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Potassium iodide and thyroid protection

  1. Jan 27, 2017 #1
    Hi,
    Does anyone know the reason why we use potassium iodide for thyroid protection in case of nuclear accidental event, and not sodium iodide, or lithium iodide ? (as alkali metals can give away one electron)
    Thanks.
     
  2. jcsd
  3. Jan 27, 2017 #2

    TeethWhitener

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    You can't use lithium iodide because lithium is pharmacologically active (it's used to treat bipolar disorder, among other things), and toxic in large doses. As for sodium iodide, I'm not really sure, but KI is much less deliquescent than NaI, so it might keep longer in suboptimal storage conditions.
     
  4. Jan 27, 2017 #3

    Borek

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    Isn't sodium also a potential problem for those with the high blood pressure?
     
  5. Jan 27, 2017 #4

    TeethWhitener

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    The recommended dosage for adults of KI as a "thyroid blockade" is 130 mg per day. If you switch out the potassium for sodium, the total amount of sodium would be somewhere around 10mg, which is essentially negligible.
     
  6. Jan 28, 2017 #5

    Borek

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    Good point.
     
  7. Jan 28, 2017 #6
    About toxicity of lithium :

    If I do not make mistakes, the molar mass of KI is 39.10 + 126.90 = 166 g/mol.

    Giving 130 mg of KI means giving 130 x E-3 / 166 = 7.83 x E-4 mol of KI and so, the same amount of iodine.

    I then understand that 7.83 x E-4 mol of iodine are recommended for blocking the thyroid absorption.

    Suppose now that we use lithium iodide. Giving the required amount of iodine means to give 7.83 x E-4 mol of lithium, that is (roughly) 0.8 mmol.

    Well, I read that the normal range for lithium in blood is between 0.6 and 0.8 mmol/L (of blood).

    So, giving a pill containing 0.8 mmol doesn’t seem to be toxic (as the amount of blood is +- 5 L).

    But maybe lithium does not rapidly metabolize, so that the amount in blood will dangerously increase…

    Is it correct ?
     
  8. Jan 28, 2017 #7

    BillTre

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    Radioactive iodine would be sequestered to the thyroid because the thyroid uses iodine to make active thyroid hormone.
    If a nuclear war were to happen a lot of iodine might be ingested. It would then be concentrated in the thyroid and kill it by radiation. (By sister had a treatment like this for a thyroid cancer.)
    By taking large amounts of non-radioactive iodine, either the transport of sequestration mechanisms for iodine are flooded with non-radioactive iodine and any subsequently ingested radioactive iodine is not concentrated in the thyroid.
    link
     
  9. Jan 28, 2017 #8

    TeethWhitener

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    This is the acceptable level of lithium in the blood of patients being given lithium medication for treatment of bipolar disorder. The normal range of lithium for individuals not specifically on lithium treatment is in the parts per billion range.
     
  10. Jan 29, 2017 #9

    Borek

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    ppb would be surprisingly low, tap water contains ppm levels of lithium, three orders of magnitude higher.
     
  11. Jan 29, 2017 #10
    Well, I couldn't find normal ranges for blood lithium for a "normal" person ("Mr/Ms Everyone") but I accept that 0.8 mmol/L would be a real upper limit for that normal person, and something not to be done routinely when safer alternatives exist. So, bye bye lithium.

    On the other hand, it seems that normal range for potassium is 3 to 5 mmol/L (http://emedicine.medscape.com/article/2172316-overview) and more than 7 mmol/L is dangerous (http://www.healthline.com/health/high-potassium-hyperkalemia)

    Giving 7.83 x E-4 mol of KI is giving 7.83 x E-4 mol of K ; clearly this dosage is not dangerous. This seems to me to explain enough why potassium is used and not lithium.

    OK. One part of my previous question is solved. But why not sodium ? Normal value for sodium is about 140 mmol/L. So, giving a pill containing 7.83 x E-4 mol of Na looks much safer than giving a pill containing 7.83 x E-4 mol of K...
     
  12. Jan 29, 2017 #11

    TeethWhitener

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    I was going based on this link:
    https://en.m.wikipedia.org/wiki/Composition_of_the_human_body
    But of course it could be wrong.

    Again, for sodium, the only thing I can think is shelf life. Sodium iodide is highly deliquescent, whereas potassium iodide isn't. But I don't know if that's the only reason.
     
  13. Jan 29, 2017 #12

    jim mcnamara

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    Potassium iodide is the gold standard. Meaning in medicine: it has done well in this medical context before, with the least amount of side effects. So why mess around with it? That is the answer. Physicians are the ultimate pragmatists. Ad hoc experimentation is not always safe. Good previous experience counts enormously. NB: excess iodine can do bad things to people(see link). And the whole idea here is get excess safe iodine into the thyroid and its input pathways quickly.

    Sodium iodide is common in multi-mineral tablets. So, both are acceptable in that sense. But the pill dosage is really low, ~150μg. Instead of me going over everything here is good link:
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3976240/
     
  14. Jan 29, 2017 #13

    Ygggdrasil

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    Not sure this is the case with KI, but in many cases when formulating a drug, the identity of the counterion can have important effects on the stability and bioavailability of the drug: http://www.pharmtech.com/salt-selection-drug-development [Broken]
     
    Last edited by a moderator: May 8, 2017
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