Drug interaction with radiopharmaceuticals: effect on the labeling of red blood cells with technetium-99m and on the bioavailability of radiopharmaceuticals

Abstract

The evidence that natural and synthetic drugs can affect radiolabeling or bioavailability of radiopharmaceuticals in setting of nuclear medicine clinic is already known. However, this drug interaction with radiopharmaceuticals (DIR) is not completely understood. Several authors have described the effect of drugs on the labeling of blood elements with technetium-99m (99mTc) and on the biodistribution of radiopharmaceuticals. When the DIR is known, if desirable or undesirable, the natural consequence is a correct diagnosis. However, when it is unknown, it is undesirable and the consequences are the possibility of misdiagnosis and/or the repetition of the examination with an increase of radiation dose to the patient. The possible explanation to the appearance of DIR are (a) radiopharmaceutical modification, (b) alteration of the labeling efficiency of the radiopharmaceutical, (c) modification of the target, (d) modification of no target and/or the (e) alteration of the binding of the radiopharmaceutical on the blood proteins. The effect of drugs on the labeling of blood elements with 99mTc might be explained by (i) a direct inhibition (chelating action) of the stannous and pertechnetate ions, (ii) damage induced in the plasma membrane, (iii) competition of the cited ions for the same binding sites, (iv) possible generation of reactive oxygen species that could oxidize the stannous ion and/or (v) direct oxidation of the stannous ion. In conclusion, the development of biological models to study the DIR is highly relevant.

Uncaria tomentosa extract: evaluation of effects on the in vitro and in vivo labeling of blood constituents with technetium-99m

“…Thus, it is important to develop models that can describe the possible in vitro and in vivo drug interactions. Some authors have described that synthetic or natural products, can alter the labeling of blood constituents with Tc-99m (Braga et al, 2000;Gomes et al, 2002;Bernardo-Filho et al, 2005;Neves et al, 2007). Moreno et al, (2004), have evaluated the effect of a Ginkgo biloba extract on labeling of blood constituents with Tc-99m using in vitro and in vivo study: a reduction of radiolabeling of blood cells was observed with the in vitro method (Moreno et al, 2004).…”

Effect of oral ingestion of an extract of the herb Uncaria tomentosa on the biodistribution of sodium pertechnetate in rats

“…Radiopharmaceuticals (radiobiocomplexes) (6) are radioactive tracers employed in nuclear medicine for the study of several morphological and physiological conditions, such as blood flow and absorption, biodistribution, and metabolism in target and nontarget organs (7).…”

“…Many natural and synthetic products have been reported to affect the biodistribution of different radiobiocomplexes (6)(7)(8)(9). The incorporation of a radionuclide into a drug formulation permits the determination of the biodistribution kinetics and the release sites of the latter (10,11).…”

“…When the drug interaction with radiobiocomplexes is unknown, the examination is not recommended, since the consequences of the procedure are the possibility of misdiagnosis and/or repetition of the examination, with an increase in the radiation dose administered to the patient (7,13). When the drug interaction with radiobiocomplexes is known, whether desirable or undesirable, the natural consequence is a correct diagnosis (7).…”

“…When the drug interaction with radiobiocomplexes is known, whether desirable or undesirable, the natural consequence is a correct diagnosis (7).…”