 First it is monophosphorylated by adenosine phosphotransferase and then the monophosphate is converted to carbovir 3´-monophosphate.Subsequently, it is fully phosphorylated and the carbovir is incorporated by the RT into the DNA chain and acts as a chain terminator.Carbovir is a related guanosine analogue that had poor oral bioavailability and thus was withdrawn from clinical development.