Imaging studies of biodistribution and kinetics in drug development

Although the intravenous route of administration is rarely used for drugs, it is by far the most common route for PET and SPECT radiotracers. This article discusses the use of planar and tomographic nuclear medicine technologies to image and quantify the distribution of drugs after local administration. In principle, this would include topical dermatologic, otic, ophthalmic, rectal, and vaginal administration, as well as the intramuscular, oral, and inhalation routes, although precedents do not yet exist for all of these. The studies reviewed focus mainly on oral ingestion and oral and nasal inhalation. The use of nondrug tracers for formulations is discussed, principally with planar imaging or SPECT using radionuclides such as Tc-99m, as well as PET imaging where the active ingredient of a formulation can be labeled with C-11 or sometimes F-18. An example of the latter type is a study of the deposition and kinetics in the lungs and airways of triamcinolone acetonide, an anti inflammatory steroid used for topical treatment of allergic rhinitis and asthma, dispensed from an inhaler. PET has high potential for evaluation of different formulations and delivery devices in the development of topically applied drugs. (C) 2003 Wiley-Liss, Inc.