Pharmacokinetics Of Radiopharmaceuticals Research Articles

Effects of medicinal plants on radiolabeling and biodistribution of diagnostic radiopharmaceuticals: A systematic review

Radiopharmaceuticals are drugs that contain radioisotopes used for diagnostic and therapeutic purposes. There are evidences that medicinal herbs and their constituents can modify the radiolabeling, biodistribution, and pharmacokinetics of radiopharmaceuticals through drug interaction. To have an overview of the effects and the underlying mechanisms of medicinal plants on the radiolabeling and bioavailability of radiopharmaceuticals, we conducted this study to summarize the current findings in this field. The scientific literature was systematically collected from databases and analyzed. Studies showed that medicinal plants and their constituents can alter radiolabeling and biodistribution via several mechanisms. Interactions with proteins in red blood cells at the same sites, chelating action of stannous and pertechnetate ions, antioxidant action impeding or decreasing stannous ion oxidation, direct oxidation of stannous ions, generation of reactive oxygen species (ROS) which oxidize stannous ions and damage induced in the cell membrane. Most the medicinal plants can decrease the radioactivity of radiopharmaceuticals, but some of them like Peumus boldus, Punica granatum, Nectandra membranacea, Mentha crispa, Rosmarinus officinalis and derivatives such as eugenol and epigallocatechin gallate have increasing effects. In addition, altering feature in some of them is tissue dependent.

Attenuation correction for the large non-human primate brain imaging using microPET

Assessment of the biodistribution and pharmacokinetics of radiopharmaceuticals in vivo is often performed on animal models of human disease prior to their use in humans. The baboon brain is physiologically and neuro-anatomically similar to the human brain and is therefore a suitable model for evaluating novel CNS radioligands. We previously demonstrated the feasibility of performing baboon brain imaging on a dedicated small animal PET scanner provided that the data are accurately corrected for degrading physical effects such as photon attenuation in the body. In this study, we investigated factors affecting the accuracy and reliability of alternative attenuation correction strategies when imaging the brain of a large non-human primate (papio hamadryas) using the microPET Focus 220 animal scanner. For measured attenuation correction, the best bias versus noise performance was achieved using a 57Co transmission point source with a 4% energy window. The optimal energy window for a 68Ge transmission source operating in singles acquisition mode was 20%, independent of the source strength, providing bias-noise performance almost as good as for 57Co. For both transmission sources, doubling the acquisition time had minimal impact on the bias-noise trade-off for corrected emission images, despite observable improvements in reconstructed attenuation values. In a [18F]FDG brain scan of a female baboon, both measured attenuation correction strategies achieved good results and similar SNR, while segmented attenuation correction (based on uncorrected emission images) resulted in appreciable regional bias in deep grey matter structures and the skull. We conclude that measured attenuation correction using a single pass 57Co (4% energy window) or 68Ge (20% window) transmission scan achieves an excellent trade-off between bias and propagation of noise when imaging the large non-human primate brain with a microPET scanner.

A model to evaluate the biological effect of natural products: vincristine action on the biodistribution of radiopharmaceuticals in BALB/c female mice.

Natural products have been widely used by human beings. However, sometimes the biological effects of these products are not fully known. We are trying to develop a model to evaluate the toxicity of compounds employed as therapeutic drugs. This model is based on the capability of natural products to alter the biodistribution of radiopharmaceuticals labelled with technetium-99m (99mTc). The acceptance of 99mTc-labelled radiopharmaceuticals is so rapid and its current use so diverse that it is not possible to study this radionuclide's behaviour in the body more deeply. There is evidence that the biodistribution or the pharmacokinetics of radiopharmaceuticals can be modified by some drugs, by pathological states, by irradiation and by surgical procedures. A lack of knowledge of such factors can induce a misvisualization of the scintigraphic images, leading to a misdiagnosis. Vincristine is a natural product that has been employed in various chemotherapeutic protocols in oncology. We have studied the effect of vincristine on the distribution of [99mTc]methylenediphosphonic acid ([99mTc]MDP) in female mice. After the last dose of vincristine, [99mTc]MDP was injected, the animals were sacrificed and the percentage of radioactivity (%ATI) was determined in the isolated organs. The %ATI was significantly decreased in the uterus, ovary, spleen, thymus, lymph nodes (inguinal and mesentheric), kidney, liver, pancreas, stomach, heart, brain and bone of the animals treated with the natural product. Several biological effects have been reported in patients treated with vincristine. These effects could justify the alterations in the uptake of the radiopharmaceutical in specific organs. Moreover, these results have shown that it is possible to employ this model to evaluate the toxicity of drugs.