My googling failed to turn up the reason for the shortage, other than some unspecified problem that caused the old manufacturer of the active ingredient (melarsomine dihydrochloride) to stop making it, and the drug company scrambling to find a another domestic manufacturer to make it (the FDA is disallowing foreign suppliers, for whatever reason).
Since melarsomine dihydrochloride contains arsenic, I suspect the EPA had something to do with the old manufacturer getting out of the business. Reporters in the current climate seem reluctant to trace problems back to the Obama administration's own policies.
There seems to have been some general more restrictive controls on some medicinal products. Three times in the past I’d ordered the product: Arnica tincture. It was labeled “For External Use Only”. I was prepared to order it again a couple of months back and was told that it is no longer available without a prescription. The only way I could obtain it now is for my doctor to order it, have it shipped to him, and then write me a prescription for it.
All it is is an herbal flower extracted in alcohol, so I’m just making a batch myself. But that is a weird new restriction as it is only mildly toxic and less toxic than many OTC products. It’s sold by homeopathic manufacturers and other tinctures of any degree of toxicity are also no longer available.