I'd try first foot-soaking in the 1/8 tsp Borax per liter of water solution.
I read you can absorb ALL of it. I'd think if the ankles swell - maybe you do absorb all or most. I don't know what would be the max tissue capacities to handle it but I just found this link: http://www.hc-sc.gc.ca/dhp-mps/pubs/natur/boron-bore-eng.php#a14
I'd say - keep daily dose 20 mg pure Boron at most. As per my previous msg:
I was trying to figure out a therapeutic dosage of Borax.
If I put 1/8 of tsp in 1.2 l water, does it make sense to drink 200 ml each day, getting about 20 mg of pure Boron as per the following calculation? //www.curezone.org/forums/am.asp?i=1916398