Anti-D 300 is an Anti-D (Rh) immunoglobulin injection used to prevent Rh disease in Rh-negative individuals, particularly RhD-negative mothers with RhD-positive babies, to prevent them from forming their own antibodies. It is administered during the third trimester of pregnancy and after childbirth to RhD-negative mothers, as well as following Rh-positive blood transfusions in RhD-negative people.