New IV Rh-IgG takes aim at pregnant women

The Food & Drug Administration recently approved Rho(D) Immune Globulin Intravenous (Rhophylac, ZLB Bioplasma) for prevention of rhesus incompatibility. Rhophylac, which has been available in Europe since 1996, offers the flexibility of intravenous or intramuscular administration.

The rhesus (Rh) factor is a protein located on the surface of red blood cells in some individuals. Those who have this Rh factor are considered Rh-positive; those who do not, Rh-negative. Rhesus incompatibility, a devastating hemolytic disorder, occurs only in the Rh-positive fetuses of Rh-negative mothers. It is caused by leakage of fetal red blood cells into the maternal bloodstream. Fetal red blood cells naturally cross the placenta during delivery, miscarriage, or abortion. They can also leak during traumatic events and procedures, including ectopic pregnancy, abruptio placentae, chorionic villus sampling, amniocentesis, and external cephalic version.

When Rh-positive fetal red blood cells cross the placenta, maternal sensitization occurs, inducing an immunologic response. The initial maternal response is the production of IgM, followed by production of IgG. Although the IgM molecule is too large to cross the placenta, the IgG molecule can cross the placenta, entering the fetal circulation. Once that happens, hemolysis occurs, leading to profound anemia, cardiomegaly, pleural effusions, ascites, even death.

During an uncomplicated pregnancy, the first maternal exposure to fetal blood typically occurs during delivery. Since the mother's immune system will not immediately produce anti-Rh IgG, the soon-to-be-born child is at minimal risk. Unfortunately, any subsequent pregnancy with an Rh-positive fetus will increase the maternal immunologic response, causing a more severe antibody attack on the fetus. Sometimes the mother is exposed to fetal blood prior to delivery, usually due to testing or obstetric complications. In contrast with blood transfer during delivery, when the mother is exposed to fetal blood earlier in the pregnancy, the current fetus is at risk for antibody attack.

To prevent the production of antibodies, Rho(D) immune globulin is administered to nonsensitized Rh-negative women—300 mcg of Rh immune globulin at 28 to 30 weeks of gestation—carrying a baby that is either Rh-positive or Rh-unknown and whose father is Rh-positive or Rh-unknown. The Rh immune globulin will destroy any fetal red blood cells that have entered the maternal bloodstream, preventing the formation of maternal antibodies to the Rh factor. Another dose is administered within 72 hours after delivery if the baby is Rh-positive. The mother must receive immune globulin injections during each pregnancy.

Until recently, the Rh immune globulin products available in the United States were approved only for intramuscular administration, causing local pain and tenderness at the injection site. Rhophylac, available in prefilled latex-free syringes containing 300 mcg of thimerosol-free and mercury-free immune globulin, now offers flexibility in administration route. Mothers will appreciate the new choice of intravenous administration since it causes less discomfort, particularly when multiple injections are necessary. Rhophylac can also be injected intramuscularly, the more convenient route of administration in the physician's office.

Intravenous administration of Rhophylac is possible because of the extensive purification process utilized, including removal of most viruses and IgA. The manufacturer utilizes solvent/detergent treatment and nanofiltration to remove viruses, including SARS, HIV, and hepatitis.

Rhophylac is indicated for routine antepartum and postpartum prevention of Rh immunization in Rh-negative women and for rhesus prophylaxis in cases of obstetric complications or invasive procedures during pregnancy. It is also indicated for the suppression of rhesus immunization in Rh-negative individuals transfused with Rh-positive red blood cells or blood components.

TIPS TO REMEMBER: Rhophylac

• Rhophylac can be administered intravenously or intramuscularly.

• Rhophylac is contraindicated in persons with hypersensitivity to human globulin. Since it contains small amounts of IgA, persons with IgA deficiency have an increased risk of antibody production and anaphylactic reactions.

• All patients should be observed for hypersensitivity reactions for 20 minutes after administration.

• Rhophylac should be administered within 72 hours of delivery, miscarriage, abortion, or other obstetric complications.

• Rhophylac should be administered to the Rh-negative mother only, not to the newborn.

• Immunization with live virus vaccines within three months of immune globulin administration may reduce the efficacy of the vaccine.