Megatope (Iodinated I 131 Albumin Injection) is indicated for use in determinations of total blood and plasma volumes, cardiac output, cardiac and pulmonary blood volumes and circulation times, and in protein turnover studies, heart and great vessel dilineation, localization of the placenta, and localization of celebral neospasms.
DOSAGE AND ADMINISTRATION
Megatope (Iodinated I 131 Albumin Injection) is administered intravenously. Parenteral drug products should be inspected visually for particulate matter and abnormal coloration prior to administration whenever solution and container permit. Megatope (Iodinated I 131 Albumin Injection) may be colorless to very pale yellow. Solutions with excessive colorations should not be used.
When a procedure such as blood volume or a circulation time determination is to be repeated, the total dosage administered in any one week should not exceed 200 microcuries.
To minimize the uptake of radioactive Iodine by the thyroid, prior administration of Lugol's Solution (Strong Iodine Solution USP) may be used. Ten drops of Lugol's Solution three times daily, beginning at least 24 hours before administration of Megatope and continuing for one or two weeks thereafter, is a suitable dose.
Complete assay data for each vial are provided on the container.
Note: The expiration date given on the container pertains to the biologic properties of the material and not to the radioactivity level. It is important to make certain that the radioactivity in the dose at the time of administration is sufficient for the intended use.
The patient dose should be measured by a suitable radioactivity calibration system immediately prior to administration.
Note: A shielded syringe should be used for withdrawing and injecting the iodinated I 131 albumin
Total Blood And Plasma Volumes
Dosage may range from 5 to 50 microcuries.
Blood Volume Determination
Preparation Of Reference Solution
Remove an aliquot of the contents of the vial to be used in the procedure identical in volume to the dose to be administered to the patient. Prepare a reference solution using normal saline as a diluent. The recommended dilution is 1:4000 [Dilution Factor (DF) = 4000]. Determine the radioactivity concentration (net cpm/ml) of the reference solution. Care must be taken to assure that the reference solution and the blood samples (Step B3) are assayed using the same geometric configuration.
Administration of Dose
- Inject the dose into a large vein in patient's arm. Measure the residual radioactivity in the syringe and needle.
- Destroy the syringe after injecting. Do not attempt to resterilize.CAUTION: The syringe should be disposed of in accordance with the US Nuclear Regulatory Commission or Agreement State regulations pertaining to the disposal of radioactive waste.
- At 5 and 15 minutes after injecting the dose, withdraw blood samples from the patient's other arm with a sterile heparinized syringe.
Calculation of Blood Volume
|Net cpm/mL reference solution|
Net cpm/mL patient's blood sample
|× DF = blood volume (in mL)|
- Take a known aliquot from each blood sample and determine radioconcentration in net cpm/mL.
- Plot the 5- and 15-minute sample counts (net cpm/mL) on semilog graph paper using the average count value of each sample and determine the radioconcentration at injection time (zero time) by drawing a straight line through the 15- and 5- minute points to zero time. The x ordinate iof the graph is the sample withdrawal time and the logarithmic y ordinate is radioconcentration in net cpm/mL.
- Calculate the patient's blood volume (in mL) using the following formula:
Sample Blood Volume Calculations
Volume of blood sample aliquot = 1.0 mL
Volume of reference solution aliquot = 1.0 mL
Net counts at zero time = 48,100
Net counts obtained from reference solution aliquot = 52,430
Using the formula above gives
|x 4000||= 4360 mL|
Serial Blood Volume Determinations
Iodinated I 131 Albumin Injection is administered in sufficiently low dosage to permit repetitions as often as required by clinical circumstances. It must be remembered that it is always necessary to correct for background radioactivity remaining in the blood from former determinations. Therefore, for each determination after the first one, a background blood sample must be taken just before the iodinated I 131 albumin is injected.
Background Blood Sample
- Withdraw background blood sample from large vein in patient's arm with a sterile heparinized syringe.
- Leaving needle in patient's vein, detach syringe containing blood sample.
- Attach syringe containing the dose of Megatope to the indwelling needle and administer (see instructions under Blood Volume Determination, Administration of Dose).
- Determine radioconcentration in net cpm/mL of aliquots taken from background and postinjection blood samples, and from the reference solution.
The radioconcentration (net cpm/mL) per aliquot of the background blood sample must be subtracted from the radioconcentration per aliquot of the blood sample obtained after the injection of Iodinated I 131 albumin. The formula for calculating each blood volume determination after the first one thus becomes:
|Net cpm/mL reference solution||× DF =||blood volume (in mL)|
|Net cpm/mL postinjection blood sample||minus||Net cpm/mL background blood sample|
Plasma Volume Determination
The procedure is essentially the same as that for blood volume determination, except that the blood sample drawn from the patient is centrifuged, the red blood cells are removed, and net cpm/mL of the plasma is determined. The formula for calculation of plasma volume, therefore is:
|Net cpm/mL reference solution|
Net cpm/mL patient's plasma sample
|× DF =||plasma volume|
Dosage generally ranges from 3 to 50 microcuries.
Cardiac and Pulmonary Blood Volumes; Circulation Times
Dosages used have generally been 75 to 130 microcuries.
Protein Turnover Studies
Dosages used have ranged from 10 to 150 microcuries. After injection, a period of seven days should be allowed before determinations are made to permit the elimination of any degraded protein in the dose.
Heart and Great Vessel Delineation
The suggested dosage is 5 microcuries per kg of body weight, although doses up to 750 microcuries have been used, depending on the instrumentation available and the scanning technique employed.
Localization of the Placenta
For localization of the placenta in the differential diagnosis of placenta praevia, a 3 to 5 microcurie dose is recommended; this dose has proved adequate for excellent localization, and the fetal total body radiation is a fraction of that received during x-ray placentography. While fetal thyroid irradiation is higher with Iodinated I 131 Albumin Injection than with x-ray placentography, the administration of Lugol's Solution is reported to eliminate this hazard.
Localization of Celebral Neospasms
The suggested dosage is 5 microcuries per kg of body weight. Although doses as large as 500 microcuries of Iodinated I 131 Albumin Injection have been used, the dose should be kept as small as possible. Dosage is administered six hours before the initial examination, and scans are repeated at periodic intervals.
The estimated absorbed radiation doses to an average patient (70 kg) from an intravenous injection of 50 microcuries of Iodinated I 131 Albumin Injection USP are shown in Table 4.
|Estimated Absorbed Radiation Doses|
|Method of Calculation: Hine GJ, Johnston RE: Absorbed Doses from Radionuclides, J. Nucl Med 11:468-469, 1970.|
For doses of 75, 150, 500 and 750 microcuries, the estimated absorbed doses are 1.5, 3, 10 and 15 times the number of rads given, respectively.
Megatope (Iodinated I 131 Albumin Injection USP) is available in multiple dose vials containing the following amounts of activity on the date of calibration: 500 microcuries and 1.0 millicurie. Complete assay data for each vial are provided on the container.
The maximum concentration of Iodinated I 131 Albumin Injection does not exceed one millicurie per milliliter at a time of calibration.
Store between 2° and 8° C.
This radiopharmaceutical is licensed by the Texas Department of Health, Bureau of Radiation Control for distribution to persons licensed pursuant to 41.26(b) and Appendix 41-C, Group I and Group II, "Texas Regulations for Control of Radiation," or under equivalent licenses of the U.S. Nuclear Regulatory Commission, an Agreement State, or a Licensing State.
Manufactured by: Iso-Tex Diagnostics, Inc. P.O. Box 909. Friendswood, Texas 77546. USA. (713) 482-1231. Revised: May 2018