Summary
Previous studies have shown that radiolabeled tetracyclines tend to accumulate in
infarcts and necrotic tumors. These results suggested that radiolabeled tetracyclines
might also accumulate in necrotic abscesses or areas of inflammation. In order to
develop a better abscess scanning agent, we compared the efficiency of 13II-tetracycline with 67Ga-citrate in labeling experimentally induced staphylococcal aureus abscesses in rats
24 and 72 hours after injection. In addition to evaluating 131I-tetracycline as an abscess scanning agent, we hoped to obtain data which might clarify
the controversy regarding early versus late gallium scanning in suspected infection.
131I-tetracycline was chosen over 99mTc-tetracycline because the longer half-life of 131I would allow 72 hour imaging. Absolute concentrations of gallium in the abscess contents
and in the surrounding areas of inflammation were significantly greater than the concentration
of 131I-tetracycline at both 24 and 72 hours. With the exception of blood, muscle, and bone,
the abscess-to-tissue activity ratios for gallium and 131I-tetracycline were similar; however, the ratio of gallium activity in the inflammed
tissue to other tissues was greater than that of 131I-tetracycline for every tissue
examined at both time periods. The data suggest that 131I-tetracycline has little
potential as a general abscess scanning agent. The gallium tissue concentrations and
tissue ratios suggest that abscesses which can be imaged at 72 hours can probably
be imaged at 24 hours, thus allowing earlier initiation of appropriate therapy. Because
of the higher lesion-toblood ratio at 72 hours, a 72-hour scan would appear to be
indicated before a scan is interpreted as normal.
