DTPA chelation protocols May 2021.

The standard chelation strategy we use, also from the start of our clinical efforts is: Ca-DTPA day 1, Zn-DTPA day 2. We use a more simplified strategy than in our initial publication in Investigative Radiology, in part so it can be replicated at all centers.

Patient seated in reclining chair

1. 1 liter Normal saline bag.

2. iv start 22-24 g catheter.

3. start iv at medium pace. The concept is the full liter should go in over a 1 hour period.

4. May start with iv immune dampening.* proprietary at present

5. 5 ml vial of Ca-DTPA drawn into a 10 ml syringe.

6. inject 2.5 ml Ca-DTPA over 1 minute.

7. at 40 minutes patient to recline in chair with legs up.

8. May inject iv immune dampening * proprietary.

9. at 50 minutes inject the remaining 2.5 ml Ca-DTPA over 1 minute.

Repeat on day 2 same steps with Zn-DTPA.

Variations:

1. Single day Ca-DTPA. Aggressive 1 day treatment. Removes more Gd, but also other metals. So supplementation a few days after chelation may be necessary- but does not seem so, if a good diet is consumed.

2. Single day Zn-DTPA. Gentle 1 day chelation. Also more specific removal of just heavy metals. No supplementation of metals needed.

3. 1/2 dose Zn-DTPA (still given as split dose).

Rational for hand push: to simulate the dynamic injection of the GBCA to begin with - to chase down the GBCA as it was administered. Drip infusion may not penetrate deeply enough into organs and interstitial tissues (using Iodine contrast CT and GBCA- MR comparing drip to bolus injection as the comparator to the DTPA technique).

Rationale split dose. Decreases the Flare response of one large 5ml dose at once. The second split dose removes Gd that was loosened but not removed by the first split dose (theory). So a double chelation in one sitting.

DTPA is extremely safe, and because of this, is widely used in medicine: the basic ligand for Magnevist - 100 million + doses given world-wide to date, and for the nuclear agent Tc-DTPA - millions dose given. Employed for its safety and stability with the metal. The ligand is the safe part of the molecule. No one has studied safety more than I have, and certainly no one has written more in the peer-reviewed literature. So I am very focused and pay attention to all these matters.

If the ligand is a problem in some rare cases, I will report it, but it will need to achieve my recognition of scientific evidence - which GDD did very early on for me. If DTPA is a problem than almost certainly all ligands will also be a problem- and one would have to chose between the risk of untreated GDD (which is generally very dire) and the risk of ligand (which is unknown, and probably if it occurs very minor).

Because with Gd there is the combined aspects of durability of the bone reservoir, potential from electrolyte depletion, and managing effects of Flare from removal and Flare from equilibration; the repetition of chelation sessions we standardly use is every 3 weeks. I have termed this the Goldilocks principle: weekly may have removal Flare adding one onto the next, too late (4 weeks+) re-equilibration Flare becomes severe.

Ofcourse if just Zn-DTPA is used then weekly treatment may be worth trying, especially if it is 1/2 dose Zn-DTPA, since in each session relatively little Gd is removed, hence relatively little impulse for Flare production.

Richard Semelka, MD