Rhogam Ultra-Filtered Plus (Rho(d) Immune Globulin Human) - Description and Clinical Pharmacology

DESCRIPTION

RhoGAM and MICRhoGAM Rh_o(D) Immune Globulin (Human) are sterile solutions containing immunoglobulin G (IgG) anti-D (anti-Rh) for use in preventing Rh immunization. They are manufactured from human plasma containing anti-D. A single dose of RhoGAM contains sufficient anti-D (300 μg or 1500 IU) to suppress the immune response to up to 15 mL of Rh-positive red blood cells.^4,15 A single dose of MICRhoGAM contains sufficient anti-D (50 μg or 250 IU) to suppress the immune response to up to 2.5 mL of Rh-positive red blood cells. The anti-D dose is measured by comparison to the RhoGAM in-house reference standard, the potency of which is established relative to the U.S./World Health Organization/European Pharmacopoeia Standard Anti-D Immunoglobulin Rh_o(D) Immune Globulin (Human) CBER Lot 4: NIBSC Lot 01/572 (285 IU/ampoule).¹⁶

Plasma for RhoGAM is typically sourced from a donor center owned and operated by Ortho-Clinical Diagnostics. All donors are carefully screened by history and laboratory testing to reduce the risk of transmitting blood-borne pathogens from infected donors. Each plasma donation is tested and found to be non-reactive for the presence of hepatitis B surface antigen (HBsAg) and antibodies to hepatitis C (HCV) and human immunodeficiency viruses (HIV) 1 and 2. Additionally, plasma is tested by FDA licensed Nucleic Acid Testing (NAT) for HCV and HIV-1 and the results must be negative. Plasma is also tested by investigational NAT for hepatitis B (HBV) and must be non-reactive. However, the significance of a negative result has not been established. Plasma is tested by in-process NAT procedures for hepatitis A virus (HAV) and parvovirus B19 (B19) in a minipool format. Only plasma that has passed virus screening is used for production. The procedure for B19 detects all three genotypes based upon sequence alignment of known virus isolates. The limit of B19 DNA in the manufacturing pool is set not to exceed 10⁴ IU per mL.

Fractionation of the plasma is performed by a modification of the cold alcohol procedure that has been shown to significantly lower viral titers.¹⁰ Following plasma fractionation, a viral clearance filtration step and a viral inactivation step are performed. The viral filtration step removes viruses via a size-exclusion mechanism utilizing a patented Viresolve 180 ultrafiltration membrane with defined pore-size distribution of 12-18 nanometers to remove enveloped and non-enveloped viruses. Following viral filtration, quality control tests (CorrTest and diffusion test) are performed on the Viresolve 180 ultrafiltration membrane to insure filter integrity.¹⁷ The viral inactivation step utilizes Triton X-100 and tri-n-butyl phosphate (TNBP) to inactivate enveloped viruses such as HCV, HIV and West Nile Virus (WNV)^10,18 (Patent Pending).

The donor selection process, the fractionation process, the viral filtration step and the viral inactivation process increase product safety by reducing the risk of transmission of enveloped and non-enveloped viruses. Rh_o(D) Immune Globulin (Human) intended for intramuscular use and prepared by cold alcohol fractionation has not been shown to transmit hepatitis or other infectious diseases.¹⁹ There have been no documented cases of infectious disease transmission by RhoGAM or MICRhoGAM.

Laboratory spiking studies^10,20 have shown that the cumulative viral removal and inactivation capability of the RhoGAM / MICRhoGAM manufacturing process is as follows:

Virus	HIV	BVDV	PRV	PPV	EMC	WNV	HAV
Units = log10 reduction HIV Human Immunodeficiency Virus, Model for HIV-1 and 2 and Human T-cell Lymphotropic Virus (HTLV) 1 and 2 BVDV Bovine Viral Diarrhea Virus, Model for Hepatitis C Virus PRV Pseudorabies Virus, Model for Herpes Viruses PPV Porcine Parvovirus, Model for Parvovirus B19 EMC Encephalomyocarditis Virus, Model for Hepatitis A Virus WNV West Nile Virus HAV Hepatitis A Virus ND Not Determined N/A Not Applicable
Lipid Enveloped	Yes	Yes	Yes	No	No	Yes	No
Size (nm)	80-120	40-70	120-200	18-24	25-30	40-60	27-32
Genome	SS-RNA	SS-RNA	DS-DNA	SS-DNA	SS-RNA	SS-RNA	SS-RNA
Fractionation	≥ 7.98	7.29	≥ 11.74	8.30	ND	ND	ND
Viral Filtration	≥ 5.60	5.40	≥ 6.20	3.30	4.16	ND	≥ 5.07
Viral Inactivation	≥ 4.28	≥ 4.90	≥ 5.58	N/A	N/A	≥ 7.05	N/A
Total Viral Reduction	≥ 17.86	≥ 17.59	≥ 23.52	11.60	4.16	≥ 7.05	≥ 5.07

The safety of Rh_o(D) Immune Globulin (Human) has been further shown in an empirical study of viral marker rates in female blood donors in the United States.²¹ This study revealed that Rh-negative donors, of whom an estimated 55-60% had received Rh_o(D) Immune Globulin (Human) for pregnancy-related indications, had prevalence and incidence viral marker rates similar to those of Rh-positive female donors who had not received Rh_o(D) Immune Globulin (Human).

