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AN-DTPA ... additional information- revised

I consulted with an expert on molecular pharmacy, Michael Jay, PhD, about AN-DTPA and toxicity, and this is what he sent back to me:

The AN-DTPA kit is used to prepare 99mTc-DTPA by reacting DTPA with 99mTc-pertchnetate (the product of a 99Mo/99mTc generator) in the presence of tin (Sn) ions. Sn is used to reduce the unreactive 99mTc-pertchnetate to the highly reactive 99mTc(+4) oxidation state which then binds with DTPA. The specific activity (mCi/mg) of 99mTc-pertchnetate is usually extremely high so the mass of 99mTc used in this reaction is very small. Thus, it is very unlikely (next to impossible) that any of the observed toxicity is due to 99mTc. Thus. The toxicity must be due to the DTPA or the Sn. However, nearly every 99mTc-based radiopharmaceutical kit contains Sn, so any Sn-related toxicity would not be limited to AN-DTPA, but would be observed in other radiopharmaceuticals.

DTPA and tin are the largest components of the kit, so Mike favors tin toxicity (which would explain the metal taste) and DTPA, and DTPA because it redistributes other heavy metals. Tc is so small in amount he does not consider it likely.

So Mike favors Tin and redistributed other metals from DTPA. I favor tin (I had not been aware of how Tc 99m-DTPA was prepared previously), then Tc, then pertechnetate, then DTPA from redistributed other metals. Immunologic reaction still occurs when quantities of an agent are small (think vaccines) so that is why I include Tc.

The bottom line remains: AN-DTPA is not Ca-/Zn-DTPA.

Richard Semelka, MD


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