How is Hepamerz (hepatitis B immune globulin) indicated and dosed for post‑exposure prophylaxis in newborns of hepatitis B surface antigen‑positive mothers and in exposed adults or children?

Hepamerz (Hepatitis B Immune Globulin) Indications and Dosing

Newborns of HBsAg-Positive Mothers

Administer 0.5 mL HBIG intramuscularly within 12 hours of birth into the anterolateral thigh, simultaneously with the first hepatitis B vaccine dose at a separate anatomic site. 1, 2, 3

Critical Timing Considerations

• Efficacy is 85-95% when both HBIG and vaccine are given within 12 hours of birth to prevent acute and chronic HBV infection in infants born to HBsAg/HBeAg-positive mothers. 4, 2
• HBIG may provide some protection up to 72 hours after birth, but efficacy decreases markedly after 48 hours. 4, 3
• Do not delay beyond 12 hours—this is the single most important factor determining prophylaxis success. 1, 2

Vaccine Series Completion

• Complete a 3-dose vaccine series at birth, 1-2 months, and 6 months of age. 4
• For preterm infants weighing <2,000 grams: the birth dose does not count toward the series; administer 4 total doses (birth plus 3 additional doses starting at 1 month). 2

Post-Vaccination Testing

• Test for anti-HBs and HBsAg at 9-12 months of age (typically at the next well-child visit after completing the vaccine series) to identify prophylaxis failures. 2
• Infants with anti-HBs ≥10 mIU/mL and negative HBsAg are protected and require no further management. 2

Alternative Scenarios

• If vaccine is refused or delayed beyond 3 months: repeat the 0.5 mL HBIG dose at 3 months and again at 6 months. 3
• If the first vaccine dose is delayed up to 3 months, give an additional 0.5 mL HBIG dose at 3 months. 3

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Adults and Children: Percutaneous/Mucosal Exposure

Administer HBIG 0.06 mL/kg intramuscularly (approximately 3,000-5,000 IU for adults) as soon as possible, preferably within 24 hours of exposure, into the deltoid muscle. 1, 3

Timing Windows

• Effectiveness declines markedly after 7 days for needlestick and percutaneous exposures. 4, 1
• Maximum single injection volume should not exceed 5 mL, even for large individuals. 1

Management Based on Vaccination Status

Unvaccinated or Unknown Immunity:

• Give HBIG 0.06 mL/kg immediately and initiate the hepatitis B vaccine series simultaneously at a separate site. 1, 3

Vaccinated with Unknown Anti-HBs Status:

• Provide HBIG 0.06 mL/kg plus a hepatitis B vaccine booster at a different anatomic site. 1, 3

Known Vaccine Non-Responders:

• Administer HBIG 0.06 mL/kg immediately, with consideration of either a second HBIG dose one month later OR HBIG combined with a new three-dose vaccine series. 1, 3

Documented Immunity (anti-HBs ≥10 mIU/mL):

• No HBIG required regardless of exposure type. 1

Important Caveats

• Do not wait for serologic test results before administering HBIG in high-risk exposures—immediate prophylaxis takes priority. 1
• Combined passive-active prophylaxis with HBIG and vaccine is more effective than HBIG alone for preventing transmission after HBV exposure. 4, 5

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Sexual Exposure to HBsAg-Positive Person

Administer HBIG 0.06 mL/kg as a single intramuscular dose within 14 days of the last sexual contact, and start the hepatitis B vaccine series simultaneously at a separate site. 1, 3

• The effectiveness window extends to 14 days for sexual exposures, longer than the 7-day window for percutaneous exposures. 4, 1
• Administering vaccine with HBIG improves efficacy and provides long-lasting protection. 3

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Household Exposure

For infants <12 months exposed to a primary caregiver with acute hepatitis B:

• Administer 0.5 mL HBIG plus hepatitis B vaccine. 3

For other household contacts:

• Prophylaxis is not indicated unless they have identifiable blood exposure (e.g., sharing toothbrushes or razors)—treat these as sexual exposures. 3
• If the index patient becomes an HBV carrier, vaccinate all household contacts without HBIG. 3

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Post-Administration Testing Considerations

• Passive anti-HBs from HBIG persists for 4-6 months; postpone anti-HBs testing until 4-6 months after HBIG administration to avoid false-positive results. 4, 1
• HBIG may be administered up to 1 month before hepatitis B vaccination without impairing the active immune response. 3

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Common Pitfalls to Avoid

• Delaying HBIG administration in newborns beyond 12 hours dramatically reduces efficacy—this is the most critical error. 1, 2
• Failing to administer vaccine simultaneously with HBIG at a separate site reduces long-term protection. 1, 2, 3
• Skipping post-vaccination testing at 9-12 months in newborns prevents identification of prophylaxis failures. 2
• Administering HBIG intravenously instead of intramuscularly (except in liver transplant settings). 3
• Using standard adult vaccine doses in hemodialysis patients—these individuals require higher doses (40 µg formulation) for adequate response. 1