Quotient Sciences offers comprehensive support for designing and conducting scintigraphic studies, including formulation development, radiolabeling, and data analysis. In this article, we discuss gamma scintigraphy, a non-invasive imaging technique that incorporates a low level of gamma-emitting radionuclide into a drug product that allows drug developers to see the drug's movement within the body.
What is gamma scintigraphy?
Gamma scintigraphy is a non-invasive imaging technique that was first used in the medical industry before transitioning into clinical development. The basic principle involves incorporating a low level of gamma-emitting radionuclide (which emits energy in the form of gamma rays) into a drug product or foods and fluids, which are then administered to healthy volunteers or patients. A gamma camera is then used to detect the gamma rays being emitted, providing detailed information on the deposition, dispersion and movement of the radionuclide within the body. The technique allows visualization and quantification of the dosed radioactivity to better understand what happens to a drug product following administration.
How do drug development teams use gamma scintigraphy?
Scintigraphic studies can be a useful tool in early development to generate data to support marketing claims for products already on the market, or close to being approved. Gamma scintigraphy studies are valuable for proving the concept of new formulations as well as for selecting and optimizing formulations, technologies, or devices. These studies let drug developers also compare products against competitors and to evaluate pharmacodynamic responses, such as mucociliary clearance mechanisms or gastrointestinal motility. Quotient Sciences uses scintigraphy to investigate the performance of different oral solid dosage forms, including inhaled and rectal drug products.
What questions can drug developers answer by using gamma scintigraphy?
Using gamma scintigraphy for oral drug products, some key questions that can be addressed are:
- How long does it take for a dosage form to transit through regions of the gastrointestinal tract?
- How long does drug release take from an oral formulation, and where has this occurred in the gastrointestinal tract?
- What effect does food and gastrointestinal pH have on an orally administered formulation?
- Does the formulation behave in vivo as predicted in vitro?
For inhaled drug products, key questions that using gamma scintigraphy can help answer include:
- Which part of the lungs does the drug reach, and at what quantity?
- How does subject positioning and inhalation technique affect drug delivery to the target region?
- Does the location of drug deposition from an inhaled device change over time?
- Does the administration of the drug improve clearance of mucus from the lungs?
- Has targeted nasal delivery been successful for the administration of systemically acting drugs? (And has any drug reached the sinus or olfactory regions?)
- Can pulmonary deposition be achieved from a nasally administered product?
What data and images are collected using gamma scintigraphy?
Gamma cameras help development teams visualize the gamma-emitting radionuclide within clinical study participants. Following the dosing of the drug product in the clinic, regular images are taken using gamma cameras. The timing and duration of the images are determined on a case-by-case basis for each study, taking into consideration the study design, objectives, and desired outcomes.
For example, if the drug product is an immediate-release dosage form, there will be a high frequency of images taken of the subject for the first 1-2 hours following dosing. For modified release dosage forms, which are intended to release the drug over a long period of time, images could be collected over a 6-12 hour period.
What is pharmacoscintigraphy?
Scintigraphic assessments can be performed with pharmacokinetic (PK) analysis to generate an enhanced understanding of product performance. This is called pharmacoscintigraphy. Pharmacoscintigraphy can be useful in instances where interpretation of the PK data alone can present challenges, or when it is anticipated that the transit and disintegration of an oral formulation may significantly affect the PK data.
Locally-acting drug products can particularly benefit from pharmacoscintigraphy analysis. In these cases, the performance of the dosage form cannot always be assessed accurately by standard PK approaches alone, as the drug concentrations in systemic circulation may not be easily measurable.