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Kit for the Preparation of Sodium Iodide I 131 Capsules and Solution USP
Therapeutic – Oral


HICON™ is a kit which provides a solution of Sodium Iodide I-131 with a radioconcentration of 37 gigabecquerels/mL (1,000 millicuries/mL). Each mL of the concentrated solution contains 37 GBq of no-carrier-added Sodium Iodide I-131, < 2 mg of Disodium Edetate Dihydrate USP as a stabilizer, < 4.4 mg of Sodium Thiosulfate Pentahydrate USP as a reducing agent, and < 40 mg of Dibasic Sodium Phosphate Anhydrous USP. The pH of the solution is between 7.5 and 9.0.

The concentrated solution provided with HICON™ is intended for use in the preparation of capsules and solution of varying strengths for oral administration for therapy.

Sodium Iodide I 131 Solution USP is designated chemically as Na 131I (MW 153.99, CAS 7790-26-3).

Hard gelatin capsules provided for the preparation of the Sodium Iodide I-131 final dosage form contain approximately 300 mg of Dibasic Sodium Phosphate Anhydrous USP as the absorbing buffer.

Physical Characteristics

Iodine I-131 decays by beta emission and associated gamma emission with a physical half-life of 8.04 days.1 Photons that are useful for detection and imaging are listed in Table 1.

Table 1 : Principal Radiation Emission Data

Radiation Mean % per Disintegration Mean Energy (keV)
Beta-4 (average) 89.3 191.6
Gamma-14 81.2 364.5

1Kocher, David C., “Radioactive Decay Data Tables”, DOE/TIC-11026, (1981) p. 133.

External Radiation

The specific gamma-ray constant for iodine I-131 is 15.8 μC•kg-1•MBq-1•hr-1 (2.27 R/mCi-hr) at 1 cm. The first half-value thickness of lead (Pb) for iodine I-131 is 0.24 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from interposition of various thicknesses of Pb is shown in Table 2. For example, the use of 2.55 cm of Pb will decrease the external radiation exposure by a factor of about 1,000.

Table 2 : Radiation Attenuation by Lead Shielding

Shield Thickness (Pb) cm Coefficient of Attenuation
0.24 0.5
0.89 10-1
1.6 10-2
2.55 10-3
3.73 10-4

To correct for physical decay of iodine I-131, the fractions that remain at selected intervals after the time of calibration are shown in Table 3.

Table 3 : Physical Decay Chart: Iodine I-131, Half-Life 8.04 Days

Days Fraction Remaining Days Fraction Remaining Days Fraction Remaining
0* 1.000 11 .388 22 .151
1 .918 12 .356 23 .138
2 .842 13 .327 24 .127
3 .773 14 .300 25 .116
4 .709 15 .275 26 .107
5 .651 16 .253 27 .098
6 .597 17 .232 28 .090
7 .548 18 .213 29 .083
8 .503 19 .195 30 .076
9 .461 20 .179    
10 .423 21 .164    
*Calibration time

Last reviewed on RxList: 10/6/2011
This monograph has been modified to include the generic and brand name in many instances.


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