The absorption of Tc-99m-alendronate given by rectal route in rabbits

Alendronate sodium (ALD) is a bisphosphonate medication used in the treatment and prevention of osteoporosis. Absorption of ALD as oral formulation is very poor (0.5%-1%). Its bioavailability can decrease with food effect. It has some gastrointestinal adverse effects such as gastritis, gastric ulcer, and esophagitis. The aim of this study was to develop a rectal formulation of ALD as an alternative to oral route and to investigate the absorption of it by using gamma scintigraphy. For this reason, ALD was labeled with Technetium-99m (Tc-99m) by direct method. The radiochemical characterization of the Tc-99m-ALD was carried out by paper chromatography, thin layer chromatography, and electrophoresis methods. The labeling efficiency of Tc-99m-ALD was found 99% without significant changes until 6 h postlabeling at room temperature. The rectal suppositories containing Tc-99m-ALD were prepared by fusion method using polyethylene glycol (PEG) 1500. The Tc-99m-labeled ALD suppositories were administrated to rabbits by rectal route. Serial scintigrams over all bodies of the rabbits were obtained at different time intervals using a gamma camera. We found that the rectal absorption of Tc-99m-ALD from suppository formulation was possible. According to our results, this formulation of ALD can be suggested for the therapy of osteoporosis as an alternative route.