I'm not exactly sure how that works.
I'd think that if they billed it as a courtesy then that would leave room for abuse on their end.
Like you I would like to know as well.
Nursing Home or Skilled Nursing I would think would order the drugs and inturn would include it on the patients monthly billing to said insurance company or self pay.
I could not find anything online. Best thing to do I think would be to contact several homes and speak with their billing dept or the administrator and see how it is done as you want to make sure that the pharm company is billing when it is billed the nursing home.