prolonging the time of therapy were observed.6,18 We currently have the formulations interferon α, pegylated interferon α and human interferon α 2b. Pegylated interferon α has shown greater efficacy and easier administration when compared to the conventional one. The interferon α 2b formulation has also shown good results in HBeAg positive patients, with 50% seroconversion to anti-HBe. In addition to these formulations, interferon λ has been recently described, which belongs to the class of type III interferon, however little is known about them. Studies in murine liver cells have shown that interferon λ is able to inhibit HBV replication with the same efficiency as interferon α. In humans, however, the results are still not well defined.19 Interferons are rarely tolerated due to their severe side effects, which involve flu-like illnesses, anorexia, autoimmune disease outbreaks, thyroid dysfunction, myelosuppression, hepatitis outbreaks, hepatic decompensation and adverse neuropsychiatric events such as depression, irritability and eventual moodiness to suicide10 Interferon-α Interfero-α (IFN-α) was the first drug licensed for the treatment of hepatitis B. IFN has two forms of presentation, conventional or pegylated (peginterferon). Pegylation allows the drug to work longer in the body. The pregylation process covalently binds an Interferon molecule to a polyethylene glycol molecule.20 Interferons are glycoproteins that have numerous biological behaviors, including antiviral, immunomodulatory, and complex antiproliferative consequences. Its endogenous production and release occurs in response to viruses and other inducers, with the exception of bacterial exotoxins, polyanions, some low molecular weight compounds and microorganisms with intracellular growth.21,22 It points out that the mechanism by which recombinant human interferon alpha 2a and other types of interferon carry out anti-tumor and antiviral activity is not entirely common. However, it is believed that a direct antiproliferative action on the inhibition of viral replication and modulation of the host’s immune response plays an important role in the antiviral activity.16 According to the data demonstrated by ANVISA, the advantage of administering Interferon alpha is the treatment for a defined period (48-52weeks), but side effects and contraindications may arise in patients with decompensated liver cirrhosis. Interferon alpha 2a is required to be used under medical advice. People with abnormal kidney, liver and bone marrow function should be carefully monitored.2 Ordinance No. 2561/09 shows that care must be taken when using recombinant human interferon alpha 2a in people with myelosuppression (suppression of the bone marrow blood cell production function), as recombinant human interferon alpha 2a can cause reduction of the white blood cells.2 This parameter should be carefully monitored prior to initiation of interferon alpha 2a therapy and at designated times during therapy. Complete blood tests must be performed periodically.16 The most frequent adverse reactions have flu-like symptoms such as fatigue, fever, chills, muscle pain, headache, joint pain, sweating, among others. They may also present gastrointestinal changes, such as anorexia, nausea, vomiting, change in taste, weight loss, diarrhea, abdominal pain, constipation, flatulence.2 Liver function should also be noted, some patients had increased levels of alkaline phosphatase, lactic acid, dehydrogenase and bilirubin. Normally the dose of recombinant human interferon alpha 2a should not be adjusted when such reactions occur.2,23 Reactions can also affect the central nervous system, causing dizziness; visual disturbances, memory loss, depression, drowsiness, anxiety, nervousness and insomnia were observed in rare cases and peripheral nervous system, showing paresthesia, torpor, weakness.2,23 Skin changes in the form of Herpes, rash, itching and dry skin that are occasionally reported. Hair loss has been observed in one fifth of patients receiving recombinant human interferon alpha 2a. In the urinary system, according to the author, renal failure was rarely Drug treatment of chronic hepatitis b in Brazil: a review 185 Copyright: