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

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 radiopharmaceitticals (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 biodistribittion 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 andlor the (e) alteration of the binding of the radiopharmaceutical on the blood proteins. The effect of drugs on the labeling of blood elements with 99m Tc 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 andlor (v) direct oxidation of the stannous ion. In conclusion, the development of biological models to study the DIR is highly relevant.