GLOFIL®-125 (Sodium Iothalamate I-125 Injection)
is a sterile, nonpyrogenic aqueous injection containing approximately 1 mg
sodium iothalamate per mL, and 0.9 percent benzyl alcohol as a preservative.
The radioactive concentration of the material is 250-300 μCi/mL as
of the calibration date. Sodium bicarbonate and hydrochloric acid are present
for pH adjustment.
Iodine-125 decays by electron capture with a physical half-life
of 60.14 days. Photons that are useful for detection are listed in Table 1.
ICRP Publication 38: Radionuclide Transformations - Energy and Intensity of Emissions. Published for the International Commission on Radiological Protection by Pergamon Press, New York, 1983, p. 446.
Mean Number Per
The specific gamma ray constant for I-125 is 1.43 R/mCi-hr at 1 cm. The first
half value thickness of lead (Pb) for I-125 is 0.017 mm. A range of values for the relative attenuation of the radiation emitted by this radionuclide resulting from interposition of various thicknesses of Pb is shown in Table 2. For example, the use of 0.28 mm of Pb will decrease the external radiation exposure by a factor of 10,000.
The renal clearance of sodium iothalamate in man closely
approximates that of inulin. The compound is cleared by glomerular filtration
without tubular secretion or reabsorption. Following infusion administration
of I-125 iothalamate, the effective half-life is about 0.07 days.
INDICATIONS AND USAGE
GLOFIL®-125 (Sodium Iothalamate I-125 Injection)
is indicated for evaluation of glomerular filtration in the diagnosis or monitoring
of patients with renal disease.
GLOFIL®-125 should not be administered via
a central venous line.
As in the use of any radioactive material, care should be
taken to minimize radiation exposure to the patient, consistent with proper
patient management, and to insure minimum radiation exposure to occupational
Radiopharmaceuticals should be used only by
physicians who are qualified by training and experience in the safe use and
handling of radionuclides.
Rapid or bolus-like injections should be avoided.
Carcinogenesis, Mutagenesis, Impairment of Fertility
No long-term animal studies have been performed to evaluate
carcinogenic potential, mutagenic potential, or whether this drug affects fertility in males or females.
Pregnancy Category C
Animal reproduction studies have not been conducted with
GLOFIL®-125. It is also not known whether GLOFIL®-125
can cause fetal harm when administered to a pregnant woman or can affect reproduction
capacity. GLOFIL®-125 should be given to a pregnant woman
only if clearly needed.
Radioiodine is excreted in human milk during lactation. It
is not known whether GLOFIL®-125 is excreted in human milk.
Therefore, formula feedings should be substituted for breast feedings.
Safety and effectiveness in children have not been established.
DOSAGE AND ADMINISTRATION
The suggested dose range employed in the average patient (70 kg) is as follows: Continuous intravenous infusion: 20 to 100 μCi (0.74-3.7 megabecquerels) (Sigman, et al (1) method). Single intravenous injection: 10 to 30 μCi (0.37-1.11 megabecquerels) (Cohen, et al (2) method). The patient dose should be measured by a suitable radioactivity calibration system immediately prior to administration.
Adequate diuresis (a urine flow exceeding 3 mL/min.) is established, preferably by an oral water load of 1,500 mL two hours prior to the beginning of the clearance study.
It is not necessary to withhold breakfast or admit the patient the night before.
After the establishment of adequate diuresis, a number 14 or 16 French
Foley catheter is aseptically inserted into the bladder.
An intravenous infusion of Lactated Ringer’s (Hartmann’s)
solution is started in each arm, one to maintain a site for injection of the
GLOFIL®-125, the other to serve as a site for serial withdrawal
of blood. A two-way stopcock connects the needle and intravenous tubing of
The dose is equally divided into (1) an intravenous priming dose to
be injected as is and (2) a sustaining dose to be diluted in 30 to 60 mL of
isotonic sodium chloride, depending on how many collection periods are anticipated.
The priming dose is slowly injected into one arm. This is immediately
followed by infusion of the sustaining solution through the same site, usually
at the rate of 0.5 mL/min., by means of an automatic pump. During this
infusion, the Lactated Ringer’s solution in the same arm is discontinued,
and 40 to 45 minutes are allowed for equilibration in order to reach a state
of constant plasma concentration of radioactivity.
After attaining equilibrium, consecutive 15 minute collection periods
are started. From the arm opposite the injection site, 5 mL of blood (allowing duplicate
plasma counting volumes) is drawn six minutes prior to the midpoint of each
collection period, placed in heparinized tubes, mixed, and centrifuged. The
blood samples may be obtained through the two-way stopcock after discarding the
first 30 mL aspirated into the syringe. This 30 mL contains the contents of
the tubing, including infusion fluid, and must be cleared in order to obtain
an undiluted blood sample. If desired, this step may be eliminated and blood
samples obtained by direct venipuncture.
During each collection period, total urine must be accurately collected
and the volume accurately measured. Three such consecutive collection periods
are sufficient for most clinical studies.
