GLOFIL^®-125
Sodium Iothalamate I-125 Injection, USP

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 uled in Table 1.

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.

To correct for physical decay of this radionuclide, the fractions that remain at selected time intervals after the date of calibration are shown in Table 3.

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.

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.

None known.

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 workers.

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.

No long-term animal studies have been performed to evaluate carcinogenic potential, mutagenic potential, or whether this drug affects fertility in males or females.

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.

None reported.

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.

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%.

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.

Table 3 provides the required factors for the determination of activity per mL post calibration date for GLOFIL^®-125 sterile solution.

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.

• 3. 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.
• 4. Skov PE. Glomerular filtration rate in patients with severe and very severe renal insufficiency. Acta Med Scand 1970; 187: 419-428.