A drug therapy used to prevent the development of certain infections. There are two types. Primary prophylaxis is taken to prevent the onset of infections that have not developed. Secondary prophylaxis is taken after the successful treatment of an infection to prevent its recurrence. Prophylactic therapy is important in HIV as it helps prevent many opportunistic infections, but the best primary prophylactic therapy for HIV is to take daily HIV antiretroviral treatment (which prevents opportunistic infections from arising).