Pharmaceuticals are substances used to diagnose, treat or prevent disease. Radiopharmaceuticals are radioactive pharmaceuticals used in nuclear medicine. These drugs are made up of two components; a radioactive isotope that can be injected safely into the body, and a carrier molecule which delivers the isotope to the area to be treated or examined.

One popular nuclear ingredient is an isotope called technetium (Tc), the lightest radioactive element known, which is used in a variety of nuclear tests. Thallium-201 is used for cardiac stress tests. Other common nuclear components in radiopharmaceuticals include indium-111, gallium-67, iodine-123, iodine-131 and venom-133.

The majority of nuclear medicine involves diagnostic testing. When radiopharmaceuticals are injected into the body, they emit a radioactive signal which can be traced with special cameras or computers. The amount of radiation a patient is subjected to is about the same as a normal x-ray, but the information gathered is significantly different. Non-nuclear diagnostic methods, such as x-rays and ultrasounds, show the size and shape of a bone, organ or tumor. Nuclear medicine allows a doctor to see how an organ is functioning.

Once radiopharmaceuticals enter the body and travel to an organ, they begin to interact with the processes of that organ. The radioactive component emits signals which are picked up by cameras or computers and used to map the process. For example, an ultrasound can show an image of an organ and reveal if a tumor or other abnormality is present. Nuclear medicine can show how the process of glucose metabolism is functioning in the organ.

Nuclear diagnostic testing can be performed on almost every organ of the body. There are currently over 100 nuclear medical exams, with more being developed. Some of these include brain scans, bone scans, cardiac stress tests and thyroid studies. Prior to the test, the radiopharmaceutical is administered to the patient orally, intravenously, or by inhalation. The radioactive material is short-lived, and either converts to a non-radioactive substance, or passes quickly through the body.

Two of the most commonly used pieces of nuclear imaging equipment are the PET and SPECT scans. Positron emission tomography (PET) scans use cameras and computers to construct three-dimensional images of the area being examined. The single photon emission computerized tomography (SPECT) scan creates cross-sectional images of an area. The SPECT scan emits gamma rays, while the PET scan emits photons which convert to gamma rays.

The radiation in radiopharmaceuticals does not harm cells growing at a normal rate. It can, however, destroy fast growing cells. Since most cancer cells grow very rapidly, radiation treatment is frequently used to destroy cancerous tumors. Radioactive iodine (I-131) capsules are administered to treat some types of thyroid cancer. A drug called Quadramet® is given intravenously to relieve pain caused by bone cancer.

The use of radiopharmaceuticals is expected to increase rapidly as new diagnostic methods are developed. Nuclear medicine is being considered for use in infection imaging, neurology and other fields. At this time, most therapeutic radiopharmaceuticals involve the treatment of cancer. On-going research is being conducted to expand nuclear medicines to treat other diseases as well.