Adefovir (Hovalix) drug insert: The “Genotoxicity” section of the drug insert states, “Adefovir was mutagenic in an in vitro murine lymphocytoma cell assay (with or without metabolic activation), but in an in vivo mouse micronucleus assay, adefovir doses up to 2000 mg/day had no chromosome disruptor effect.” “Adefovir induces chromosomal aberrations in human peripheral blood lymphocytes not metabolically activated in in vitro assays. In Ames bacterial reversion mutation assays using Salmonella typhimurium and Escherichia coli (with or without metabolic activation) adefovir was not mutagenic.” Some patients are very scared when they read this paragraph. However, the above-mentioned “in vitro murine lymphocytoma cell test”, “in vitro human peripheral blood lymphocyte test” and “Ames bacterial reversion mutation test in Salmonella typhimurium and Escherichia coli “Only the “mouse micronucleus test” is an in vivo test. The results of in vitro laboratory experiments are far from the human body and cannot represent the effect of the drug in the human body, while in vivo experiments are closer to the effect of the drug in the human body. In addition, although the instructions do not specify the dose of adefovir used in in vitro experiments, the dose of the drug used in general in vitro experiments is often very high because the investigator does not have to worry about the harm caused by the drug. In the in vivo mouse micronucleus experiments, we can also see that a small mouse dosage of adefovir is as high as 2000 mg per day, while our usual dose of adefovir treatment is only 10 mg per day. at such a high dose, no chromosome breakage occurred in the mice, indicating that adefovir has no significant genotoxicity. The “Reproductive Toxicity” section of the drug insert states: “Adefovir has no effect on fertility or reproduction in male or female rats when given orally. There was no embryotoxicity or embryonic malformation in rats or rabbits when adefovir was given orally. In pregnant rats given adefovir intravenously, an increased incidence of embryotoxicity and fetal malformations (generalized edema, eye vesicle depression, umbilical hernia and tail kink) was observed at doses that produced significant maternal toxicity (20 mg/kg/day, equivalent to 38 times the exposure at the recommended therapeutic dose for humans). At an intravenous dose of 2.5 mg/kg/day, equivalent to 12 times the human exposure, no adverse effects were observed.” From this paragraph we can see that scientists did numerous experimental studies, including in male rats, before adefovir was used in humans and found no effects of the drug on fertility or reproduction in male rats. For female animals embryos were affected only at fairly high dosages. It is on the basis of these trials that the FDA’s concern that the drug is harmful to human embryos led to the classification of adefovir as a Level C for safety in pregnancy. The drug insert specifically states in the [Use in Pregnant and Lactating Women] section that “Adefovir should not be used in women who are pregnant if possible” and that “effective contraception is recommended for women of childbearing age treated with adefovir.” However, it does not state that men treated with adefovir use effective contraception, indicating that male patients do not need contraception during treatment with the drug and that their wives can have children. The “Genotoxicity” section of the drug insert states: “Entecavir was found to be a chromosome break inducer in human lymphocyte culture experiments. Entecavir was not found to be a mutation inducer in the Ames assay (using S. typhi, E. coli, with or without metabolic activators), the gene mutation assay, and the Syrian hamster embryo cell transfection assay. Entecavir was also negative in transoral administration micronucleus assays and DNA repair assays in rats.” This paragraph is almost identical to adefovir (Hovirax). Here, I explain again the human lymphocyte culture assay, the Ames assay, the gene mutation assay, the Syrian hamster embryo cell transfection assay, and the micronucleus assay. These tests are all standard combinations of drug genotoxicity tests recommended by the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH.) The latest ICH requirements for standard combinations of drug genotoxicity tests, the ICHS2 (R1) Guidelines for Genotoxicity Testing and Analysis of Results of Pharmaceuticals for Human Use, state. “A compound with a suspected structure is usually sufficient to demonstrate a lack of genotoxicity when the results of either test combination are negative.” Negative results for entecavir in multiple genotoxicity tests indicate that the drug is not genotoxic. The “Reproductive Toxicity” section of the drug insert states, “In a reproductive toxicity study, entecavir was administered for 4 weeks at doses up to 30 mg/kg, and at doses exceeding 90 times the maximum recommended human dose of 1.0 mg/day, no effects on fertility were observed in male and female The fertility of rats was not affected. In toxicology studies with entecavir, degenerative changes of the vas deferens were found in rodents and dogs at doses up to 35 times or more the human dose. In monkey experiments, no testicular alterations were found.” “In reproductive toxicity studies in rats and rabbits, no embryonic or maternal toxicity was found at oral doses of this product up to 200 and 16 mg/kg/day, i.e., 28 times (for rats) and 212 times (for rabbits) the maximum human dose of 1.0 mg/day. In rat experiments, toxic effects of entecavir in embryo-fetal rats (resorption), reduced body weight, abnormal tail and spine morphology and reduced levels of ossification (vertebrae, toes and phalanges), and additional lumbar vertebrae and ribs were observed when female rats were dosed at doses equivalent to 3100 times the human dose. In rabbit experiments, toxic effects (resorption), reduced levels of ossification (hyoid bone), and an increased incidence of the 13th rib were observed in female rabbits dosed at 883 times the human dose of 1.0 mg/day. In studies of oral entecavir in pre- and postnatal rats dosing greater than 94 times the human dose of 1.0 mg/day was found to have no effect on offspring.” The maximum adult dose of entecavir we use in the treatment of hepatitis B is 1 mg/day, and as we can see from the above paragraph, no effects on fertility were found in male and female rats when entecavir was administered 90 times the maximum recommended human dose in animal tests, but degenerative changes in the vas deferens were found in rodent tests with dogs, and in monkey experiments, no changes in the testes were found. Nevertheless, one can see that the doses used in the animal tests far exceeded the human therapeutic dosage. Therefore, there is no effect on male fertility at the human therapeutic dose. Similar to adefovir, entecavir had some effect on embryos in animals when the dose was increased to 883 to 3100 times the human therapeutic dose. Therefore, the US FDA is concerned that the drug is harmful to human embryos and has classified entecavir as Class C for safety in pregnancy. The drug insert specifically states in the [Use in Pregnant and Lactating Women] section that “The effects of entecavir in pregnant women have not been adequately studied. This product should be used only when the potential risk benefit to the fetus has been adequately weighed.” However, there is no indication that the use of entecavir in male patients whose wives cannot have children or that it has an effect on fertility in male patients.