The present invention relates to a compound of formula I, a pharmaceutical composition comprising said compound of formula I, a method of inhibiting indoleamine 2,3-dioxygenase and its use in medicine.本發明涉及式I所示的化合物,包含所述式I化合物的藥物組合物,其抑制吲哚胺2,3-雙加氧酶的方法以及其在醫學上的用途。