| *Calibration
Time
CLINICAL PHARMACOLOGY
Following intravenous injection, radioiodinated serum albumin is
uniformly distributed throughout the intravascular pool within 10
minutes; extravascular distribution takes place more slowly. Labeled
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
climinated almost entirely in the urine, only about 2 percent of the
total dose ultimately appearing in the feces. The biologic half-life of
labeled albumin is dependent upon a number of factors, and published
studies have varied considerably in their reporting of this figure. It
has ranged, in the literature, from below 10 days to 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 labeled
albumin. With Jeanatope I-125 the biologic half-life in normal
individuals has been reported to be approximately 14 days.
INDICATIONS AND USAGE
Jeanatope I-125 is indicated for use in the determination of total
blood and plasma volume.
CONTRADICTIONS
At present there are no known contraindications to the use of the
preparation.
WARNINGS
Radiopharmaceuticals should not be administered to patients who are
pregnant or to nursing mothers unless the expected benefit to be gained
outweighs the potential hazards.Since I-125 is excreted in human milk
during lactation, formula-feedings should be substituted for
breast-feedings.Ideally, examinations using radiopharmaceuticals,
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.A few instances of hyperpyrexia and
aseptic (chemical) meningeal irritation have been reported with the use
of this reported with the product in cisternography. This material is
not approved for use in cisternography.
PRECAUTIONS
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.
ADVERSE REACTIONS
Although the immunological properties of serum albumin 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 initial dose.
DOSAGE AND ADMINISTRATION
Radioiodinated serum albumin is administered intravenously.
When a procedure such as blood volume determination is to be repeated,
the total dosage administered in any one week should not exceed 7.4
megabecquerels (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 Iodinated Serum Albumin I-125 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 radioactive
level, it is important to make certain that the radioactivity in the
dose at the time of administration is sufficient for the intended use.
Visual Inspection. Parental drug products should be inspected
visually for particulate matter and discoloration prior to
administration, whenever solution and container permit.
Jeanatope (Iodinated I-125 Albumin injection) may be colorless to
very pale yellow. Solutions with excessive coloration should not be
used.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-125 Albumin.
Total Blood and Plasma Volumes
Dosage may range from .185 to 1.85 megabecquerels (5 to 50
microcuries).
Blood Volume Determination
A. Preparation of Reference Solution
Remote an aliquot 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.
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
U.S. Nuclear Regulatory Commission or Agreement State regulations
pertaining to the disposal of radioactive waste.
3. At 5 to 15 minutes after injecting the dose, withdraw blood samples
from the patient's other arm with a sterile heparinized
syringe.
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 to 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 following
formula:
(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 = 1.0
mL
Volume of reference solution aliquot = 1.0 mL
Net counts at zero time =
2500
Net counts obtained from reference solution aliquot = 2725
Using the formula above gives (2725/2500) x 4000 = 4360 mL.
Serial Blood Volume Determinations
Jeanatope (Iodinated I-125 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-125 Albumin is injected.
Background Blood Sample
1. Prior to injecting Jeanatope I-125, 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. Withdraw Jeanatope I-125 from the vial 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 samplers, 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-125 Albumin. The formula for calculating
each blood volume determination after the first one thus becomes:
[Net cpm/mL reference solution / (Net cpm/mL postinjection blood sample
- Net cpm/mL background blood sample)] x 400 = blood volume (in mL)
Plasma Volume DeterminationThe 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 400 = plasma volume (in mL)
Radiation DosimetryThe estimated absorbed radiation doses to an
average patient (70 kg) from an intravenous injection of 1.85
megabecquerels (50 microcuries) of Iodinated I-125 Albumin USP are shown
in
TABLE
4
Estimated Absorbed Radiation Doses |
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