THALLOUS CHLORIDE TL 201- thallous chloride, tl-201 injection, solution
TCI Medical, Inc.

For Diagnostic Use

DESCRIPTION

Thallous Chloride Tl 201 is supplied in isotonic solution as a sterile, non-pyrogenic diagnostic radiopharmaceutical for intravenous administration. The aqueous solution at the time of calibration contains 74 MBq/mL (2 mCi/mL) Thallous Chloride Tl 201. The pH is adjusted with hydrochloric acid and/or sodium hydroxide solution. It is made isotonic with 9 mg/mL sodium chloride and is preserved with 9 mg/mL benzyl alcohol.

Thallium Tl 201 is accelerator produced with no carrier added and contains no less than 98% Thallium Tl 201 as a percentage of total activity with contaminants less than 0.3% Thallium Tl 200, 1.2% Thallium Tl 202, and 0.2% Lead Pb 203 expressed as a percentage of Tl 201 Injection activity at calibration.

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

(click image for full-size original)

Graph 1. Radionuclidic Contaminants

Physical Characteristics

Thallium Tl 201, with a physical half-life of 73.1 hours, decays by electron capture to Mercury Hg 201.1 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 to 80.3 keV is much greater than the combination of gamma-4 and gamma-6 mean %/disintegration.

1

Martin, M.J., Nuclear Data Project, ORNL, January 1977.

External Radiation

The specific gamma ray constant for Thallium Tl 201 is 33 micro-coulombs/Kg MBq-hr (4.7R/mCi-hr) at 1 cm. The first half-value layer is 0.0006 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 0.21 cm of lead will decrease the external radiation exposure by a factor of about 1,000.

In making dosage calculations, correct for 73.1 hour radioactive half-life of Tl 201. To correct for physical decay of this radionuclide, the fractions that remain at selected intervals before and after calibration are shown in Table 3.

CLINICAL PHARMACOLOGY

Thallous Chloride Tl 201 with no carrier added has been found to accumulate in viable myocardium in a manner analogous to that of potassium. Experiments in human volunteers using labeled microspheres have shown that the myocardial distribution of Thallous Chloride Tl 201 Injection correlates well with regional perfusion.

In clinical studies, Thallium images have been found to visualize areas of infarction as “cold” or nonlabeled regions which were confirmed by electrocardiographic and enzyme changes. When the “cold” or nonlabeled regions comprise a substantial portion of the left ventricle, the prognosis for survival is unfavorable. Regions of transient myocardial ischemia corresponding to areas perfused by coronary arteries with partial stenoses have been visualized when Thallous Chloride Tl 201 Injection was administered in conjunction with an exercise stress test. Body habitus may interfere with visualization of the inferior wall.

After intravenous administration, Thallous Chloride Tl 201 Injection clears rapidly from the blood with maximal concentration by normal myocardium occurring at about ten minutes. It will, in addition, localize in parathyroid adenomas; it is not specific since it will localize to a lesser extent in sites of parathyroid hyperplasia and other abnormal tissues such as thyroid adenoma, neoplasia (e.g., parathyroid carcinoma) and sarcoid. Biodistribution is generally proportional to organ blood flow at the time of injection. Blood clearance of Thallous Chloride Tl 201 Injection is primarily by the myocardium, kidneys, thyroid, liver and stomach with the remainder distributing fairly uniformly throughout the body. The dosimetry data in Table 4 reflect this distribution pattern and are based on a biological half-life of 11 days and an effective half-life of 2.4 days. Thallous Chloride Tl 201 Injection is excreted slowly and to an equal extent in both feces and urine. This technique has limited sensitivity for detecting parathyroid adenomas smaller than 5 mm in diameter.