Blackening Fingers

My brother-in-law has been having the issue of his fingers turning black to the point getting infection and having to have them amputated. He also seems to have sores all over his body and even has had to have them lanced on genitals. Is there some type of blood disorder that this could be associated with or maybe so type of disease? The physician has also said that he now has kidney damage from to many antibiotics. I would appreciate any help or suggestions anyone could give me.