Rhogam is often administered to D-negative women during pregnancy to reduce the chances of becoming alloimmunized. The level of antibody can persist for several weeks and may be rarely detected up to 6 months after administration.


Factors affecting duration of effect:

(1) total dose administered

(2) bleeding or increased rate of loss

(3) number of D-positive cells to bind to


Assuming first order kinetics (a simplification):


concentration at time T in ng/mL =

= (maximum concentration in ng/mL) * EXP((-1) * 0.693 / (half life in days) * (T days since administration))


percent remaining =

= 100% * EXP((-1) * 0.693 / (half life in days) * (T days since administration))


Values from Package Insert

after 300 µg (1 vial)

after 1,200 µg (4 vials)

maximum concentration

37.1 ng/mL

146.3 ng/mL

half-life in days



volume of distribution

8.59 liters

8.16 liters



• The kinetic data is based on 6 patients with 1 dose and 2 patients with 4 doses.

• The route of administration was intramuscular (IM).

• The peak concentration on 4 doses was 36.5 ng/mL per dose.


Based on this data, I have used the following data for half-life in the implementation, which has not been validated.


Number of Vials

half-life in days










According to the AABB Technical Manual, the half life of Rhogam is 21 days in the absence of significant fetomaternal hemorrhage. If a singled 300 µg dose is administered at 28 weeks of gestation, then 7-10% (20-30 µg) should remain at 40 weeks of gestation.


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