ANTI HEPATITIS VIRAL AGENTS

    Hepatitis B & C causes worldwide morbidity and mortility. Antiviral drugs do not cure the condition, their role is suppressive only. Thus search for curative agent is continued.

  A number of agents are available for treatment of hepatitis B virus (HBV) and Hepatitis C virus (HCV) infections.

Drugs:1. Interferons
           2. Ribavirin
           3. Nucleoside/Nucleotide Analogs
                        A-Lamivudine
                        B-Telbivudine
                        C-Adefovir dipivoxil
           They have other uses as well.

Review of Drugs:
   1. Interferons - Iterferons are proteins produced by virus infected cells and also by recombinant DNA technology. They are mainly 3 types of Interferons : Alpha, Beta & Gamma. Two pegylated  Interferons are available commercially.
Attachment of IFN proteins to large inert polyethylene glycol(PEG) molecules.
Pegylation slows absorption decreases clearance and provides higher and more prolonged serum concentrations,that enables once weekly dosing.
Pegyinterferons alfa 2a(PEGASYS) and Pegyinterferons alfa 2b (PEG-INTRON).
 Antiviral activity of interferons is due to inhibition of viral penetration, uncoating, synthesis of mRNA, translation of viral protein, assembly of viral particles and their release.They are administered by IM,SC routes.
              Adverse effects - fever, headache, myalgia, skin rases, alopecia, bone marrow suppression and thyroid disfunction.

2. Ribavirin - It is guanine analogue, it is RNA dependent RNA polymerase inhibitor. It is administered by oral aerosol or IV routes.It is effective against a range of RNA & DNA viruses.
                Adult dose - po 1.2 gm to 2.4 gm every 8 hourly .
                Adverse effects - Nausea, vomiting, malaise, cough, insomnia,and anemia.
                Contraindication - Pregnancy, female of child bearing age.

3. Nucleoside/Nucleotide Analogs -
    A-Lamivudine(3TC) - It is a synthetic cytosine analogue. oral bio availability 80%,food does not interfere its absorption pt1/2 12 hour.
And more prolonged in HBV and HIV and used 100 mg once a day. Its suppresses HBV DNA more rapidly than Interferons. It is often used with Interferon Alfa for HBV infection.      
              Adverse effect-It is best tolerated and least toxic. GIupsets, headache, insomnia, myositis, hepatitis, anemia, pancreatitis, granulocytopenia.
     
   B-Adefovir dipivoxil - It is adenosine analogue developed for the treatment of HIV but is also effective for HBV infection in doses lower than HIV.
Mechanism of Action-It is converted to active diphosphate metabolite by cellular kinases and is incorporated in viral DNA and causes chain termination by inhibiting HBV DNA polymerase.

 ADME-Its oral bioavailability is 60% .It is eliminated unchanged through kidneys. Its intracellular plasma half life ranges from 5-18 hours.
 Adverse effects- It causes dose dependent nephrotoxicity and in patient with pre existing renal disease, Hepatomegaly and Lactic acidosis may occur. 

Clinical Uses:
     1. Chronic Hepatitis-B : Interferon alfa-2b 5 MU OD or 10 MU three times per week or (Interferon alfa-2b 2.5-5 MU/meter square) IM SC lead to loss of Hepatitis-B antigen, aminotransferase level comes to normal and sustained improvement occurs histological. Pegylated IFN Alfa-2a 180 mcg once a week, SC for 24-48 weeks is more effective.
       

  2. Acute Hepatitis-C : Interferon alfa-2b 5 MU OD for 3 weeks and then 5 MU 3 times weekly SC/IM.

  3. Chronic Hepatitis-C : Both IFN alfa-2a or Interferon alfa-2b in a dose of 3 MU three times per week SC/IM for 6-12 months produce remission in 50-70% patients . Pegylated IFN Alfa-2a (180 mcg once a week, SC for 48 weeks) or Pegylated IFN Alfa-2b (50-150 mcg) once a week, SC for 48 weeks. Response is further improved with Ribavirin 800-1200 mg OD orally.
Maximum response in all the cases of Chronic Hepatitis-C occurs in 6-12 months of continuous treatment. 


    Dr. P.S SINGH
    PROFESSOR & H.O.D
    PHARMACOLOGY
    SANTOSH MEDICAL COLLEGE
    GHAZIABAD