Metrifonate (INN) or trichlorfon (USAN) is an irreversible organophosphate acetylcholinesterase inhibitor. It is a prodrug which is activated non-enzymatically into 2,2-dichlorovinyl dimethyl phosphate (DDVP). It is used as an insecticide. It can be used to treat schistosomiasis caused by Schistoma haematobium, but is no longer commercially available. It has been proposed for use in treatment of Alzheimer's disease, but use for that purpose is not currently recommended.