Drug application after appearance of clinical signs may eliminate or damage pathogens/parasite and lead to recovery of health in the patient.

Chemotherapy (CT) and chemoprophylaxis (CP) are experimental sciences dealing with drugs that selectively inhibit or destroy parasites or other pathogens. Thus, attention to selective toxicity of antiparasitic drugs is central to CP and CT, and useful chemotherapeutic agents should affect the parasite more adversely than the host. Until now, there is no completely safe drug. Knowledge of sources of drugs (pharmacognosy), action and fate in the body (pharmacodynamics), use in the treatment of disease (therapeutics), adverse effects (toxicology) and contraindications is a must to evaluate potential risks as well as possible benefits of drugs to the patient’s well-being.

Claims made by the drug manufacturer for a drug in treatment of target animals consumed by humans...