Rh_o(D) Immune Globulin (RhIG)

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 Action By binding Rh_o(D) antigen on red blood cells (RBCs), RhIG prevents production of anti-Rh_o(D) antibodies in Rh_o(D) antigen-negative people. Prevention of Rh sensitization, in turn, prevents hemolytic disease of fetus and newborn in subsequent Rh_o(D) antigen-positive children.

 Indications Passive, transient protection against development of endogenous anti-Rh antibodies (isoimmunization) in nonsensitized Rh antigen-negative persons who receive Rh antigen-positive blood. Such exposure may result from fetomaternal hemorrhage occurring during delivery, spontaneous or induced abortion, abdominal trauma, ectopic pregnancy, chorionic villus sampling (CVS), percutaneous umbilical cord blood sampling (PUBS), amniocentesis, fetal surgery or manipulation, or as result of transfusion accident. RhIG prevents hemolytic disease of fetus and newborn (including erythroblastosis fetalis and hydrops fetalis) in subsequent Rh antigen-positive children. If Rh typing of fetus is not possible, assume fetus is Rh antigen-positive and give mother RhIG. Do not perform Rh cross-match prior to administration.

Term delivery: To warrant RhIG administration, (1) mother must be Rh antigen-negative, (2) mother should not have been previously sensitized to Rh factor (and thus produce her own anti-Rh antibodies), and (3) infant must be Rh antigen-positive and direct antiglobulin negative. (4) If father can be determined to be Rh antigen-negative, RhIG need not be given. Other obstetric conditions: Administer RhIG to all nonsensitized Rh antigen-negative women after spontaneous or induced abortions, after ruptured ectopic pregnancies, amniocentesis, other abdominal trauma, CVS, PUBS, fetal surgery or manipulation, or any transplacental hemorrhage, unless blood type of fetus has been determined to be Rh antigen-negative. Sensitization occurs more frequently in women undergoing induced abortions than in those aborting spontaneously. Transfusion accidents: RhIG can be used to prevent Rh sensitization in Rh antigen-negative patients who accidentally receive transfusions with RBCs or blood components containing RBCs, platelets, or granulocytes prepared from Rh antigen-positive blood. Administer within 72 hr following Rh-incompatible transfusion.

 Contraindications Hypersensitivity to thimerosal, any immune globulin, or any of the product's components. MICRhoGAM Any indication with continuation of pregnancy or beyond 12 wk gestation.

 Route/Dosage

For IM administration only. Contents of total dose may be injected as divided dose at different injection sites at same time, or total dosage may be divided and injected at intervals, provided total dosage to be given is injected within 72 hr.

Postpartum Prophylaxis, Miscarriage, Abortion, or Ectopic Pregnancy

1 full-dose vial or syringe of RhIG prevents maternal sensitization if RBC volume that entered mother's circulation is < 15 mL. When fetomaternal hemorrhage exceeds 15 mL of RBCs, administer ³ 1 container of RhIG. One minidose container of RhIG will prevent formation of anti-Rh antibodies resulting from spontaneous or induced abortion up to 12 wk gestation. After 12 wk gestation, give full-dose container.

Antepartum Prophylaxis

1 full-dose container of RhIG at 28 wk gestation and again within 72 hr after Rh-incompatible delivery is highly effective in preventing Rh isoimmunization during pregnancy.

Threatened Abortion

Following threatened abortion at any stage of gestation with continuation of pregnancy, give 1 full-dose container of RhIG, unless larger dose is needed.

Amniocentesis or Abdominal Trauma

Following amniocentesis at either 15 to 18 wk gestation or during third trimester, or following abdominal trauma in second or third trimester, give 1 full-dose container of RhIG, unless larger dose is needed.

Transfusion Accidents

Dose of RhIG is dependent on volume of red cells or whole blood transfused. To determine amount of RhIG needed, multiply volume (measured in mL) of Rh antigen-positive whole blood administered by Hct of donor unit. This value equals volume of RBCs transfused. Divide volume of RBCs by 15 to obtain dose of RhIG needed. If dose calculation results in fraction, administer next higher whole number of full-dose vials or syringes of RhIG. Rh antigen-negative patients who receive Rh antigen-positive blood have received as many as 15 to 33 vials of RhIG without adverse reaction. If any event requires administration of RhIG at 13 to 18 wk gestation, give another full dose at 26 to 28 wk gestation. Give additional full dose of RhIG within 72 hr after delivery if infant is Rh antigen-positive. If delivery occurs within 3 wk after last dose, postpartum dose may be withheld, unless there is fetomaternal hemorrhage of > 15 mL RBCs.

 Interactions Antibodies in RhIG may interfere with response to live vaccines. Do not give live vaccines within 14 to 30 days before or 3 mo after RhIG administration. Nonetheless, RhIG does not usually impair response to rubella vaccine. Rubella-susceptible postpartum women who received blood products or RhIG may receive rubella vaccine prior to discharge, provided that rubella antibody titer is drawn 6 to 8 wk after vaccination to ensure seroconversion.

 Lab Test Interferences Infants born of women given RhIG antepartum may have weakly positive antiglobulin (Coombs') test result at birth. Anti-Rh antibodies may be detected in maternal serum within several wk of administration of RhIG. Such finding does not preclude further RhIG doses. Presence of RhIG antibodies in maternal blood sample can affect interpretation of tests to identify patient as candidate for RhIG. In case of doubt as to patient's Rh group or immune status, give RhIG. Significant fetomaternal hemorrhage late in pregnancy or following delivery may cause weak, mixed-field positive D^u test result. If there is any doubt about mother's Rh type, give RhIG. Screening test for fetal RBCs may help in such cases.

 Adverse Reactions

OTHER: As with most IgG products, adverse reactions are infrequent, usually mild in nature and generally confined to site of injection. Occasional patient may react more strongly with localized tenderness, erythema, or low-grade fever. Fever, splenomegaly, myalgia, lethargy, and elevated bilirubin levels occur in some individuals receiving multiple doses of RhIG following mismatched transfusions. This latter reaction may be due to relatively rapid rate of foreign red cell destruction, not to RhIG. Hypersensitivity and systemic reactions and induced sensitization with repeated injections occur rarely.

 Precautions

Pregnancy: Category C. Lactation: Undetermined. Children: For suppression of Rh isoimmunization in the mother. Do not administer to infants. IM administration: As with other drugs administered by IM injection, give RhIG with caution to patients on anticoagulant therapy.

 Administration/Storage

• Administer IM only.
• If desirable, divide total dose and give at different injection sites or inject at intervals.
• Give total dosage within 72 hr.
• Store in refrigerator.
• Confirm mother is Rh_o(D) negative prior to administration.
• Obtain blood type and direct antiglobulin test on infant immediately postpartum, prior to administration.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Observe injection site for tenderness or erythema.
• Administer with caution if patient is receiving anticoagulants.
• Notify physician if fever, splenomegaly, myalgia, or lethargy develop.
• Assess bilirubin levels prior to and following treatment.

 Patient/Family Education

• Tell patient to report fever, myalgia, lethargy, abdominal pain, or jaundice to physician.
• Instruct patient not to receive any live vaccines within 30 days before or 3 mo after administration of drug.
• Explain how future Rh_o-positive infants will be protected.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts