Once the causative agent and affected body system have been identified, specific therapy to cure the infectious disease can begin. The perfect anti-infective agent destroys pathogens while preserving host cells, is effective against many organisms while not promoting the development of resistance, distributes to necessary tissues, and remains in the body for relatively long periods. Because no available antimicrobial meets all these criteria, healthcare providers look for an agent that is effective, has little toxicity, can be administered with relative convenience, and is cost effective. In the process of selection, characteristics of both the client and the infecting organism are considered. Treatment of an infection is not focused on the newest agent, the use of multiple agents, or using samples of agents in the office.