External Radiation

The specific gamma ray constant for Cr 51 is 0.19 R/hour-millicurie at 1 cm. The first half-value layer is 0.20 cm lead (Pb). Values for the relative attenuation of the radiation emitted by the radionuclide that result from interposition of two thicknesses of Pb are shown in Table 2. To facilitate control of the radiation exposure from millicurie amounts of this radionuclide, the use of a 0.60 cm thickness of lead will attenuate the radiation emitted by a factor of about 10.

To correct for physical decay of CR 51, the fractions that remain at selected intervals before and after the time of calibration are shown in Table 3.

General

In the use of any radioactive material, care should be taken to insure minimum radiation exposure to the patient and occupational workers consistent with proper patient management.

Nuclear medicine procedures involving withdrawal and reinjection of blood have the potential for transmission of blood borne pathogens. Procedures should be implemented to avoid administration errors and viral contamination of personnel during blood product labeling. A system of checks similar to the ones used for administering blood transfusions should be routine.

In order to obviate or minimize the possibility of contamination and of increased fragility of the labeled red blood cells, sterile techniques should be employed throughout the collection, labeling, rinsing, suspending, and injection of red blood cells. In addition, the number of washes and transfers should be kept to a minimum and only sterile, non-pyrogenic isotonic diluent should be employed throughout the labeling procedure.

Radiopharmaceuticals should be used only by physicians who are qualified by training and experience in the safe use and handling of radionuclides and whose experience and training have been approved by the appropriate government agency authorized to license the use of radionuclides.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term studies in animals have not been performed to evaluate carcinogenic or mutagenic potential, or whether this agent may impair fertility in males or females.

Nursing Mothers

Caution should be exercised when Sodium Chromate Cr 51 Injection is administered to a nursing woman since chromium 51 is excreted in human milk during lactation. Therefore, formula feedings should be substituted for breast feedings.

Pediatric Use

Safety of the chromium 51-labeled suspension of red blood cells in children has not been established.

Red Blood Cell Labeling Procedure

Labeling may be performed without washing or centrifugation steps directly in the silicone-coated reaction vial of Bracco A-C-D Solution Modified.*

*Anticoagulant Acid Citrate Dextrose Solution Modified containing the same ingredients as Anticoagulant Citrate Dextrose Solution USP but in different ratio (see package insert for complete details). Bracco A-C-D Solution Modified is supplied as 10 mL of sterile, nonpyrogenic solution in convenient silicone-coated 75 mL capacity reaction vials.

A 30 to 50 mL sample of whole blood is withdrawn from the patient and added aseptically to a vial of Bracco A-C-D Solution Modified. 1.85 to 5.55 megabecquerels (50 to 150 microcuries) of Chromitope Sodium (Sodium Chromate Cr 51 Injection USP) is then injected into the reaction vial using a shielded syringe. The amount of radioactivity added to the vial will depend on the intended use of the labeled red blood cells. The suspension is incubated for 30 to 60 minutes at room temperature with frequent gentle agitation. After incubation, 100 mg Ascorbic Acid Injection USP is injected into the vial. The ascorbic acid reduces any remaining unbound dianionic chromium 51 to the anionic state which does not penetrate red blood cells; thus in vivo labeling of red blood cells is prevented.

The extent of chromium 51 labeling is influenced by hematocrit values; hematocrits below 35 percent will result in a higher degree of labeling, whereas hematocrits exceeding 45 percent will produce the opposite result. Although the rate of labeling is initially more rapid at 37° C, samples incubated at 37° C and room temperature will show the same degree of chromium 51 labeling after a 30-minute period.

Labeling may also be accomplished by centrifugation and washing techniques which are described in the literature.

The admixture of Sodium Chromate Cr 51 Injection with Bracco A-C-D Solution Modified (Anticoagulant Citrate Dextrose Solution Modified) for use as a stock solution is not recommended. For best results, the whole blood sample should be combined with Bracco A-C-D Solution Modified prior to labeling.

Radiation Dosimetry

The estimated absorbed radiation doses to an average patient (70 kg) following an intravenous injection of 7.40 megabecquerels (200 microcuries) of Cr 51 are shown in Table 4.

Storage

Store the product as supplied at 20-25 °C (68-77 °F) [See USP]; avoid excess heat.

Disposal

Any unused portion of the labeled preparation must be stored and disposed of in accordance with the conditions of NRC radioactive material license pursuant to Agreement State Regulation.

The U.S. Nuclear Regulatory Commission has approved this prepared radiopharmaceutical for distribution to persons licensed to use byproduct material identified in §35.100 of 10 CFR Part 35, to persons who hold an equivalent license issued by an Agreement State, and, outside the United States, to persons authorized by the appropriate authority.