In Vivo Evaluation Using Gamma Scintigraphy - Pharmaceutical Technology

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In Vivo Evaluation Using Gamma Scintigraphy
The authors discuss gamma scintigraphy as a technique for in vivo evaluation of drugs and delivery systems.


Pharmaceutical Technology


Applications

Gamma scintigraphy can be applied in drug-delivery technologies and advanced pharmacokinetic studies. It also is also useful for evaluating new drugs in the developmental phase, for characterizing new formulations and delivery systems, for establishing bioequivalence of generic products, for monitoring the therapeutic benefits and outcomes of a drug, and for assessing site and organ targeting studies (1). Imaging, pharmacoscintigraphy, and biodistribution are other important applications.

Imaging . Imaging is commonly used to monitor the performance of a drug-delivery systems under normal physiological conditions in a noninvasive manner. The relevance of this process in oral drug delivery includes the assessment of buccal drug delivery, oesophageal transit studies, analysis of gastroretentive dosage forms, gastric-emptying studies, and GI-transit evaluation. Food effects, intra- and inter-subject variability, along with the site of delivery such as the investigation of formulations designed to target the colon, also can be explored with this study. Other possible routes that can be imaged include parenteral, rectal, nasal, pulmonary, and ophthalmic (13–15).

Pharmacoscintigraphy . Pharmacoscintigraphy integrates gamma scintigraphy and pharmacokinetic data to assess the behavior of a dosage form in subjects under investigation. Instead of relying on pharmacokinetic findings alone, it is better to unite these parameters with the technique of gamma scintigraphy to investigate the performance of the dosage form in humans (16). In these studies, the radiolabeled-dosage form is administered to volunteers or patients. Images are acquired using a gamma camera, permitting visualization of the dosage form in the body in a noninvasive manner. A radionuclide tagged with drugs, formulations and devices provides vital information about the rate and extent of drug absorption (17). This technology has the potential to play a role in evaluating various modified-release formulations, for optimizing drug bioavailability, and for understanding the causes of poor absorption (1, 5). Such investigational studies provide ways for evaluating formulations and the drug-delivery system in preclinical and clinical development. The performance of the formulation, which includes the ability of a delivery system to target a specific location, the rate of erosion in comparison with in vitro dissolution data, and the effect of the absorption window on bioavailability, also can be studied using pharmacoscintigraphy (18). Combining the imaging information with the pharmacokinetic data provides functional and valuable knowledge about the release and absorption mechanism of a drug. The imaging techniques can be used to correlate the pharmacology of various molecules, explore pharmacokinetic parameters, and develop proof of concept for drug-delivery systems (1, 2).

Biodistribution. The gamma scintigraphic technique also has been used for biodistribution studies of several drugs radiolabeled with 99mTc. The biodistribution pattern was established for several drugs, including ciprofloxacin, sparfloxacin, and isoniazid (17). Biodistribution also is used in brain targeting, tumor imaging, gene therapy, and bone-targeting delivery systems with the help of SPECT (1, 19–21).

Radiation safety

Although exposure to radioactivity in a large dose can be harmful, the extent of radioactivity from radiopharmaceuticals and related concerns of safety are determined by a nuclear medicine physician. The International Commission on Radiological Protection has established the limits to be followed for use of radiological products (1, 22). These limits are considered to be safe for individuals. The level of radioactivity used in gamma scintigraphy is very low. The dose of radiation administered to participating subjects is well below the maximum permissible dose (5).

Conclusion

Gamma scintigraphy has been successfully used in various scientific fields such as nuclear medicine, pharmaceutical technology, and gastroenterology and can be used for in vivo tracking of drug-delivery systems. Vital information regarding the extent, rate, site, and mode of drug release, along with morphology of drug-delivery systems, in subjects under ethical norms can be obtained using this technique. The authors believe that gamma scintigraphy will continue to be a useful tool in tracking and evaluating drug-delivery systems.

Acknowledgments

The authors would like to acknowledge Kanchan Kohli, associate professor, Department of Pharmaceutics, Hamdard University, New Delhi, India, for providing valuable input for this article.

Rakesh Pahwa* is a faculty member, Himanshu Dutt is a research scholar, and Vipin Kumar and Prabodh Chander Sharma are faculty members at the Institute of Pharmaceutical Sciences, Kurukshetra University, Kurukshetra, India, tel. + 91 9896250793,
.

*To whom all correspondence should be addressed.


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