Radiopharmacy is an integral part of a Nuclear Medicine Department that deals largely with the preparation, compounding, Quality Control (QC), and dispensing of radio-pharmaceuticals and radioisotopes for human use. Usually, the radiopharmacy comprises a radiochemistry laboratory especially equipped with a dose calibrator, a biological safety class III cabinet for cell labelling or cold kit manufacturing, or a Biological Safety cabinet class II for cell labelling. Radiochemists or radio-pharmacists are the personnel who perform these functions at large hospitals or medical centres. They are involved in manufacturing cold kits and in developing new agents and procedures.

A radio-pharmaceutical may be defined as a pharmaceutical substance containing radioactive atoms within its structure and is administered to humans. It is generally used for diagnostic purposes but may also be used for therapeutic applications. Radio-pharmaceuticals differ from radio-chemicals in that the former have met specific requirements permitting them to be used in humans safely. They are formulated in various chemical and physical forms to target various organs of the body.

The gamma radiation emitted from the radio-pharmaceuticals is detected or measured externally by a gamma camera giving rise to static or dynamic images enabling nuclear physicians to evaluate the functional and/ or morphological characteristics of the organ(s) of interest.

An ideal radio-pharmaceutical is one that rapidly and avidly localises within the organ under investigation, remains in it for the duration of study, and is quickly eliminated from the body. No single ideal agent exists, so a radionuclide and a chemical compound are selected to achieve the best compromise. Basically, the wide range of radio-pharmaceuticals available in nuclear medicine can be divided into four major groups according to application: imaging, in vivo function, in vitro studies, and therapeutic procedures.

Imaging agents:

The majority of radio-pharmaceuticals are used in extremely small tracer amounts for diagnostic imaging which is the main activity of Nuclear Medicine. The selection of an imaging agent is based on its ability to localise within the organ of interest and a gamma camera is used to acquire its dynamic or static image. Dynamic scans are useful for evaluating the functional status of the organ based on the rate of accumulation and clearance of the tracer. Static images provide information on the morphology of the organ (size, shape, presence or absence of space occupying lesions) based on the pattern of radionuclide distribution.

In vivo function agents:

Radioactive tracer agents are also used to measure function of a particular organ by counting radioactivity emitted from the body, in blood samples or in urine. Such studies are based upon the localisation, dilution, concentration, or excretion of radioactivity following administration of the  radio-tracer. For example, ¹³¹I-sodium iodide is used for assessment of thyroid function by determining the percentage of administered radioiodine that is taken up by the gland within a given time, ⁵⁷Co-cyanocobalamin and ⁵⁸Co-cyanocobalamin capsules are given to the patient for measurement of vitamin B₁₂ absorption from the gastro-intestinal tract by measuring the fraction of orally administered radioactive B₁₂ that is excreted in the urine over 24 hours (Schilling's test), and ⁵¹Cr-sodium chromate for determining red cell volume and red cell survival studies by measuring the dilution of a known amount of the intravenously injected ⁵¹Cr-labelled red cells (and ¹²⁵I-HSA to measure plasma volume). It is essential that the chemical integrity of these radio-tracers is not altered as a result of the radiolabelling procedure. ⁵¹Cr-EDTA (Ethylene Diamine Tetraacetic Acid) is frequently used for determining G.F.R.

Agents for In Vitro Studies:

These agents are radio-tracers that are not injected into patients, but used to measure chemical substances, hormones, or drugs in patient's blood sample. The majority of tests are based on the radioimmunoassay (RIA) principle making use of the antigen-antibody immune reaction. These tests are frequently used to measure plasma levels of thyroid hormones, cortisol, digoxin, and a number of other compounds. In many institutions, RIA falls under the domain of Clinical Chemistry/ Chemical Pathology.

Therapeutic Agents:

The commonest therapeutic procedure is the use of ¹³¹I- sodium iodide for the treatment of hyperthyroidism and ablation of residual functioning thyroid tissue in differentiated thyroid carcinoma. With an intent to selectively destroy diseased tissue, various other beta emitters are occasionally used as an adjunct to conventional procedures cancer therapy. For instance, ¹¹¹In-pentetreotide (¹¹¹In-octreoscan) has been used as an adjunct in the diagnosis and management of somatostatin receptor-bearing gastro-enteropancreatic neuroendocrine and carcinoid tumours. In clinical trials, ¹⁶⁶Ho-DOTMP has been used for bone marrow ablation as an attempt to treat terminal stage multiple myeloma. ⁸⁹Sr-Strontium chloride ('metastron') and ¹⁵³Sm-EDTMP are used as alternatives and adjunct to external beam therapy for the palliation of bone pain from bone metastasis secondary to prostate carcinoma following failure of hormone or chemotherapy. Occasionally, ³²P-sodium phosphate also has been used for treatment of polycythemia.

Radioisotopes:

The following is a list of commonly used radioisotopes in Nuclear Medicine. Follow the link to learn more about each particular isotope.