User talk:Cdswingle

Addition to potassium iodide article
Nice information addition. I'll probably move it down to be closer to the section on use of KI to block accidental I-131 contamination, so the flow is better.

I've also copied most of it to the article on MIBG, which has some nice images of unwanted radioiodine from MIBG metabolism getting into the thryoid. So far as I can tell, MIBG is probably the major radioiodine containing pharmaceutical used, with I-125-fibrinogen running a distant second. Is that your impression as well?

What's your expertise in these areas, if you don't mind me asking?

Reading the cited recommendations you put in, I see that they are a little more stringent from I-131 than for I-123, but I'm surprised that they aren't a LOT more stringent. I-131 is at least 20 times as carcinogenic to the thyroid per unit of scintigraphic activity, so I would think they'd be 20 times more careful with the stuff in non-thryoid targetted radiopharmaceuticals.

And I"m really amazed that they don't give iodine to newborns getting MIBG. This just seems incredibly stupid. Do you see the thyroid in the MIBG article? I have no doubt you can see it if you give MIBG to a newborn, too. There seems to be an assumption that a newborn is being blocked with iodine in mother's milk, but how do they assume all nursing mothers are iodine-replete?

Some of your new info may find its way into the isotopes of iodine article, also.

Welcome to Wikipedia. S B Harris 23:48, 30 July 2010 (UTC)

Sorry it took so long for me to reply. Still getting this whole Wikipedia thing figured out.

As far as my expertise in the area, I certainly don't mind sharing. I am a PharmD student at the University of Oklahoma, and have worked for 3 years at the nuclear pharmacy inside OU's College of Pharmacy, which is staffed by one Authorized Nuclear Pharmacist and 5 Board of Pharmaceutical Specialties Certified Nuclear Pharmacists. I obtained Authorized User status myself, this June.

First, let me thank you for letting me know what you think, and copying the information to the MIBG article. As far as my personal experience goes, your assumption that MIBG is the primary radioiodine containing pharmaceutical used is certainly correct as far as diagnostic scintigraphy. However, tositumomab, brand name Bexxar, is a radioiodine containing radiopharmaceutical used in the treatment of Non-Hodgkin's Lymphoma. It too requires thyroid blocking, which I believe is discussed either in the product labeling, or in the supplementary material provided by the manufacturer, GlaxoSmithKline. I have not personally dispensed any I-125-containing pharmaceuticals. I supposed this is due to its limited utility as a scintigraphic agent and the understandable hesitation of nuclear medicine departments to draw serum samples.

In the MIBG article, the thyroid is blatantly visible to even myself (reading and interpreting the images is certainly outside my scope of practice), and I should hope that the uptake is due to patient noncompliance with SSKI or some kind of similar situation. I'm quite certain all nuclear medicine departments have their own in-house guidelines on thyroid blockade by age, including newborns, and that each facility is different. A deficit exists in current guidelines as to this procedure. From my discussions with local nuclear medicine technologists, JCAHO accreditation of nuclear medicine departments in the United States enforces compliance with ACR (American College of Radiology) Practice Guidelines, which, in my personal opinion, are lacking for neuroendocrine scintigraphy with MIBG. That being said, of course, I believe (or would hope to believe) the same as you: that failure to give SSKI or Lugol's to newborns undergoing MIBG scintigraphy is an uncomfortable situation to say the least. The European Association of Nuclear Medicine recommends the use of potassium iodide in all age groups, and I believe rightly so. The Children's Hospital associated with the University of Oklahoma does premedicate all age groups with potassium iodide; however, I cannot vouch for procedures at other institutions. I should hope that no hospital makes assumptions of a child's breastfeeding status, nor the iodine content of that milk. The benefit of exogenous KI administration in this situation far outweighs the risk.

As far as being 20 times more cautious with I-131 than with I-123, I believe a medical physicist would be more able to address this. However, my first thought (to be read: assumption) is that the duration of KI dosing is related to the effective half-life of I-123 is shorter than that of I-131 because the physical half-life is shorter, 13.3h and 8.02d, respectively. I am unsure of the biological half-life of iodine not incorporated into thyroid hormone. While I can appreciate the concern over the carcinogenic potential of different isotopes of iodine, the immediate concern of free iodine is the potential for irrevocable damage to the thyroid, which is seen with I-131 alone.

To illustrate the point, consider that I-131 sodium iodide is generally used therapeutically for diseases of hyperthyroidism such as thyroid cancer and Grave's Disease. It's mechanism of action is the beta particle emission, which reduces the volume of viable thyroid tissue producing T3 and T4 hormone. However, I-123 is used diagnostically for evaluation of iodine uptake by the thyroid gland. Its utility is derived from its gamma photon emission and distinct lack of significant alpha and beta particle emissions. Thus, the prevailing dangers of any circulating free iodine localizing in the thyroid gland is dependent primarily on the type of emission. On a more morbid note, MIBG is most often used to verify the presence of neuroblastoma. The life expectancy of neuroblastoma patients, while improving as a whole, is still generally abysmal. While in no way do I champion higher-than-necessary doses to any organ for any reason, the carcinogenic effects of such a small radiation dose from I-123 to their thyroids truly pales in comparison to the very real side effects of the chemotherapy used to treat the cancer, which also include carcinogenesis.

Let me know if you have any more questions, comments, etc. I will be happy to follow up with you.

Cdswingle (talk) 02:56, 11 August 2010 (UTC)