Nabi-HB (Hepatitis B Immune Globulin (Human)) - Description and Clinical Pharmacology

DESCRIPTION

Hepatitis B Immune Globulin (Human), Nabi-HB, is a sterile solution of immunoglobulin (5 ± 1% protein) containing antibodies to hepatitis B surface antigen (anti-HBs). It is prepared from plasma donated by individuals with high titers of anti-HBs. The plasma is processed using a modified Cohn 6 / Oncley 9 cold-alcohol fractionation process^1,2 with two added viral reduction steps described below. Nabi-HB is formulated in 0.075 M sodium chloride, 0.15 M glycine, and 0.01% polysorbate 80, at pH 6.2. The product is supplied as a nonturbid sterile liquid in single dose vials and appears as clear to opalescent. It contains no preservative and is intended for single use by the intramuscular route only.

The manufacturing steps for Nabi-HB are designed to reduce the risk of transmission of viral disease. The solvent/detergent treatment step, using tri- n -butyl phosphate and Triton® X-100, is effective in inactivating known enveloped viruses such as hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) ³. Virus filtration, using a Planova® 35 nm Virus Filter, is effective in reducing some known enveloped and non-enveloped viruses⁴. The inactivation and reduction of known enveloped and non-enveloped model viruses were validated in laboratory studies as summarized in the following table:

Product potency is expressed in international units (IU) by comparison to the World Health Organization (WHO) standard. Each milliliter (mL) of product contains greater than 312 IU anti-HBs. The potency of each milliliter of Nabi-HB exceeds the potency of anti-HBs in a U.S. reference hepatitis B immune globulin (FDA). The U.S. reference has been tested by Nabi® Biopharmaceuticals against the WHO standard and found to be equal to 208 IU/mL.

CLINICAL PHARMACOLOGY

Hepatitis B Immune Globulin (Human) products provide passive immunization for individuals exposed to the hepatitis B virus as evidenced by a reduction in the attack rate of hepatitis B following use^6-9.

Clinical studies^10,11 conducted prior to 1983 with hepatitis B immune globulins similar to Nabi-HB indicate the advantage of simultaneous administration of hepatitis B vaccine and Hepatitis B Immune Globulin (Human). The Centers for Disease Control and Prevention Advisory Committee on Immunization Practices (ACIP) advises that the combination prophylaxis be provided in certain instances of exposure based upon the increased efficacy found with that regimen in neonates¹². Cases of hepatitis B are rarely seen following exposure to HBV in persons with preexisting anti-HBs. However, no prospective studies have been performed on the efficacy of concurrent hepatitis B vaccine and Hepatitis B Immune Globulin (Human) administration following parenteral exposure, mucous membrane contact, or oral ingestion in adults.

Infants born to HBsAg-positive mothers are at risk of being infected with HBV and becoming chronic carriers¹³. The risk is especially great if the mother is also HBeAg-positive¹⁴. Studies conducted with hepatitis B immune globulins similar to Nabi-HB indicated that 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 is 85-98% effective in preventing development of the HBV carrier state^15-17. Regimens involving either multiple doses of Hepatitis B Immune Globulin (Human) alone or the vaccine series alone have a 70-90% efficacy, while a single dose of Hepatitis B Immune Globulin (Human) alone has 50% efficacy¹⁸.

Since infants have close contact with primary caregivers and they 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 infection¹⁹.

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 B¹⁹.

PHARMACOKINETICS

Pharmacokinetics trials²⁰ of Nabi-HB, Hepatitis B Immune Globulin (Human), given intramuscularly to 50 healthy volunteers demonstrated pharmacokinetic parameters similar to those reported by Scheiermann and Kuwert²¹. The half-life for Nabi-HB was 23.1 ± 5.5 days. The clearance rate was 0.35 ± 0.12 L/day and the volume of distribution was 11.2 ± 3.4 L.

Maximum concentration of Nabi-HB was reached in 6.5 ± 4.3 days. The maximum concentration of anti-HBs and the area under the time-concentration curve achieved by Nabi-HB were bioequivalent to that of another licensed Hepatitis B Immune Globulin (Human) when compared in the same pharmacokinetics trial. Comparability of pharmacokinetics between Nabi-HB and a commercially available hepatitis B immunoglobulin indicate that similar efficacy of Nabi-HB should be inferred.