**2. Classification of radiopharmaceuticals**

In general, four types of radiopharmaceuticals are used in medical practice. The first of these is ready to use radiopharmaceuticals. These products have a shelf life. Administration to the patient is performed after the radioactive decay is calculated. Iodine (I-123) capsules, I-131 hippurane, Gallium (Ga-67) citrate, Tallium (Tl-201) chloride, Xsenone (Xe-133) aerosol, Technetium (Tc-99 m) pertechnetate are the examples of this group. The second type of radiopharmaceuticals is radiopharmaceuticals obtained from semi-manufactured products. They are prepared by combining the kits with radionuclides that obtained from the generator. The third type of radiopharmaceuticals is prepared directly before use. Products of this group should be prepared and used immediately. Examples of this group are the particle accelerator products. The fourth type of radiopharmaceuticals is based on preparation of samples taken from the patient. The patient's cell or plasma proteins are radiolabeled with radionuclide and given to the same patient. An example of this group is Tc-99 m radiolabelled WBC. The laboratories have different regulations and rules because of this, radiolabelling efficiency and cell viability should be checked for this group after radiolabeling process [5].

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*Computational Study of Radiopharmaceuticals DOI: http://dx.doi.org/10.5772/intechopen.85140*

**3. Computational models for drug development**

effective molecules could be designed by this way [6].

maceuticals for personalizing treatments [7].

studies are examined in two groups:

• Pharmacophore analysis

2.Based on target structure

• Molecular docking

• Based drug design

1.Based on effector (ligand) structure

Every patient and disease are different. The personalized treatment approach can be better for each patient requires. The development of individual mechanistic models of the disease process offers the possibility of attaining truly personalized drug-based therapy and diagnosis. At this point, computational methods have provided exciting contributions to pharmaceutical research and development. The need for individual drug design enhances the importance of computational models. Infrared (IR), ultraviolet (UV) and nuclear magnetic resonance (NMR) spectra of the molecule to be predicted, are important and generated by computational approaches in order to characterize molecular structure. The compatibility of the target protein active site with the small molecule (or ligand) is examined, so more

Computer-aided drug design has been established as a valuable tool for the design of new molecules, with many success stories since the 1980s. Pharmaceutical companies have invested substantially in bioinformatics approaches, and it has been predicted that such methodologies will have an important role in pharmacogenomics and personalized medicine. The American Food and Drug Administration (FDA) accepted and expressed the importance of new biomarkers and radiophar-

Mathematical models of drug design are used to guide drug research and development. Computational models provide the identification of the factors involved in the absorption, distribution, metabolism, elimination and access to the target region of the chemical components. It also exposes the dynamics involved in the interaction of the compounds with the target (receptor, enzyme, etc.,). These models are effective in analyzing the fate of drugs that have undergone biotransformation. It helps us to comment on the undesirable effects or toxic effects of drugs and to help us explain drug-drug interactions. The concept of virtual clinical trials and the integrated use of *in silico*, *in vitro* and *in vivo* models in preclinical development could lead to significant gains in efficiency and order of magnitude increases

The targeting agent is used as a starting point for the design of computerassisted drug active substance. Examples of targeting agents include receptors, enzymes, nucleic acids etc. Natural endogenous substances or drugs may be effectors that occupy the effective surface of the targeting agent and affect the target positively or negatively. Computer aided drug molecule design and development

• Quantitative structure-activity relationships analysis (QSAR)

It is aimed to interpret the structure of receptors by using the structure of molecules and acting on ligand structure. In method based on the target structure, it is aimed to design molecules that can act on the basis of the known receptor structure [6].

in the cost effectiveness of drug development and approval [8].

*Molecular Docking and Molecular Dynamics*

than above 1 MeV.

appropriate quality controls [4].

**2. Classification of radiopharmaceuticals**

cals should be done before administration to patients.

With the widespread use of radiopharmaceuticals, the need for specialized pharmacists as known radiopharmacists has increased. Radiopharmaceuticals should be prepared by radiopharmacists and administered by clinicians to the patient. The doses of radiopharmaceuticals are defined either millicurie or microcurie. The pharmaceutical form of the radiopharmaceuticals may be solutions, kit, capsules and aerosols. The amount of active substance in the radiopharmaceutical is at a low dose that does not have a pharmacological effect. The shelf life of a radiopharmaceutical depends on half-life of radionuclide. Quality control of radiopharmaceuti-

A radiopharmaceutical optimal performance should have some characteristics. While the radiopharmaceuticals used for diagnosis emit gamma ray, the radiopharmaceuticals used for treatment emit beta ray. Alpha and beta radiation, which have particle radiation, are not desirable for diagnosis due to high linear energy transfers (LET). Because this energy is completely absorbed in the body, some particles that can escape to the body and cannot reach the crystal in the imaging system [3].

The ideal radionuclide energy for imaging should be around 100–300 kilo electron volts (keV). The quality of image falls when it is above or below these energy values. In radiopharmaceuticals used for treatment, the energy should be higher

Ideally, the effective half-life of a radiopharmaceutical should be greater than about 1.5 times the imaging time. This pro vides a good image between the maximum dose and the minimum dose that can be injected into the patient, so that the counting statistics and image quality are optimal. On the other hand, the effective half-life of radiopharmaceuticals used in treatment is indicated by hours and days. The localization of radiopharmaceuticals should be high in the desired organs or tissues. Low dose for both, patient and personnel, is necessary of ideal radiopharmaceutical. When the radioactivity ratio in the target/non-target area is low and the radiation dose increases in non-target areas, treatment or diagnosis efficiency of radiopharmaceuticals decreases. They must be non-toxic, sterile and pyrogen-free for patient compliance. Finally, radiopharmaceuticals must maintain their chemical stability during usage, should be cheap and easy to find, easy to prepare and

In general, four types of radiopharmaceuticals are used in medical practice. The first of these is ready to use radiopharmaceuticals. These products have a shelf life. Administration to the patient is performed after the radioactive decay is calculated. Iodine (I-123) capsules, I-131 hippurane, Gallium (Ga-67) citrate, Tallium (Tl-201) chloride, Xsenone (Xe-133) aerosol, Technetium (Tc-99 m) pertechnetate are the examples of this group. The second type of radiopharmaceuticals is radiopharmaceuticals obtained from semi-manufactured products. They are prepared by combining the kits with radionuclides that obtained from the generator. The third type of radiopharmaceuticals is prepared directly before use. Products of this group should be prepared and used immediately. Examples of this group are the particle accelerator products. The fourth type of radiopharmaceuticals is based on preparation of samples taken from the patient. The patient's cell or plasma proteins are radiolabeled with radionuclide and given to the same patient. An example of this group is Tc-99 m radiolabelled WBC. The laboratories have different regulations and rules because of this, radiolabelling efficiency and cell viability should be checked for this group after radiolabeling

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process [5].
