Biodistribution, radiation dosimetry and pharmacokinetics of In-111-antimyosin in idiopathic inflammatory myopathies

In view of the established role of In-111-antimyosin in the detection of he art muscle pathology, radiation dose estimates were made for this substance . Biodistribution and biokinetic data were obtained from our studies, which failed to show abnormal uptake of In-111-antimyosin in localized sites of skeletal muscle involvement in patients with idiopathic inflammatory myopat hies. Methods: After intravenous administration of 74 MBq (2 mCi) In-111-an timyosin, gamma camera scintigraphy was performed in 12 adult patients with inflammatory muscle disease and in 2 control patients. Six whole-body scan s were performed over 72 h, and uptake of In-111-antimyosin in organs was q uantified using an attenuation-corrected conjugate counting method. Residen ce times in source organs were used with MIRDOSE software to obtain radiati on dose estimates. Pharmacokinetic parameters were derived from serial whol e-blood and plasma In-111 concentrations. Results: The tracer cleared slowl y from the circulation, and highest organ uptakes were found in the marrow and liver; kidneys showed the highest concentrations. Uptake was also evide nt in spleen, the facial image and male genitalia. Conclusion: For a typica l administered activity of 74 MBq In-111-antimyosin, the kidneys receive th e highest dose (58 mSv), and the effective dose is 11 mSv. Radioactivity wa s cleared from plasma at an average rate of 136 mL/h, and the mean steady-s tate distribution was approximately 5 L plasma.