The Food and Drug Administration on Friday approved Gilead Science's drug Hepsera (adefovir dipivoxil) for the treatment of hepatitis B. The drug was originally developed as a treatment for HIV disease but was rejected by the FDA in 1999 because of concerns over kidney toxicity at high doses. Hepsera is given at lower doses for the treatment of hepatitis B. The drug, a nucleotide reverse transcriptase inhibitor, works by blocking replication of the hepatitis B virus. It is administered once a day as a 10-milligram tablet and was immediately made available by Gilead upon FDA approval. Hepsera is the first medication to be approved by the federal agency for the treatment of chronic hepatitis B infection in more than five years and is one of only three treatments available.