Kit for the Preparation of Technetium Tc 99m Red Blood Cells

INDICATIONS AND USAGE Technetium Tc 99m red blood cells are used for blood pool imaging, including cardiac first pass and gated equilibrium imaging and for detection of sites of gastrointestinal bleeding.

DOSAGE AND ADMINISTRATION The Instructions for Preparation must be carefully followed for preparing technetium Tc 99m red blood cells using Ultratag™ RBC. The suggested dose range of technetium Tc 99m red blood cells in the average patient (70 kg) is 370 MBq (10 mCi) to 740 MBq (20 mCi). The patient dose should be measured by a suitable radioactivity calibration system immediately prior to administration. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. Aseptic procedures and a shielded syringe should be employed in preparing and withdrawing doses for administration to patients. The user should wear waterproof gloves during the administration procedure.

WARNINGS None known.

CONTRAINDICATIONS None known.

ADVERSE REACTIONS None known.

CLINICAL PHARMACOLOGY In vitro Tc 99m red blood cell labeling is accomplished by adding 1.0 to 3.0 milliliters of autologous whole blood, anticoagulated with heparin or Anticoagulant Citrate Dextrose Solution (ACD), to the reaction vial. A portion of the stannous ion in the reaction vial diffuses across the red blood cell membrane and accumulates intracellularly. The in vitro Tc 99m red blood cell labeling efficiency can decrease in the presence of excess ACD. Excess ACD apparently impairs the diffusion of stannous ion across the red blood cell membrane. Therefore, the ACD concentration used for blood collection should not exceed 0.15 mL ACD per mL of blood. Sodium hypochlorite is then added to the reaction vial to oxidize the extracellular stannous ion. Since the hypochlorite does not cross the red blood cell membrane, the oxidation of stannous ion is selective for the extracellular tin. A citric acid, sodium citrate and dextrose solution is then added to the reaction vial to sequester any residual extracellular stannous ion, rendering it more readily available for oxidation by sodium hypochlorite. Radioactive labeling of the red blood cells is completed by addition of sodium pertechnetate Tc 99m to the oxidized reaction vial. The pertechnetate Tc 99m diffuses across the red blood cell membrane and is reduced by the intracellular stannous ion. The reduced technetium Tc 99m cannot diffuse out of the red blood cell. The red blood cell labeling is essentially complete within 20 minutes of sodium pertechnetate Tc 99m addition to the reaction vial. Red blood cell labeling efficiency of ≥95% is typically obtained using this in vitro labeling procedure. In vitro Tc 99m red blood cell labeling efficiency can decrease when excessive amounts of Tc 99 are allowed to accumulate in the sodium pertechnetate Tc 99m generator eluate; in this situation, efficiency decreases even further if excess (i.e. >0.15 mL per mL of blood) ACD buffer is used. Therefore, long Tc 99 in-growth times are to be avoided; the use of fresh (≤24 hour in-growth time) sodium pertechnetate Tc 99m generator eluate is recommended. After the labeling procedure is completed, the technetium Tc 99m red blood cells are then reinjected intravenously into the patient for gamma scintigraphic imaging. Following intravenous injection, the technetium Tc 99m red blood cells distribute within the blood pool with an estimated volume of distribution of approximately 5.6% of bodyweight. The technetium Tc 99m is well retained in the blood pool with an estimated biological half-life of approximately 29 hours. Of the total technetium Tc 99m retained in the whole blood pool 24 hours after administration, 95% remains bound to the red blood cells. Approximately 25% of the injected dose is excreted in the urine in the first 24 hours.