exemastane and androstenetrione are both suicidial type-I aromatase inhibitor's meaning that permanently bind to the aromatase emzyme. exemastane (6-methyl-androst-4-ene-3,17-dione) and androstenetrione (androst-4-ene-3,6,17-trione) the molecular structures almost identical and funtion idential. On a mg per mg and almost molecule per molecule potency not the same. Example a dose of exemastane is 25mg/day with a half life of 13.5hr and androstenetrione is 100mg/dose several times a day with a half life of less than 13.5hr. It doesn't seem that affinity wouldn't be the difference in effect since, it is permanently bound to the enzyme?