SODIUM IODIDE I 123

Sodium Iodide I 123 (Na 123 I) for diagnostic use is supplied in capsules for oral administration. The capsules are available in strengths of 3.7 and 7.4 megabecquerels (MBq) (100 and 200 μCi) I 123 at time of calibration. Each capsule contains 0.3 µg - 3 µg Sodium Thiosulfate as a stabilizer. The radionuclidic composition at calibration is not less than 97.0 percent I 123, not more than 2.9 percent I 125 and not more than 0.1 percent all others (I 121 or Te 121.) The radionuclidic composition at expiration time is not less than 87.2 percent I 123, not more than 12.4 percent I 125 and not more than 0.4 percent all others. The ratio of the concentration of I 123 and I 125 changes with time. Graph 1 shows the maximum concentration of each as a function of time. Graph 1 Radionuclidic Concentration of I 123 and I 125 Physical Characteristics Sodium Iodide I 123 decays by electron capture with a physical half-life of 13.2 hours. The photon that is useful for detection and imaging studies is listed in Table 1 . Table 1 Principal Radiation Emission Data 1 1 Kocher, David C., Radioactive Decay Data Tables, DOE/TIC-11026, 122, (1981) Radiation Mean %/Disintegration Mean Energy (keV) Gamma-2 83.4 159 External Radiation The specific gamma ray constant for I 123 is 1.6 R/hr-mCi at 1 cm. The first half value thickness of lead (Pb) for I 123 is 0.005 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from the interposition of various thicknesses of Pb is shown in Table 2 . For example, the use of 1.63 cm of lead will decrease the external radiation exposure by a factor of about 1,000. Table 2 Radiation Attenuation by Lead Shielding 2 2 Shleien, Bernard, The Health Physics and Radiological Health Handbook, Table 6.1.2, 169, (1992) Shield Thickness (Pb), cm Coefficient of Attenuation 0.036 0.5 0.120 10 -1 0.240 10 -2 0.358 10 -3 0.477 10 -4 Note that these estimates of attenuation do not take into consideration the presence of contaminants. To correct for physical decay of I 123, the fractions that remain at selected intervals after the time of calibration are shown in Table 3 . Table 3 Sodium Iodide I 123 Decay Chart: Half-Life 13.2 Hours *Time of Calibration Hours Fraction Remaining Hours Fraction Remaining 0* 1.000 18 .389 3 .854 21 .332 6 .730 24 .284 9 .623 27 .242 12 .535 30 .207 15 .455 Graph 1

INDICATION AND USE Administration of Sodium Iodide I 123 is indicated as a diagnostic procedure to be used in evaluating thyroid function and/or morphology.

The recommended oral dose for the average patient (70 kg) is 3.7 to 14.8 MBq (100-400 µCi). The lower part of the dosage range 3.7 MBq (100 µCi) is recommended for uptake studies alone, and the higher part 14.8 MBq (400 µCi) for thyroid imaging. The determination of I 123 concentration in the thyroid gland may be initiated at six hours after administering the dose and should be measured in accordance with standardized procedures. The patient dose should be measured by a suitable radioactive calibration system immediately prior to administration. The capsules can be utilized up to thirty (30) hours after calibration time and date. Thereafter, discard the capsules in accordance with standard safety procedures. The user should wear waterproof gloves at all times when handling the capsules or container. Radiation Dosimetry The estimated absorbed radiation doses to several organs of an average patient (70 kg) from oral administration of the maximum dose of 14.8 MBq (400 µCi) of I 123 are shown in Table 4 for thyroid uptakes of 5, 15, and 25%. For comparison at these three values of thyroid uptake, the estimated radiation doses from doses of 3.7 MBq (100 µCi) I 131, also used as thyroid imaging agent, are also included. Table 4 Radiation Dose Estimates as a Function of Maximum Thyroid Uptake for I 123* Sodium Iodide At Time of Calibration and Expiry Compared to I 131 *Concentration at Time of Calibration: 97% I 123, 2.9% I 125, 0.1% Te 121 Concentration at Time of Expiry: 87.2% I 123, 12.4% I 125, 0.4% Te 121 All Iodine Kinetics treated as in MIRD Dose Estimate Report 5. Bladder voiding interval, 4.8 hours. Tellurium 121 dosimetry taken from ICRP 30. Target Organ Maximum Thyroid Uptake (%) Estimated Radiation Absorbed Doses I 123 mGy/14.8 MBq (rads/400 µCi) I 131 mGy/3.7 MBq (rads/100 µCi) TOC TOE Thyroid 5 25 (2.5) 75 (7.5) 260 (26) 15 77 (7.7) 230 (23) 780 (78) 25 130 (13) 410 (41) 1300 (130) Liver 5 0.089 (0.0089) 0.13 (0.013) 0.16 (0.016) 15 0.10 (0.010) 0.18 (0.018) 0.28 (0.028) 25 0.11 (0.011) 0.24 (0.024) 0.41 (0.041) Ovaries 5 0.18 (0.018) 0.19 (0.019) 0.18 (0.018) 15 0.17 (0.017) 0.18 (0.018) 0.18 (0.018) 25 0.16 (0.016) 0.18 (0.018) 0.17 (0.017) Red Marrow 5 0.12 (0.012) 0.16 (0.016) 0.15 (0.015) 15 0.12 (0.012) 0.18 (0.018) 0.21 (0.021) 25 0.13 (0.013) 0.19 (0.019) 0.27 (0.027) Stomach Wall 5 0.96 (0.096) 0.98 (0.098) 1.7 (0.17) 15 0.89 (0.089) 0.91 (0.091) 1.5 (0.15) 25 0.82 (0.082) 0.85 (0.085) 1.4 (0.14) Small Intestine 5 0.70 (0.070) 0.71 (0.071) 1.2 (0.12) 15 0.65 (0.065) 0.67 (0.067) 1.1 (0.11) 25 0.60 (0.060) 0.62 (0.062) 0.99 (0.099) Testes 5 0.076 (0.0076) 0.089 (0.0089) 0.12 (0.012) 15 0.072 (0.0072) 0.087 (0.0087) 0.12 (0.012) 25 0.068 (0.0068) 0.085 (0.0085) 0.12 (0.012) Bladder 5 1.7 (0.17) 1.7 (0.17) 2.9 (0.29) 15 1.6 (0.16) 1.6 (0.16) 2.7 (0.27) 25 1.4 (0.14) 1.5 (0.15) 2.4 (0.24) Skeleton 5 0.11 (0.011) 0.16 (0.016) 0.12 (0.012) 15 0.12 (0.012) 0.18 (0.018) 0.18 (0.018) 25 0.14 (0.014) 0.21 (0.021) 0.24 (0.024) Total Body 5 0.11 (0.011) 0.16 (0.016) 0.24 (0.024) 15 0.14 (0.014) 0.25 (0.025) 0.47 (0.047) 25 0.17 (0.017) 0.35 (0.035) 0.70 (0.070)

To date there are no known contraindications to the use of Sodium Iodide I 123 capsules.

Although rare, reactions associated with the administration of Sodium Iodide isotopes for diagnostic use include, in decreasing order of frequency, nausea, vomiting, chest pain, tachycardia, itching skin, rash and hives.