How should hepatitis B immune globulin (HBIG) be dosed in international units for post‑exposure prophylaxis in adults and infants, and for high‑risk exposure or liver transplantation?

Hepatitis B Immunoglobulin Dosing in International Units

For post-exposure prophylaxis in adults and infants, administer HBIG at 0.06 mL/kg body weight intramuscularly, which corresponds to approximately 3,000-5,000 IU for adults and 100-200 IU for newborns, given as soon as possible (preferably within 24 hours). 1

Standard Post-Exposure Prophylaxis Dosing

Adults and Older Children

• Administer 0.06 mL/kg body weight intramuscularly for percutaneous, mucosal, or sexual exposure to HBsAg-positive sources 1, 2
• For a typical 70 kg adult, this translates to approximately 4.2 mL or roughly 3,000-5,000 IU 1
• Maximum single injection volume is limited to 5 mL for very large adults, despite weight-based calculations 1
• Inject into the deltoid muscle for optimal absorption 1
• Effectiveness declines markedly after 7 days for percutaneous exposures and after 14 days for sexual exposures 1, 2

Newborns and Infants (Perinatal Exposure)

• Administer 0.5 mL (approximately 100-200 IU) intramuscularly within 12 hours of birth for infants born to HBsAg-positive mothers 2
• A prospective cohort study demonstrated that 100 IU HBIG combined with hepatitis B vaccine was equally effective as 200 IU in preventing mother-to-child transmission (1.5% vs 1.9% infection rates, p=0.568) 3
• Inject into the anterolateral thigh for neonates 2
• Always administer simultaneously with the first dose of hepatitis B vaccine at a separate anatomic site 1, 2

High-Risk Exposure Scenarios

Occupational Needlestick Injuries

• Give HBIG 0.06 mL/kg immediately when the source is HBsAg-positive and the exposed person is unvaccinated or has unknown immunity 1
• For vaccinated persons with unknown anti-HBs status exposed to HBsAg-positive sources, administer HBIG 0.06 mL/kg plus a vaccine booster at a separate site 1
• Known vaccine non-responders require 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

Sexual Exposure

• Administer HBIG 0.06 mL/kg as a single dose within 14 days of last sexual contact with an HBsAg-positive person 2
• Start the hepatitis B vaccine series simultaneously at a different injection site 2

Liver Transplantation Dosing

Intraoperative and Early Post-Transplant Period

• Administer 10,000 IU intravenously during the anhepatic phase 4
• Follow with 600-1,000 IU intramuscularly or intravenously daily for 7 days 4
• Then weekly for 3 weeks 4
• Then monthly until month 3-6 4

Long-Term Maintenance After Transplantation

• After 6 months post-transplant, dose HBIG to maintain anti-HBs serum levels >100 mIU/mL 4
• Combine with a high genetic barrier nucleos(t)ide analogue indefinitely 4
• The optimal HBIG dose varies among centers and should be individualized based on anti-HBs monitoring 4

Critical Timing Considerations

HBIG must be administered as soon as possible after exposure—preferably within 24 hours—because efficacy decreases substantially with delays. 1, 2

• For percutaneous exposures: effectiveness declines markedly after 7 days 1
• For sexual exposures: the window extends to 14 days but earlier is better 1, 2
• For perinatal exposures: administration within 12 hours of birth is critical for optimal protection 2

Coordination with Hepatitis B Vaccine

Always administer HBIG and hepatitis B vaccine simultaneously at separate anatomic sites when both are indicated. 1, 2

• The vaccine series should be completed even after HBIG administration 1
• Do not delay HBIG while waiting for serologic test results in high-risk exposures, as the risk of not treating someone who lacks immunity outweighs the cost of treating someone who may already be protected 1

Post-Administration Testing Considerations

• Delay post-vaccination anti-HBs testing until 4-6 months after HBIG administration to avoid detecting passively transferred antibodies 1, 2
• HBIG provides passively acquired anti-HBs that can be detected for 4-6 months 4
• If HBIG was not given, test anti-HBs 1-2 months after completing the vaccine series 1

Common Pitfalls to Avoid

• Never wait for serologic test results before administering HBIG in high-risk exposures—immediate prophylaxis takes priority 1
• Do not assume immunity without documented anti-HBs ≥10 mIU/mL—vaccination history alone is insufficient 1
• Persons with documented immunity (anti-HBs ≥10 mIU/mL) do not require HBIG regardless of exposure type 1
• Do not test for anti-HBs immediately after HBIG administration—wait 4-6 months to avoid false-positive results from passive antibodies 1, 2
• Do not use standard adult doses in hemodialysis patients—they require higher doses (40 μg vaccine formulation) for adequate response 5