Indium In 111 Oxyquinoline

Indium In 111 oxyquinoline is indicated for radiolabeling autologous leukocytes.

Indium In 111 oxyquinoline labeled leukocytes may be used as an adjunct in the detection of inflammatory processes to which leukocytes migrate, such as those associated with abscesses or other infection, following reinjection and detection by appropriate imaging procedures. The degree of accuracy may vary with labeling techniques and with the size, location and nature of the inflammatory process.

Indium In 111 oxyquinoline labeled leukocyte imaging is not the preferred technique for the initial evaluation of patients with a high clinical probability of an abscess in a known location. Ultrasound or computed tomography may provide a better anatomical delineation of the infectious process and information may be obtained more quickly than with labeled leukocytes. If localization by these techniques is successful, labeled leukocytes should not be used as a confirmatory procedure. If localization or diagnosis by these methods fails or is ambiguous, indium In 111 oxyquinoline labeled leukocyte imaging may be appropriate.

The recommended adult (70 kg) dose of indium In 111 oxyquinoline labeled autologous leukocytes is 7.4 to 18.5 MBq, 200-500 µCi. Indium In 111 oxyquinoline solution is intended for the radiolabeling of autologous leukocytes. The indium In 111 oxyquinoline labeled autologous leukocytes are administered intravenously.

Imaging is recommended at approximately 24 hours post injection. Typically, anterior and posterior views of the chest, abdomen and pelvis should be obtained with other views as required.

Aseptic procedures and a shielded syringe should be employed in the withdrawal of indium In 111 oxyquinoline from the vial. Similar procedures should be employed during the labeling procedure and the administration of the labeled leukocytes to the patient. The user should wear waterproof gloves during the entire procedure. The patient's dose should be measured by a suitable radioactivity calibration system immediately before administration. At this time, the leukocyte preparation should be checked for gross clumping and red blood cell contamination.

Sensitivity reactions (urticaria) have been reported. The presence of fever may mask pyrogenic reactions from indium In 111 oxyquinoline labeled leukocytes. The possibility of delayed adverse reactions has not been studied.

Indium In 111 oxyquinoline (oxine) is a diagnostic radiopharmaceutical intended for radiolabeling autologous leukocytes. It is supplied as a sterile, non-pyrogenic, isotonic aqueous solution with a pH range of 6.5 to 7.5. Each mL of the solution contains 37 MBq, 1 mCi of indium In 111 [no carrier added, >1.85 GBq/µg indium (>50 mCi/µg indium)] at calibration time, 50 µg oxyquinoline, 100 µg polysorbate 80, and 6 mg of HEPES (N-2-hydroxyethyl-piperazine-N’-2-ethane sulfonic acid) buffer in 0.75% sodium chloride solution. The drug is intended for single use only and contains no bacteriostatic agent. The radionuclidic impurity limit for indium 114m is not greater than 37 kBq, 1 µCi of indium 114m per 37 MBq, 1 mCi of indium In 111 at the time of calibration. The radionuclidic composition at expiration time is not less than 99.75% of indium In 111 and not more than 0.25% of indium In 114m/114.

Chemical name: Indium In 111 Oxyquinoline.

The precise structure of the indium In 111 oxyquinoline complex is unknown at this time. The empirical formula is (C₉H₆NO)₃ In 111.

Indium forms a saturated (1:3) complex with oxyquinoline. The complex is neutral and lipid-soluble, which enables it to penetrate the cell membrane. Within the cell, indium becomes firmly attached to cytoplasmic components; the liberated oxyquinoline is released by the cell. It is thought likely that the mechanism of labeling cells with indium In 111 oxyquinoline involves an exchange reaction between the oxyquinoline carrier and subcellular components which chelate indium more strongly than oxyquinoline. The low stability constant of the oxyquinoline complex, estimated at approximately 10, supports this theory.

Following the recommended leukocyte cell labeling procedure, approximately 77% of the added indium In 111 oxyquinoline is incorporated in the resulting cell pellet (which represents approximately 3-4 x 10⁸ WBC).

Cell clumping can occur and was found in about one fifth of the leukocyte preparations examined. The presence of red blood cells or plasma will lead to reduced leukocyte labeling efficiency. Transferrin in plasma competes for indium In 111 oxyquinoline.

After injection of labeled leukocytes into normal volunteers, about 30% of the dose is taken up by spleen and 30% by liver, reaching a plateau at 2-48 hours after injection. No significant clearance of radioactivity is observed at 72 hours in these two organs. Pulmonary uptake is 4-7.5% at 10 minutes but is lost rapidly; pulmonary radioactivity is usually visible in scans only up to about 4 hours after injection.

The human biodistribution studies in three normal subjects injected with indium In 111 oxyquinoline labeled leukocytes indicate a biexponential disappearance of indium In 111 from the blood when monitored for up to 72 hours. Between 9.5 to 24.4% of the injected dose remains in whole blood and clears with a biological half-time of 2.8 to 5.5 hours. The remainder (13-18%) clears from blood with a biological half-time of 64 to 116 hours.

Elimination from the body of injected indium In 111 oxyquinoline is probably mainly through decay to stable cadmium since only a negligible amount (less than 1%) of the dose is excreted in feces and urine in 24 hours.

Clearance from whole blood and biological distribution can vary considerably with the individual recipient, the condition of the injected cells and labeling techniques used.

Release of radioactivity from the labeled cells is about 3% at 1 hour and 24% at 24 hours.

Clearance from liver and spleen, for the purpose of calculating the radiation dose, is assumed to be equal to the physical half-life of indium In 111 (67.2 hours).