Ribavirin is an anti-viral drug which is active against a number of DNA and RNA viruses. It is a member of the nucleoside antimetabolite drugs that interfere with duplication of viral genetic material. Though not effective against all viruses, ribavirin is remarkable as a small molecule for its wide range of activity, including important activities against influenzas, flaviviruses and agents of many viral hemorrhagic fevers.Ribavirin is a pro-drug, meaning that it is a chemical precursor for the actual pharmacologically active molecule. When the pro-drug is administered, the body converts it into the desired chemical. Ribavirin is activated by cellular kinases which change it into the 5' triphosphate nucleotide. The primary observed serious adverse side-effect of ribavirin is hemolytic anemia, which may worsen preexisting cardiac disease. The mechanism for this effect is unknown. It is dose-dependent and may sometimes be compensated by decreasing dose.