Mechanism of Action

HBIGIV products provide passive immunization for individuals exposed to the hepatitis B virus, by binding to the surface antigen and reducing the rate of hepatitis B infection^13-16.

Hepatitis B virus reinfection following liver transplantation is the consequence of exposure of the new liver graft to hepatitis B virus. Reinfection may occur immediately at the time of liver reperfusion due to circulating virus or later from virus retained in extrahepatic sites.

The mechanism whereby hepatitis B Immune globulin (HBIG) protects the transplanted liver against HBV reinfection is not well understood. HBIG may protect naive hepatocytes against infection through blockage of a putative HBV receptor¹⁷. Alternatively, HBIG may neutralize circulating virions through immune precipitation and immune complex formation or may trigger an antibody-dependent cell-mediated cytotoxicity response resulting in target cell lysis^{17, 18}. In addition, HBIG has been reported to bind to hepatocytes and interact with HBsAg within cells¹⁹. Regardless of the mechanism, there is evidence of a dose-dependent response to HBIG treatment^5,8.

Postexposure Prophylaxis

Clinical studies conducted prior to 1983 with hepatitis B immune globulins similar to HepaGam B demonstrated the advantage of simultaneous administration of hepatitis B vaccine and Hepatitis B Immune Globulin (Human), by the i.m. route. The Centers for Disease Control and Prevention Advisory Committee on Immunization Practices (ACIP) advises that the combination prophylaxis be provided following certain instances of hepatitis B exposure.^1,2 Recommendations on post-exposure prophylaxis are based on available efficacy data, primarily from studies in neonates^1,2. Cases of hepatitis B are rarely seen following exposure to HBV in persons with pre-existing anti-HBs antibodies.

Infants born to HBsAg-positive mothers are at risk of being infected with HBV and becoming chronic carriers¹. The risk is especially great if the mother is also HBeAg-positive¹. For an infant with perinatal exposure to an HBsAg-positive and HBeAg-positive mother, a regimen combining one dose of Hepatitis B Immune Globulin (Human) at birth with the hepatitis B vaccine series started soon after birth has been shown to be 85-98% effective in preventing development of the HBV carrier state^1,2. Regimens involving either multiple doses of Hepatitis B Immune Globulin (Human) alone or the vaccine series alone have a 70-75% efficacy, while a single dose of Hepatitis B Immune Globulin (Human) alone has 50% efficacy^1,2.

Since infants have close contact with primary caregivers and have a higher risk of becoming HBV carriers after acute HBV infection, prophylaxis of an infant less than 12 months of age with Hepatitis B Immune Globulin (Human) and Hepatitis B Vaccine is indicated if the mother or primary caregiver has acute HBV infection¹.

Sexual partners of HBsAg-positive persons are at increased risk of acquiring HBV infection. A single dose of Hepatitis B immune Globulin (Human) is 75% effective if administered within two weeks of the last sexual exposure to a person with acute hepatitis B^1,2.

HBV infection is a well-recognized risk to health- care personnel (HCP). The risk of HBV infection is primarily related to the degree of contact with blood in the work place and also to the hepatitis B e antigen (HBeAg) status of the source person. In studies of HCP who sustained injuries from needles contaminated with blood containing HBV, the risk of developing clinical hepatitis if the blood was hepatitis B surface antigen (HBsAg) and HBeAg-positive was 22%-31%; the risk of developing serologic evidence of HBV infection was 37%-62%. In comparison, the risk of developing clinical hepatitis from needles contaminated with HBsAg-positive, HBeAg- negative blood is 1%-6%, and the risk of developing serological evidence of HBV infection is 23%-37%²⁰. The current recommendations of the Advisory Committee on Immunization Practices^1,2, recommends postexposure prophylaxis with hepatitis B immune globulin and/or hepatitis B vaccine series for any susceptible, unvaccinated person who sustains an occupational blood or body fluid exposure.

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