Biodistribution and radiation dosimetry of [N-methyl-11C]mirtazapine, an antidepressant affecting adrenoceptors

Central adrenoceptors cannot currently be studied by PET neuroimaging due to a lack of appropriate radioligands. The fast-acting antidepressant drug mirtazapine, radiolabelled for PET, may be of value for assessing central adrenoceptors, provided that the radiation dosimetry of the radioligand is acceptable. To obtain that information, serial whole-body images were made for up to 70 min following intravenous injection of 326 and 185 MBq [N-methyl-11C]mirtazapine (specific activities E.O.S. of 119 and 39 GBq/μmol, respectively) in a healthy volunteer. Ten source organs plus remaining body were considered in estimating absorbed radiation doses calculated using MIRD 3.1. The highest absorbed organ doses were found to the lungs (3.4×10−2 mGy/MBq), adrenals (1.2×10−2 mGy/MBq), spleen (1.2×10−2 mGy/MBq), and gallbladder wall (1.1×10−2 mGy/MBq). The effective dose was estimated to be 6.8×10−3 mSv/MBq, which is similar to that produced by several radioligands used routinely for neuroimaging.