Scintigraphic assessment of therapeutic aerosols

Drugs are delivered to the upper or lower respiratory tract as aerosols via a range of inhalation devices in order to achieve either topical or systemic effects. It is important to be aware of the deposition pattern within the target organ inasmuch as treatment or prophylaxis will be effective only if sufficient drug is delivered directly to the required site. Drugs delivered to the nasal passages must be retained in the nose sufficiently long enough to exert a local effect or to be absorbed before they are removed by mucociliary clearance. Gamma-scintigraphy is a noninvasive technique capable of giving information about total and regional deposition in the lungs, or deposition in and subsequent clearance from the nasal passages, thus providing data that are difficult or impossible to obtain by other means. Radiolabeling strategies for scintigraphic studies of the respiratory tract usually involve the radionuclide 99mTc, which is added to the formulation in order to trace the location of the drug substance in the body. It is difficult to find suitable gamma ray-emitting radionuclides for direct chemical labeling of drug molecules. Pharmacoscintigraphic studies, combining scintigraphy and conventional pharmacokinetics, are able to give valuable insights into the in vivo behavior of compounds delivered to the systemic circulation via the respiratory tract.