BIODISTRIBUTION AND DOSIMETRY OF INDIUM-111-POLYCLONAL IGG IN NORMAL SUBJECTS

Indium-111-polyclonal IgG is a new imaging agent of infection and infl ammation that has been developed as a possible replacement for radiola beled leukocytes. We undertook a study to determine the safety, biodis tribution and dosimetry of the agent in normal subjects. Methods Twelv e normal male volunteers with an average age of 34 yr (range 21-65 yr) were studied. Each was injected with 1.22-1.47 mCi (111)ln-labeled po lyclonal IgG; digital whole-body images, in addition to blood, urine a nd fecal samples, were obtained immediately after injection and at 6, 24, 48, 72, 96 and 120 hr. Whole-body counts, as well as individual or gan data obtained by outlining regions of interest, were measured. Blo od, urine and fecal counting were done in a well counter and compared to known standards; dosimetry calculations were performed with the MIR D technique. Results: The mean whole-blood activity had a two-phase di sappearance curve: the T1/2I was 11.4 hr (61.1%) and the T1/2II was 11 2.5 hr (38%). Twelve percent of the dose was excreted in the urine and 1.14% in the feces. Skeletal muscle had the highest percentage of upt ake, followed by the bone marrow, liver and lungs; the spleen showed l ess than 1% uptake. Activity in the lungs varied with time, falling by 37% after 18 hr and by 68% after 72 hr. Dosimetry calculations indica ted that the highest absorbed dose was to the liver (1.42 rad/mCi) fol lowed by the testes (1.23 rad/mCi) and red marrow (0.976 rad/mCi). The total-body dose was 0.467 rad/mCi, with an effective dose equivalent of 790.84 mrem. Conclusion: The biodistribution of (111)ln IgG is simi lar to that of Tc-99m-HMPAO-labeled leukocytes. Activity in the liver, kidneys and GI tract may make evaluation of infection in these region s difficult. The dosimetry data indicate that adequate doses can be ad ministered for clinical imaging without exposing the patient to excess ive radiation.