Following intravenous injection, radioiodinated albumin human is
uniformly distributed throughout the intravascular pool within 10
minutes; extravascular distribution takes place more slowly.
Iodinated I 131 albumin also can be detected in the lymph and in
certain body tissues within 10 minutes after injection, but maximum
distribution of radioactivity throughout the extravascular space
does not occur until two to four days after administration. The time
at which extravascular activity is maximal has been designated as
the "equilibrium time." When this point has been reached, the
radioactivity remaining in the intravascular and extravascular
spaces decreases slowly and exponentially in parallel fashion.The
administered radioactivity is eliminated almost entirely in the
urine, only about 2 percent of the total dose ultimately appearing
in the feces. The biologic half-life of iodinated I 131 albumin is
dependent upon a number of factors, and publish studies have varied
considerably in their reporting of this figure. It has ranged, in
the literature, from below 10 days to over 20 days. One important
factor affecting the biologic half-life is the initial rate of
excretion, and this depends in part on the quality of the iodinated
I 131 albumin. With Megatope, the biologic half-life in normal
individuals has been reported to be approximately 14 days.
INDICATIONS AND USAGE
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 delineation,
localization of the placenta, and localization of cerebral
A few instances of hyperpyrexia and aseptic (chemical) meningeal
irritation have been reported with the use of iodinated I 131
albumin in cisternography. Iodinated I 131 Albumin injection is
not approved for use in cisternography.
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.Radiophaemaceuticls 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.
Carcinogens, Mutagenesis, Impairment of Fertility
No long-term animal studies have been performed to evaluate
carcinogenic potential or whether iodinated I 131 albumin affects
fertility in males or females.
Pregnancy Category C
Animal reproduction studies have not been conducted with
Iodinated I 131 Albumin Injection. It is also not known whether this
agent can cause fetal harm when administered to a pregnant woman or
can affect reproduction capacity. Iodinated I 131 Albumin injection
should be administered to a pregnant woman only if clearly
needed.Ideally, examinations using radiopahrmaceuticals, especially
those elective in nature, of a woman of childbearing capability
should be performed during the first few (approximately 10) days
following the onset of menses.
Since iodine 131 is excreted in human milk during lactation ,
formula feedings should be substituted for breast feedings.
Safety and effectiveness in children have not been established.
Although the immunological properties of albumin human are
believed to be virtually unaltered by the iodination process, there
is a theoretical possibility that allergic reactions may occur in
patients receiving additional doses a number of weeks after an
DOSAGE AND ADMINISTRATION
Megatope (Iodinated 131 Albumin Injection) is administered
intravenously. Parental drug products should be inspected
visually for particulate matter and abnormal coloration prior to
administration whenever solution and container permit.Megatope
(Iodinated 131 Albumin Injection) may be colorless to very pale
yellow. Solutions with excessive coloration 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
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
B. 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 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 arm with a sterile
C. 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 at zero
time. The x ordinate of the graph is the sample withdrawal time and
the logarithmic y ordinate is radioconcentration in net cpm/mL.
3. Calculate patient's blood volume (in mL) using the
(Net cpm/mL reference solution / Net cpm/mL patient's blood
sample) x DF = blood volume (in mL)
Sample Blood Volume Calculations
Volume of blood sample aliquot =
Volume of reference solution aliquot = 1.0 mL
Net counts at zero time =
Net counts obtained from reference solution aliquot = 52,430
Using the formula above gives (52,430 / 48,100) 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
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 syringecontaining
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
[Net cpm/mL reference solution / (Net cpm/mL postinjection blood
sample - net cpm/mL background blood sample)] x DF = blood volume
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) x DF = plasma volume (in mL)
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 dose.
Heart and Great Vessel Delineation
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
Localization of Cerebral Neoplasma
The suggested dosage is 5 microcuries per kg of body weight.
Although doses as large as 500 microcuries of Iodinated I 131
Albumin 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