THALLOUS CHLORIDE TL 201 INJECTION

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.

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.

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

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 Injection with no carrier added has been found to accumulate in viable myocardium in a manner analogous to that of potassium. Experiments employing labeled microspheres in human volunteers 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 are confirmed by electrocardiographic and enzyme changes. Regions of transient myocardial ischemia corresponding to areas perfused by coronary arteries with partial stenoses have been visualized when thallium was administered in conjunction with an exercise stress test.

Intravenous administration of Thallous Chloride Tl 201 Injection is characterized by rapid biexponential clearance from the blood with about 91.5% of blood radioactivity disappearing with a half-life of approximately 5 minutes and the remainder with a half-life of about 40 hours. Maximal concentration by normal myocardium occurs at about ten minutes with sustained myocardial retention and adequate concentration in heart muscle to permit gated imaging. In addition, localization occurs in parathyroid adenomas and 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.

Do not use after the expiration time and date (5 days maximum after calibration time) stated on the label.

Do not use if contents are turbid.

The patient dose should be measured by a suitable radioactivity calibration system immediately prior to administration.

Thallous Chloride Tl 201 Injection, as well as other radioactive drugs, must be handled with care and appropriate safety measures should be used to minimize radiation exposure to clinical personnel. Also, care should be taken to minimize radiation exposure to patients in a manner consistent with proper patient management.

This radiopharmaceutical is licensed by the Illinois Emergency Management Agency for distribution to persons licensed pursuant to 32 Ill. Admin. Code Section 330.260(a) and Section 335, Subpart D, 335.3010 and Subpart E, 335.4010 or under equivalent licenses of an Agreement State or a Licensing State.

Radiopharmaceuticals should be used only by physicians who are qualified by training and experience in the safe use and handling of radionuclides and whose experience and training have been approved by the appropriate government agency authorized to license the use of radionuclides.

No long-term animal studies have been performed to evaluate carcinogenic potential, mutagenic potential, or whether Thallous Chloride Tl 201 Injection affects fertility in males or females. Ideally, examinations using radiopharmaceuticals, especially those elective in nature, of a woman of childbearing capability should be performed during the first ten days following the onset of menses.

Animal reproduction studies have not been conducted with Thallous Chloride Tl 201 Injection. It is also not known whether Thallous Chloride Tl 201 Injection can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Thallous Chloride Tl 201 Injection should be given to a pregnant woman only if clearly needed.

It has been found that this drug is excreted in human milk during lactation. Therefore, formula feedings should be substituted for breast feedings.

Safety and effectiveness in pediatric patients below the age of 18 have not been established.

Clinical studies of Thallous Chloride TI 201 did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy.

This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.

The estimated absorbed doses at calibration time to an average patient (70 kg) from an intravenous injection of a maximum dose of 74 MBq, 2 mCi of Thallous Chloride Tl 201 Injection are shown in Table 4.

1. Waterproof gloves should be worn during the handling and injection period.
2. Adequate shielding during the life of the radioactive drug should be maintained by using the lead shield and cover and by using a syringe shield for withdrawing and injecting Thallous Chloride Tl 201 Injection.