Abstract: The invention provides the use of a pyrano[2,3-d:6,5-d′] dipyrimidine derivative for the manufacture of a medicine for the treatment of a retroviral infection in a mammal. It also provides a product containing: (a) one or more derivatives of a pyrano[2,3-d:6,5-d′] dipyrimidine; and (b) one or more anti-retroviral drugs, including drugs effective against one or more retroviral or cellular proteins involved in the entry and/or replication of a retrovirus, in respective proportions such as to provide a synergistic effect against a retroviral infection in a mammal, as a combined preparation for simultaneous, separate or sequential use in retroviral infection therapy.