Tenofovir has the same disadvantage as adefovir in that it has the potential for nephrotoxicity. The good news is that its nephrotoxicity is not serious, causing only a mild drop in blood phosphorus or an increase in serum creatinine levels, with an incidence of less than 1%, and mostly does not affect treatment. However, patients should still monitor blood phosphorus and serum creatinine frequently during treatment. Tenofovir also has the great advantage that it is classified by the U.S. FDA as a class B drug for safety during pregnancy and has been used for mother-to-child blockade of AIDS. By January of this year, the U.S. Registry of Antiretroviral Drugs for Pregnant Women had collected more than 800 cases of pregnant women treated with tenofovir, and the babies were born with no higher rate of abnormalities than in the general population. This indicates that this drug is also relatively safe for use in pregnant women. However, because this drug has an effect on renal phosphorus reabsorption, it may affect the bone density of the fetus, and care should be taken to eat more phosphorus-containing foods when taking it during pregnancy.