and the findings were confirmed by surgery, biopsy or other clinical data.
Based on the above 4 studies, between 2 to 4 hours Tc 99m labeled leukocytes had 95-100% sensitivity and 62-85% specificity. In all studies the false positive and false negatives relate to the bowel background, the location of the site of infection/inflammation and whether or not it is contiguous with the bowel. Images obtained at 24 hours can be unreliable because of a high bowel background.
The interpretation of the images could also be affected by the presence of tumors, infarction and peritonitis [See Warning and Precautions (5.2)]. Liver abscess may be missed in planar imaging because of the bowel background.
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