A 'remedy' is something that addresses or solves a problem/issue-- it could be medical, legal, or as a general use. In a legal sense, it is something that corrects or addresses a legal wrongdoing. It's basically a 'solution.' An 'agent' is generally something that does something. Like a 'causative agent,' would be whatever, on a basic level, causes a problem or causes the state/status of whatever you're talking about. It's basically the 'cause.'