When to stop chelation with iv DTPA for GDD. This applies to all heavy metals treated with an optimal chelator. Revision June 16/2025.

I find it useful to write newer versions of critical information. Often in response to questions from patients. A new version may trigger greater clarity, or at least different words, on my part. And writing in different words may click better into patient understanding.

This may be while still brief, more clearly and comprehensively written than earlier versions:

1.  This metric is very important: 80-85% back to yourself is when you think about stopping chelation. Or atleast pausing.

Under the best of circumstances this is a difficult metric, since the frame of reference most people have  is also how you imagine you felt when you were younger. So if you are 5 years out from GDD start, your frame of reference is not how you felt 5 years ago, but how you estimate you should feel 5 years older. That said, the more you know/ learn about everything, there is enormous greyness in essentially everything... with perhaps the exception of Hawkeye and determining if a tennis ball is in or out. Everything else, and with this circumstance: we have to make a wisdom-sense adjustment for what is 85% back to 'normal', as age is a major changing variable, as is the impact of various underlying non GDD diseases.  

2. Post chelation with iv Ca- DTPA urine has dropped to 3 mcg/ 24 hr. The common finding is urine stable at 10- 20 mcg, for 5 or more chelations, and then sudden drop to around 3-5 mcg (3 mcg better).

2A.  The more GBCA injections, the longer is the stable finding of a high post chelation urine number. 

2B. Other factors, like pre-existent major bone injury, also factor in for longer high Gd urine content, reflecting larger than standard amount of Gd in bones. 

This  drop in post chelation 24 hr urine usually reflects that the bone reservoir is now being depleted.. This is key to understand for Gd (and Lead);  [and all other heavy metals]. 

2C. Decrease ot total body heavy metal content is essential to achieve true near cure. So for Gd and Lead this is depleting the largest and most durable reservoir - bone. This is only achieved with repeat chelation and making use of le Chateliere's principle (everything strives to be in equilibrium). Understanding better the interplay of reservoirs is a work in progress for other metals.

 2D. Note comparison between urine results also highly depends on the interval between chelations: the shorter the interval between chelations, the less time for re-equilibration of Gd from bone back to soft tissue, and thus the lower the post chelation Gd. I therefore like the intervals to be stable: we use 4 week intervals, but based on schedule idiosyncrasies this may be 3-5 week intervals. The converse is also  true, the longer the intervals the higher the urine Gad content. All this must be factored in. 

2E. The important exception to the urine metric are Prohance and Dotarem/ Clariscan and presumably the newest agent Gadopiclenol (Elucirem). The post- 1 g Ca-DTPA 24 hour urine may be no greater than 1.5 mcg/24 hours. None-the-less increased Gd removal of these agents still is in the 4 fold range (rather then 20- 40 fold typical with other GBCAs). Still this mildly increased removal is still sufficient to eventually result in near cure.

2F. With these latter agents using a bolus injection technique of the most stable effective chelator (Ca-DTPA) is extremely important, as (in my theory) the powerful chelator is acting like a magnet crane arcade game, tugging fully intact GBCA back into the circulation for renal elimination. Hence with these latter agents, attention to 85% clinical improvement may be the only assessment used for determining when to stop chelation.

2G. Likely all chelations for Gd from GBCAs require bolus injection of DTPA, for atleast 5, perhaps 10 chelations. Regardless if the shift goes to oral. This is because it is critical to emulate with the removal process how the heavy metal has entered the body to begi n with. Virtually all GBCAs everywhere are injected at 2 ml/sec (fast). After that, a fair amount of the Gd in the body may have been moved by re-equilibration, so the dominance of Gd deposition  from rapid iv injection has lessened, as now proportionally more Gd, the re-equilibrated Gd, is closely positioned to the vessel walls.

Richard Semelka, MD