Anti-D Content in RhIg (Rhogam) 1mL Vial
A standard 1mL vial of RhIg (Rhogam) contains 300 mcg (1500 IU) of anti-D immunoglobulin. 1
Composition and Potency Details
The FDA-approved product information for Rho(D) Immune Globulin (Human) confirms that each single-dose syringe contains:
- 300 mcg (1500 IU) of anti-D immunoglobulin
- Formulated as a 15-18% protein solution
- pH of 6.4-7.2 in 0.21-0.32 M glycine
- Preservative-free solution
This standard dose is sufficient to effectively suppress the immunizing potential of 15 mL of Rho(D) positive red blood cells 1.
Clinical Applications
The dosing of RhIg is based on the volume of potential fetal-maternal hemorrhage:
Standard full dose (300 mcg/1500 IU): Used for:
- Postpartum prophylaxis after delivery of an Rh-positive infant
- Antenatal prophylaxis at 28 weeks gestation
- Events after 12 weeks gestation that risk fetal-maternal hemorrhage
Microdose (50 mcg): Used for early pregnancy events before 12 weeks gestation 2
Mechanism and Duration of Protection
When administered, the 300 mcg dose provides:
- Protection against alloimmunization from up to 15 mL of Rh-positive red blood cells
- Effective prevention when given within 72 hours of potential exposure to Rh-positive blood
- Detectable anti-D levels for approximately 75 days in most women 3
Important Clinical Considerations
Duration of protection: Studies show that after standard 300 mcg dose administration:
- 54% of women have detectable anti-D at delivery if they deliver within 75 days of administration
- Only 2.4% have detectable anti-D if delivery occurs 76-95 days after administration
- No detectable anti-D beyond 96 days after administration 3
Efficacy: A single 300 mcg dose provides approximately 96% protection against Rh sensitization when used in a comprehensive prophylaxis program 4
Additional dosing: For large fetomaternal hemorrhages exceeding 15 mL of fetal red blood cells, additional anti-D may be required at a rate of 10 mcg for every additional 0.5 mL of fetal red blood cells 5
Administration route: The 300 mcg dose can be administered either intramuscularly or intravenously with equal effectiveness, though the pharmacokinetics differ slightly in the first week 6
Remember that proper dosing and timing of RhIg administration is critical for preventing Rh alloimmunization, which can lead to significant morbidity and mortality through hemolytic disease of the fetus and newborn in subsequent pregnancies.