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Open Access Highly Accessed Research article

Hydrophilic and lipophilic radiopharmaceuticals as tracers in pharmaceutical development: In vitro In vivo studies

Mariella Terán1*, Eduardo Savio1, Andrea Paolino1 and Malcolm Frier2

Author affiliations

1 Cátedra de Radioquímica – Facultad de Química – Universidad de la República. Montevideo, Uruguay

2 Radiopharmacy Unit. Queen's Medical Centre, Nottingham University. Nottingham, UK

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Citation and License

BMC Nuclear Medicine 2005, 5:5  doi:10.1186/1471-2385-5-5

Published: 18 October 2005

Abstract

Background

Scintigraphic studies have been performed to assess the release, both in vitro and in vivo, of radiotracers from tablet formulations. Four different tracers with differing physicochemical characteristics have been evaluated to assess their suitability as models for drug delivery.

Methods

In-vitro disintegration and dissolution studies have been performed at pH 1, 4 and 7. In-vivo studies have been performed by scintigraphic imaging in healthy volunteers. Two hydrophilic tracers, (99mTc-DTPA) and (99mTc-MDP), and two lipophilic tracers, (99mTc-ECD) and (99mTc-MIBI), were used as drug models.

Results

Dissolution and disintegration profiles, differed depending on the drug model chosen. In vitro dissolution velocity constants indicated a probable retention of the radiotracer in the formulation. In vivo disintegration velocity constants showed important variability for each radiopharmaceutical. Pearson statistical test showed no correlation between in vitro drug release, and in vivo behaviour, for 99mTc-DTPA, 99mTc-ECD and 99mTc-MIBI. High correlation coefficients were found for 99mTc-MDP not only for in vitro dissolution and disintegration studies but also for in vivo scintigraphic studies.

Conclusion

Scintigraphic studies have made a significant contribution to the development of drug delivery systems. It is essential, however, to choose the appropriate radiotracers as models of drug behaviour. This study has demonstrated significant differences in release patterns, depending on the model chosen. It is likely that each formulation would require the development of a specific model, rather than being able to use a generic drug model on the basis of its physicochemical characteristics.