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
A. 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.
A. Administration of Dose
1. Inject the dose into a large vein in patient's arm. Measure the residual radioactivity
in the syringe and needle.
2. 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.
3. At 5 and 15 minutes after injecting the dose, withdraw blood samples from the
patient's other arm with a sterile heparinized syringe.
B. Calculation of Blood Volume
1. Take a known aliquot from each blood sample and determine radioconcentration
in net cpm/mL.
2. 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.
3. Calculate the patient's blood volume (in mL) using the following formula:
Net cpm/mL reference solution × DF = blood volume (in mL)
Net cpm/mL patient's blood sample
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 52,430 x 4000 = 4360 mL
48,100
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:
1. Withdraw background blood sample from large vein in patient's arm with a sterile
heparinized syringe.
2. Leaving needle in patient's vein, detach syringe containing blood sample.
3. Attach syringe containing the dose of Megatope to the indwelling needle and
administer (see instructions under Blood Volume Determination, Administration of
Dose).
4. 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
Net cpm/mL Net cpm/mL volume
postinjection minus background
blood sample blood sample (in mL)
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 × DF = plasma volume
Net cpm/mL patient's plasma sample (in mL)
Cardiac Output
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.
Radiation Dosimetry
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.
