Pediarix is not FDA approved for doses four or five of the DTaP series. This makes sense because using Pediarix for the 4th and 5th doses would result in a lot of extra doses of Hepatitis B. If the child received a birth dose of Hepatitis B vaccine and then 4 or 5 doses of Pediarix, that would mean the child received 5 or 6 doses of Hepatitis B vaccine, which is far more than is recommended and far more than anyone needs.