The final product contains 5 ± 1% IgG, 2.9 mg/mL sodium chloride, 0.01% Polysorbate 80 (non-animal derived) and 15 mg/mL glycine. Small amounts of IgA, typically less than 15 μg per dose, are present.¹⁰ The pH range is 6.20 - 6.55 and IgG purity is ≥ 98%. The product contains no added human serum albumin (HSA), no thimerosal or other preservatives and utilizes a latex-free delivery system.

RhoGAM Ultra-Filtered PLUS and MICRhoGAM Ultra-Filtered PLUS are manufactured and distributed by Ortho-Clinical Diagnostics, Inc., Raritan, NJ 08869.

CLINICAL PHARMACOLOGY

Mechanism of Action

RhoGAM and MICRhoGAM act by suppressing the immune response of Rh-negative individuals to Rh-positive red blood cells. The mechanism of action is unknown. RhoGAM, MICRhoGAM and other Rh_o(D) Immune Globulin (Human) products are not effective in altering the course or consequences of Rh immunization once it has occurred.

Pharmacokinetic Properties

Pharmacokinetic studies after intramuscular injection were performed on sixteen Rh-negative subjects receiving a single dose of (368 μg or 1840 IU) RhoGAM.¹⁰ Plasma anti-D levels were monitored for thirteen weeks using a validated Automated Quantitative Hemagglutination method with sensitivity of approximately 1 ng/mL. The following mean pharmacokinetic parameters were obtained from data collected over the first ten weeks of a thirteen-week study:

Parameter	Mean	SD	Units
Maximum plasma concentration obtained (Cmax)	54.0	13.0	ng/mL
Time to attain Cmax (Tmax)	4		days
Elimination half-life (T1/2)	30.9	13.8	days
Volume of distribution (Vd)	7.3	1.5	liters
Clearance (CL)	150.4	53.3	mL/day

Obstetrical Use

The Rh-negative obstetrical patient may be exposed to red blood cells from her Rh-positive fetus during the normal course of pregnancy or after obstetrical procedures or abdominal trauma.

Use after Rh-Incompatible Transfusion

An Rh-negative individual transfused with one unit of Rh-positive red blood cells has about an 80% likelihood of producing anti-D.⁴ However, Rh immunization can occur after exposure to < 1 mL of Rh-positive red blood cells. Protection from Rh immunization is accomplished by administering ≥ 20 μg of RhoGAM or MICRhoGAM per mL of Rh-positive red blood cells within 72 hours of transfusion of incompatible red blood cells.^13,22

CLINICAL STUDIES

Rh_o(D) Immune Globulin (Human) administered at 28 weeks, as well as within 72 hours of delivery, has been shown to reduce the Rh immunization rate to about 0.1-0.2%.^23,24 Clinical studies demonstrated that administration of MICRhoGAM within three hours following pregnancy termination was 100% effective in preventing Rh immunization.²⁵

Multiple studies have been performed that prove the safety and efficacy of RhoGAM in both the obstetrical and post transfusion settings.

Freda, Gorman and colleagues^{26, 27} studied the efficacy of RhoGAM in the postpartum setting in a randomized, controlled study completed in 1967. The control group received no immunoglobulin therapy after delivery, while the test group received 300 μg of RhoGAM intramuscularly within 72 hours of delivery of an Rh-positive infant. Six months after delivery, the incidence of Rh immunization in the control group was 6.4% (32/499) versus 0.13% (1/781) in the RhoGAM group (p < 0.001).

Pollack et al. performed two randomized, placebo-controlled studies in the post transfusion setting that were designed to establish the dose response relationship of RhoGAM. In the first study,¹⁵ 178 (176 males, 2 females) Rh-negative volunteers received varying volumes of Rh- positive red cells; 92 subjects then received RhoGAM. A single dose of RhoGAM (1.1 mL @ 267 μg/mL) was shown to suppress anti-D formation after injection of up to 15.1 mL of Rh-positive red cells. In a companion study,⁴ Pollack administered 500 mL of Rh-positive whole blood to 44 Rh-negative male volunteers. Twenty-two (22) subjects received 20 μg RhoGAM per mL of Rh-positive red cells and 22 received no RhoGAM. None of the RhoGAM-treated subjects developed anti-D; 18/22 control arm subjects developed anti-D (p < 0.0001).

Human clinical studies¹⁰ were subsequently performed to prove the efficacy of MICRhoGAM and the low protein (5%) formulations. In the MICRhoGAM study, 81 Rh-negative male volunteers received an initial injection of 2.5 mL Rh-positive red cells, followed by a booster injection (0.1 mL) of red cells at 26 weeks; 40 subjects received an injection of MICRhoGAM after the initial red cell injection. None of the subjects who received MICRhoGAM developed anti-D, both before and after the booster red cell injection. A similar study was performed in 1985 using the low protein formulation of RhoGAM. None of the 30 Rh-negative male volunteers who received RhoGAM after injection of 15 mL of Rh-positive red cells developed anti-D.