What is the commonality between the antibiotic arsphenamine and azodye?

(N/A) Arsphenamine,also known as salvarsan,is a synthetic organic arsenic compound that was historically used to treat syphilis. It contains an $-As=As-$ linkage.
Azodyes are a class of compounds that contain an $-N=N-$ linkage. The structural similarity lies in the presence of a double bond between two identical atoms ($-As=As-$ in arsphenamine and $-N=N-$ in azodye).