thallous chloride tl 201 - Generic Medications

11.1 Drug Characteristics Thallous Chloride Tl 201 Injection is a sterile, radioactive diagnostic drug for intravenous use. Each mL contains 37 MBq (1 mCi) thallous chloride Tl 201 at calibration time and the following inactive ingredients: 9 mg sodium chloride and 0.9% (v/v) benzyl alcohol. The pH is adjusted to between 4.5 to 7.0 with hydrochloric acid and/or sodium hydroxide. Thallium-201 is cyclotron produced. At the time of calibration it contains no more than 1% thallium-200, no more than 1% thallium-202, no more than 0.25% lead-203, and no less than 98% thallium-201 as a percentage of total activity. No carrier has been added. The concentration of each radionuclidic contaminant changes with time. Figure 1 shows maximum concentration of thallium-200 (Tl 200) and thallium-202 (Tl 202) radionuclidic contaminants as a function of time. Figure 1. Radionuclidic Contaminants figure 1 11.2 Nuclear Physical Characteristics Thallium-201, with a physical half-life of 72.9 hours, decays by electron capture to mercury-201. Photons that are useful for detection and imaging are listed in Table 2. The lower energy x-rays obtained from the mercury-201 daughter of thallium-201 are recommended for myocardial imaging, because the mean percent disintegration at 68.9 to 80.3 keV is much greater than the combination of gamma-4 and gamma-6 mean percent disintegration. Table 2. Principal Radiation Emission Data Radiation Mean Percent/ Disintegration Energy (keV) Gamma-4 2.7 135.3 Gamma-6 10.0 167.4 Mercury x-rays 94.4 68.9-80.3 The specific gamma ray constant for thallium-201 is 0.45 R/mCi-hr at 1 cm. The first half-value thickness of lead (Pb) is 0.026 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 3. For example, the use of 0.194 cm of lead will decrease the external radiation exposure by a factor of about 1,000. Table 3. Radiation Attenuation by Lead Shielding cm of Lead (Pb) Coefficient of Attenuation 0.026 0.5 0.052 10 -1 0.089 10 -2 0.194 10 -3 0.310 10 -4 To correct for physical decay of the radionuclide, the fractions that remain at selected intervals after calibration time are shown in Table 4. Table 4. Physical Decay Chart for Thallium-201; Half-Life 72.9 Hours Hours Fraction Remaining Hours Fraction Remaining 0* 1 66 0.53 6 0.95 72 0.50 12 0.89 78 0.48 18 0.84 84 0.45 24 0.80 90 0.43 30 0.75 96 0.40 36 0.74 108 0.36 42 0.67 120 0.32 48 0.63 132 0.29 54 0.60 144 0.25 60 0.57 * Calibration Time