Radionuclide imaging studies in the assessment of nasal drug delivery in humans

An understanding of the deposition and clearance of nasal drug formulations from the human nasal cavity is important in order to optimally exploit the nasal route for delivery of drugs intended for local or systemic applications. Three radionuclide imaging methods may be used to assess nasal drug delivery: (i) gamma scintigraphy; (ii) single photon emission computed tomography (SPECT); and (iii) positron emission tomography (PET). Gamma scintigraphy is used to image the nasal cavity in two dimensions, while SPECT and PET are 3-dimensional imaging methods. By quantifying the deposition and clearance of drug formulations, radionuclide imaging studies allow a comparison to be made between the performance of new nasal drug delivery systems and those already marketed. Imaging data have been used to demonstrate the bioadhesive properties of novel formulations in the nasal cavity and to show that little or no drug usually penetrates directly to the lungs when delivered intranasally. These data may have an important regulatory role by clarifying whether small in vitro differences between products are likely to be clinically significant. Gamma scintigraphy is likely to remain the most widely used radionuclide imaging method, at least for the time being, although a larger future role is likely for SPECT and PET.