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Biodistribution, Radiation Dosimetry and Pharmacokinetics of ¹¹¹In-Antimyosin in Idiopathic Inflammatory Myopathies

Department of Radiology, Great Ormond St. Hospital for Children NHS Trust, London
Department of Cardiology, Northwick Park Hospital, Harrow, Middlesex
Department of Rheumatology, Southend Hospital, Westcliffe-on-Sea, Essex, England

Correspondence: For correspondence or reprints contact: Terry Smith, PhD, Department of Radiology, Great Ormond St. Hospital for Children NHS Trust, Great Ormond St., London WC1N 3JH, UK.

ABSTRACT

In view of the established role of ¹¹¹In-antimyosin in the detection of heart 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 ¹¹¹In-antimyosin in localized sites of skeletal muscle involvement in patients with idiopathic inflammatory myopathies. Methods: After intravenous administration of 74 MBq (2 mCi) ¹¹¹In-antimyosin, gamma camera scintigraphy was performed in 12 adult patients with inflammatory muscle disease and in 2 control patients. Six whole-body scans were performed over 72 h, and uptake of ¹¹¹In-antimyosin in organs was quantified using an attenuation-corrected conjugate counting method. Residence times in source organs were used with MIRDOSE software to obtain radiation dose estimates. Pharmacokinetic parameters were derived from serial whole-blood and plasma ¹¹¹In concentrations. Results: The tracer cleared slowly from the circulation, and highest organ uptakes were found in the marrow and liver; kidneys showed the highest concentrations. Uptake was also evident in spleen, the facial image and male genitalia. Conclusion: For a typical administered activity of 74 MBq ¹¹¹In-antimyosin, the kidneys receive the highest dose (58 mSv), and the effective dose is 11 mSv. Radioactivity was cleared from plasma at an average rate of 136 mL/h, and the mean steady-state distribution was approximately 5 L plasma.

Key Words: ¹¹¹In-antimyosin • idiopathic inflammatory myopathies • internal dosimetry • effective dose • pharmacokinetics