Imaging of infection and inflammation with 99mTc-Fanolesomab

(99m)Tc-fanolesomab, a murine M class antigranulocyte antibody, is injected directly into patients, avoiding in vitro leukocyte labeling. Normal distribution includes reticuloendothelial system, genitourinary tract, and blood pool. Small bowel activity appears within 4 h, colonic activity by 24 h. Accumulation in infection is via two mechanisms: binding to circulating neutrophils that migrate to the infection and binding to neutrophils and neutrophil debris containing CD-15 receptors already sequestered in the infection. (99m)Tc-fanolesomab is valuable in atypical appendicitis. Its sensitivity, specificity, and accuracy, in 200 patients were 91%, 86%, and 87%, respectively. This agent is comparable to (111)In- labeled leukocytes for diagnosing osteomyelitis in the appendicular skeleton in general and in diabetic patients with pedal ulcers. Preliminary experience suggests (99m)Tc-fanolesomab might replace in vitro labeled leukocytes for other indications as well. Initial clinical investigations found the agent was safe. A transient decrease in circulating leukocytes within 20 min after injection occurred, but with no associated clinical complaints. Recovery averaged about 20 min. One study found no statistically significant HAMA titer elevation and no adverse reactions following injection. In another investigation 5 out of 30 subjects who received two separate antibody injections, exhibited HAMA induction with no serious or severe adverse events. Forty-nine adverse events, including 4 severe ones, were reported among 523 subjects in clinical trials. In 2004, (99m)Tc-falosomab was approved in the United States for use in patients with equivocal presentation of appendicitis. However, following postmarketing reports of serious adverse events, including two fatalities, the agent was withdrawn in late 2005, and its future is uncertain.