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What are 'radiopharmaceuticals'?


Hossein Jadvar (Doctor) gives expert video advice on: How are radiopharmaceuticals made?; What are examples of radiopharmaceuticals?; Are there radiation risks of radiopharmaceuticals? and more...

What are 'radiopharmaceuticals'?

Radiopharmaceuticals are basically pharmaceuticals which have been labelled with radioactive material, a variety of radioactive material. That radioactive material is like a light beacon, that's the one that gives the gamma rays out, or in the case of positron emission tomography, it's a positron label that gives off positrons. Basically they act as a light beacon, following where the pharmaceutical is distributing in the body, and that's the reason we call it radiopharmaceuticals.

How are radiopharmaceuticals made?

Well, there is a whole branch that we call radiochemistry, and that is very active. It is not only clinical but also a research area. In radiochemistry, basically, we design pharmaceuticals from scratch depending upon what we know or understand about the physiology of a question. Then, these pharmaceuticals are designed based on that, and then depending on what that chemistry is, what that pharmacy of that chemistry is, then a radioactive material can be placed in a certain part of that molecule that is chemically stable and is useful. So actually, it is a rather complex field. As I said, there are people who get doctorates in radiochemistry which designs these kinds of things. It is a very exciting field because we have to understand physiology, biochemistry, chemistry and radioactivity, physics basically.

What are examples of radiopharmaceuticals?

In general nuclear medicine, for example, we use Technetium-99m MDP. That is a tracer that we use for looking at bone metastasise or bone turnover. It's used for a variety of reasons for looking at infection, inflammation, and for looking at cancer in the bone. It's a very common radio-tracer. We have tracers that are used for looking at cardiology, looking at myocardial profusion, for example. Some of them are like Technetium-99m Sestamibi, maybe Technetium-99m Tetrotosmin, Thallium-201 chloride. These are all tracers with the majority of their use in nuclear cardiology, although it's not exclusively for nuclear cardiology. There are other applications for every one of these. In Position Emission Tomography the most important tracer is F-18, Fluorodeoxyglucose, or in short they call it FDG. That's the one we use every day in the clinic, as they call FDG-PET. That is essentially an analog of glucose molecule and is a very important radiopharmaceutical for PET imaging, but there's a huge list of radio tracers that are available. These are just a very few that I mentioned that are some of the major ones.

How are radiopharmaceuticals administered?

Radiopharmaceuticals are administered from a variety of ways, mostly intravenously. But also they can be administered orally, they can be administered through a puncture into the abdomen, the peritoneal, or what we call the peritoneal cavity. As I said though, the most common route for administration is intravenous.

What happens to radiopharmaceuticals once inside my body?

Once a radio-pharmaceutical is inside your body, basically it depends on the radio-pharmaceutical. The chemistry of the radio-pharmaceutical dictates how, basically it distributes in the body and they go to an appropriate place and accumulate there for us to be able to image them. For example, if we give a technician a ninety-nine system, amibbi which is for looking at profusion, for looking at how the heart muscle is being pro-fused, it basically goes to the heart muscle through the coronary arteries It distributes into the substance of the muscle. It happens that maybe in the system it goes to the myocardium which is the constituent of the cells and that's how it distributes into the myocardium. It does not change. It does not redistribute and we are able to make an image of the distribution in the myocardial which is dependent on how well that myocardial is being pro-fused. So, if it's not pro-fused well because of a problem or a disease in the coronary artery because of coronary artery disease, then the delivery of this tracer is reduced in the myocardial in that are of the myocardium and that's what we see and report as what we call ischemia. There's a shortage of blood to that area of the myocardium.

Are there any side effects of radiopharmaceuticals?

Well, they have been used for many, many decades and there are some side effects which are very minor. Some, are just like any other pharmaceuticals that may be used, for example, there could be allergic reactions but these are far and between, and very rare. And so these are, by far, they don't have any major side effect at all and have been used safely, as I said, for decades.

Are there radiation risks of radiopharmaceuticals?

Because it is radioactive material, obviously there is some radiation risk, but these are very small. It has to be taken into consideration that these studies are only done or administered when there is a need for it. It is not as if everybody goes and has a nuclear medicine study. If there is a need for it, then it is justified to use a small amount of radioactivity through regular pharmaceuticals, for example for making a diagnosis or treating a patient.

What is 'physical half life' in relation to radionuclides?

The physical half life is defined by the amount of time for that radioactive element to decay to half of its original radioactivity. The physical half life for "f18", for example "nfdg" is 110 minutes. For technetium "99m" in some traces, for example, "mdp or system maybe that's 6 hours. The physical half life of "I131" which is used in radioiodine treatment of thyroid cancer, is 8 days.

What is 'effective half life' in relation to radionuclides?

I mentioned a physical half life of the radionuclides for some of the major radionuclides that we use in nuclear medicine. However, the effective half life can be quite shorter than what I mentioned before, because it also takes into consideration the biological half life of the radiotracer, which is dictated by the physiological processes in the human body. Therefore, the effective half life is the more important term in comparison to the physical half lives that we talked about, taking into consideration the physiology and chemistry of the particular radiotracer, and are generally much shorter than the physical half lives.