III. Clearance Calculations:
Aliquots (1 mL each) of plasma and urine from each collection period
are counted in a standard gamma-ray scintillation well detector.
All counts are corrected for background activity.
Glomerular filtration rate is calculated by the formula C=UV/P, in which: C = glomerular filtration rate in mL/min U= urinary concentration of radioactivity in net counts/min/mL V= urinary flow rate in mL/min P = plasma concentration of radioactivity in net counts/min/mL
Average glomerular filtration rate (GFR) is calculated from the rates
for the individual collection periods. GFR can be expressed in terms of body
weight (mL/min/kg) or body surface area (mL/min/m2).
Unilateral glomerular filtration rates can be determined by the same
technique by utilizing ureteral catheterization.
The method of Cohen, et al (2) requires little preparation, few and small blood samples, no bladder catheterization, and no constant intravenous infusion. It is simple to perform, rapid, and
utilizes equipment which is readily available in most modern laboratories.
Lugol's solution, 3 drops orally, three times a day, is administered
for one or two days prior to the test.
No diet or water restriction is necessary.
Oral water load is begun one hour before starting the test. Start with
20 mL/kg and force any clear liquids (unless contraindicated) until the test
Record actual times for the collection of the blood and urine samples.
Empty the bladder and label the urine Urine control.
Inject 10-30 μCi GLOFIL®-125 intravenously; wait 30 to 60 minutes.
Collect the entire urine and label Urine discard.
Draw 4 to 5 mL of blood into a heparinized syringe. Label
After another 30 to 60 minutes, collect the entire urine and label
Immediately draw another blood specimen. Label
After final 30 to 60 minute wait, collect the urine. Label Urine #2.
Draw the last blood specimen immediately. Label
III. Clearance Calculations:
Radioactivity of one mL aliquots of both urine and plasma are determined using a well-scintillation detector with a single channel pulse-height analyzer. Sufficiently reproducible counts are usually obtained with time settings of 2 minutes for urine samples and 20 minutes for the plasma samples. Calculations of the clearance rates are made by using the formula:(1)
C = UV/P + 1.73/SA where
C = glomerular filtration rate in mL/min/1.73 m2
U = urine radioactivity in counts/min/mL
V = urine flow rate in mL/min
P= mean plasma radioactivity in counts/min/mL
SA= body surface area in m2
The estimated absorbed radiation doses to an average (70 kg)
patient from an intravenous dose of 100 μCi (3.7 megabecquerels) of
GLOFIL®-125 are shown in Table 4. Calculations assume that
there is 1% free iodide in the preparation and that the thyroid uptake of
the iodine is 25%.
Data supplied by Oak Ridge Associated Universities, Radiopharmaceutical Internal Dose Information Center, Oak Ridge, TN, 1988.
Absorbed radiation doses for 100 µCi (3.7 megabecquerels)
2 hour bladder voiding interval
4.8 hour bladder voiding interval
Lower Large Intestine Wall
Upper Large Intestine Wall
Urinary Bladder Wall
Parenteral drug products should be inspected visually for
particulate matter and discoloration prior to administration, whenever solution
and container permit.
No. 1000, GLOFIL®-125 is a clear, colorless,
sterile, and nonpyrogenic solution available as a 4 mL vial. It is supplied
in a concentration of approximately 1 mg/mL sodium iothalamate (range is 0.5–2.0
mg sodium iothalamate per mL), with a radioactivity concentration of 250 to
300 μCi/mL at the time of calibration. Benzyl alcohol 0.9%, is added as
a preservative. Sodium bicarbonate and hydrochloric acid are added for pH
adjustment. The calibration and expiration dates are shown on the label.
Refrigerate the product upon receipt at 2°C to 8°C.
Dose Volume Calculation
Table 3 provides the required factors for the determination
of activity per mL post calibration date for GLOFIL®-125 sterile
To determine the dose volume, locate the decay
factor (fraction remaining) which corresponds to the day that the dose is
to be administered. The following equation is then utilized to determine
the dose volume:
(activity of desired dose) /[(decay factor) x (amount of activity/mL on calibration day)] = dose volume (mL)(information on label)
Sigman EM, Elwood CM, Reagan ME, Morris AM, Catanzaro A. The renal clearance of 131I labeled sodium iothalamate in man. Invest Urol 1965; 2:432.
Cohen ML, Smith FG Jr., Mindell RS, Vernier RL. A simple reliable method of measuring glomerular filtration rate using single low dose sodium iothalamate 131I.Pediatrics 1969; 43:407.
Maher FT, Nolan NG, Elveback LR. Comparisons of simultaneous clearances of 125I-labeled sodium iothalamate (Glofil) and of Inulin. Mayo Clin Proc 1971; 46: 690-691.
Skov PE. Glomerular filtration rate in patients with severe and very severe renal insufficiency. Acta Med Scand 1970; 187: 419-428.
Manufactured by Iso-Tex Diagnostics, Inc. for QOL Medical