yes dmsa is otc, but from what i understand, especially after learning about dr. buttar's experiences, dmps is the way to go. try to find a doc and get the scrip... the original formulation for dmps was for oral use. i talked with one of their reps who had some choice (not very nice) words to say about it being administered intravenously.
if you can tolerate dmsa and it is doing the job then no problems.