Thallous Chloride Tl 201

Thallous Chloride Tl 201

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Side Effects & Adverse Reactions

When studying patients suspected or known to have myocardial infarction or ischemia, care should be taken to assure continuous clinical monitoring and treatment in accordance with safe, accepted procedure. Exercise stress testing should be performed only under the supervision of a qualified physician and in a laboratory equipped with appropriate resuscitation and support apparatus.

The contents of this vial are radioactive. Adequate shielding of the preparation must be maintained at all times.

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Thallous Chloride Tl 201 may be useful in myocardial perfusion imaging for the diagnosis and localization of myocardial infarction. It may also have prognostic value regarding survival, when used in the clinically stable patient following the onset of symptoms of an acute myocardial infarction, to assess the site and size of the perfusion defect.

Thallous Chloride Tl 201 may also be useful in conjunction with exercise stress testing as an adjunct in the diagnosis of ischemic heart disease (atherosclerotic coronary artery disease) .

It is usually not possible to differentiate recent from old myocardial infarction, or to differentiate exactly between recent myocardial infarction and ischemia.

Thallous Chloride Tl 201 is indicated also for the localization of sites of parathyroid hyperactivity in patients with elevated serum calcium and parathyroid hormone levels. It may also be useful in pre-operative screening to localize extrathyroidal and mediastinal sites of parathyroid hyperactivity and for post-surgical reexamination. Thallous Chloride Tl 201 has not been adequately demonstrated to be effective for the localization of normal parathyroid glands.


There is currently no drug history available for this drug.

Other Information

Thallous Chloride Tl 201 Injection is supplied in isotonic solution as a sterile, nonpyrogenic, diagnostic radiopharmaceutical for intravenous administration. Each unit dose contains 1 mL and each milliliter contains 37 MBq (1 mCi) of Thallous Chloride Tl 201 Injection at calibration time. The pH is adjusted to 4.5-7.5 with hydrochloric acid or sodium hydroxide. It is made isotonic with 9 mg sodium chloride/mL and is preserved with 0.009 mL benzyl alcohol/mL.

Thallium Tl 201 is cyclotron produced with no carrier added. The radionuclidic composition at calibration time, expressed as percent of total activity, is not less than 98 percent Thallium Tl 201 with not more than 0.3 percent Thallium Tl 200 , not more than 1.2 percent Thallium Tl 202, not more than 0.2 percent Lead Pb 203, and not more than 0.3 percent all others.

The concentration of each radionuclidic contaminant changes with time. Therefore, it is recommended that Thallous Chloride Tl 201 Injection be administered close to calibration time to minimize the effect of higher levels of radionuclidic contaminants pre and post calibration. Graph 1 shows maximum allowable concentration of each radionuclidic contaminant as a function of time.

Graph 1. Radionuclidic Contaminants
Image from Drug Label Content


Thallium Tl 201 decays by electron capture to Mercury Hg 201 with a physical half-life of 73.1 hours. Photons that are useful for detection and imaging are listed in Table 1. The lower energy x-rays obtained from the Mercury Hg 201 daughter of Tl 201 are recommended for myocardial imaging because the mean %/disintegration at 68.9-80.3 keV is much greater than the combination of gamma-4 and gamma-6 mean %/disintegration.

Table 1. Principal Radiation Emission Data*
Energy (keV)
Kocher David C, "Radionuclidic Decay Data Tables." DOE/TIC-11026, 182 (1981)
Gamma-4  2.7135.3
Mercury x-rays94.468.9-80.3

The specific gamma ray constant for Thallium Tl 201 is 3.21 microcoulombs/hr-kg-MBq (0.46 R/hr-mCi) at 1 cm. The first half-value layer is 0.023 cm of lead. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from the interposition of various thicknesses of lead (Pb) is shown in Table 2. For example, the use of 0.31 cm of lead will decrease the external radiation exposure by a factor of about 1,000.

Table 2. Radiation Attenuation by Lead Shielding*
cm of Lead (Pb)Coefficient of Attenuation
Method of calculation: Data dated 1984 supplied by Oak Ridge Associated Universities. Radiopharmaceutical Internal Dose Information Center.
0.19  10-2
0.31  10-3
0.44  10-4

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

Table 3. Thallium Tl 201 Decay Chart: Half-life 73.1 Hours
Calibration time

At two and four days post calibration, Thallium Tl 201 concentrations amount only to about 63% and 40%, respectively, of their initial value. This condition would require use of proportionately larger volume doses.

Thallous Chloride Tl 201 Manufacturers

  • Ge Healthcare, Medi-physics, Inc.
    Thallous Chloride Tl 201 (Thallous Chloride, Tl-201) Injection, Powder, Lyophilized, For Solution [Ge Healthcare, Medi-physics, Inc.]
  • Lantheus Medical Imaging, Inc.
    Thallous Chloride Tl 201 (Thallous Chloride Tl-201) Injection, Solution [Lantheus Medical Imaging, Inc.]
  • Mallinckrodt Inc.
    Thallous Chloride Tl 201 (Thallous Chloride, Tl 201) Injection, Solution [Mallinckrodt Inc.]

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