Document Type: Review Article
Department of Medicinal Chemistry, Faculty of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Research Institute for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Gamma-scintigraphy is applied extensively in the development and evaluation of pharmaceutical delivery systems, particularly for monitoring formulations in the gastrointestinal and respiratory tracts. The radiolabelling is generally achieved by the incorporation of an appropriate radionuclide such as technetium-99m or indium-111 into the formulation or by addition of a non-radioactive isotope such as samarium-152 followed by neutron activation of the final product. Drug delivery systems can be tested in vitro using various techniques like dissolution rate. Since in vitro testing methods are not predictive of in vivo results, such systems should be evaluated in vivo using animal models, especially oral dosage forms. Altered gastrointestinal transit due to individual variation, physiologic or pharmacologic factors, or the presence of food may influence bioavailability. Disintegration or drug release may be premature or delayed in vivo. Similarly, altered deposition or clearance from other routes of administration such as nasal, ocular or inhalation may explain drug absorption anomalies. Therefore, there is a growing tendency for new drug delivery systems to be tested, whenever possible, in human subjects, in a so called phase 1 clinical evaluation. Gamma-scintigraphy combined with knowledge of physiologic and dosage form design can help to identify some of these variables. The resulting insight can be used to accelerate the formulation development process and to help to ensure success in early clinical trials.