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Thallous Chloride Tl-201 Injection (thallous chloride) is supplied in an isotonic solution as a sterile, non-pyrogenic diagnostic radiopharmaceutical for intravenous administration. Each milliliter contains 37 megabecquerels (1 millicurie) Thallous Chloride Tl-201 at calibration time, made isotonic with 9 milligrams sodium chloride and preserved with 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 Tl-201 is cyclotron produced. At the time of calibration it contains no more than 1.0% Thallium Tl-200, no more than 1.0% Thallium Tl-202, no more than 0.25% Lead Pb-203, and no less than 98% Thallium Tl-201 as a percentage of total activity. No carrier has been added.
It is recommended that Thallous Chloride Tl-201 be administered close to calibration time to minimize the effect of higher levels of radionuclidic contaminants present at pre- and post-calibration dates. The concentration of each radionuclidic contaminant changes with time. Figure 1 shows maximum concentration of each radionuclidic contaminant as a function of time.
Figure 1. Radionuclidic Contaminants
 |
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 thallium Tl-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 1. Principal Radiation Emission Data
| Radiation | MeanPercent/ 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 Tl-201 is 4.7 R/mCi-hr2 at 1 cm. The first half-value thickness of lead (Pb) is 0.0006 cm. A range of values for the radiation emitted by this radionuclide with the corresponding exposure rate at 1 cm that results from interposition of various thicknesses of lead 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.
Table 2. Radiation Attenuation by Lead Shielding
| cm of Lead(Pb) | Coefficient of Attenuation |
| 0.0006 | 0.5 |
| 0.015 | 10-1 |
| 0.098 | 10-2 |
| 0.21 | 10-3 |
| 0.33 | 10-4 |
To correct for physical decay of the radionuclide, the fractions that remain at selected intervals after calibration time are shown in Table 3.
Table 3. Thallium Tl-201 Decay Chart; Half-Life 73.1 Hours
| Hours | Fraction Remaining | Hours | Fraction Remaining |
| 0* | 1.00 | 66 | 0.53 |
| 6 | 0.94 | 72 | 0.51 |
| 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 | 0.71 | 108 | 0.36 |
| 42 | 0.67 | 120 | 0.32 |
| 48 | 0.63 | 132 | 0.29 |
| 54 | 0.60 | 144 | 0.26 |
| 60 | 0.57 | ||
| *Calibration Time | |||
REFERENCES
1. Kocher, David C., "Radioactive Decay Data Tables," DOE/TIC- 11026, 181 (1981).
2. Includes 10 keV x-rays.
Thallous Chloride Tl 201 Injection is a diagnostic radiopharmaceutical indicated for
Thallous Chloride Tl 201 Injection emits radiation and must be handled with appropriate safety measures and in accordance with the “as low as reasonably achievable” (ALARA) principle of radioactivity dosing.
Use the lowest dose of Thallous Chloride Tl 201 Injection necessary to obtain the intended diagnostic image. Individualize the dose and consider factors such as body size, and the equipment and technique to be employed.
Planar or SPECT: 75 to 130 MBq (2 to 3.5 mCi) administered intravenously
For resting myocardial studies, begin imaging 10 to 20 minutes after injection of Thallous Chloride Tl 201. Myocardial-to-background ratios are improved when patients are injected upright and in the fasting state; the upright position reduces the hepatic and gastric thallium Tl-201 concentration.
For exercise stress testing administer Thallous Chloride Tl 201 Injection at the start of a period of maximum stress which is sustained for approximately 30 seconds after injection. Begin imaging within ten minutes after administration to obtain maximum target-to-background ratios. Within two hours after the completion of the stress testing the target-to-background ratios may decrease in lesions that are attributable to transient ischemia.
For localization of parathyroid hyperactivity, administer Thallous Chloride Tl 201 Injection before, with or after a minimal dose of a thyroid imaging agent such as sodium pertechnetate Tc 99m or sodium iodide I-123 to enable thyroid subtraction imaging.
The estimated absorbed radiation doses at calibration time to a 70 kg patient from an intravenous injection of Thallous Chloride Tl 201 are shown in Table 1. The estimates were calculated based on human data from Krahwinkel et al.1 and Thomas et al.2 Assumed percentages of 98.3% 201Tl, 0.3% 200Tl, 1.2% 202Tl, and 0.2% 203Pb. The effective dose was calculated using ICRP 103 tissue weighting factors and assumptions on the biodistribution data based on data from Krahwinkel et al. and Thomas et al.
Table 1: Radiation Dose Estimates for Thallous Chloride Tl 201 (includes contaminants)
| Organ | Estimated Radiation Dose | |
| mGy/MBq | rad/mCi | |
| Adrenals | 6.33E-02 | 2.34E-01 |
| Brain | 5.68E-02 | 2.10E-01 |
| Breasts | 3.39E-02 | 1.25E-01 |
| GB Wall | 8.31E-02 | 3.07E-01 |
| LLI Wall | 2.96E-01 | 1.09E+00 |
| Small Intestine | 3.79E-01 | 1.40E+00 |
| Stomach | 1.71E-01 | 6.34E-01 |
| ULI Wall | 2.97E-01 | 1.10E+00 |
| Heart Wall | 2.47E-01 | 9.14E-01 |
| Kidneys | 4.10E-01 | 1.52E+00 |
| Liver | 9.39E-02 | 3.47E-01 |
| Lungs | 4.73E-02 | 1.75E-01 |
| Muscle | 4.59E-02 | 1.70E-01 |
| Ovaries | 1.02E-01 | 3.76E-01 |
| Pancreas | 7.52E-02 | 2.78E-01 |
| Red Marrow | 4.44E-02 | 1.64E-01 |
| Bone Surfaces | 9.37E-02 | 3.47E-01 |
| Skin | 3.16E-02 | 1.17E-01 |
| Spleen | 1.66E-01 | 6.14E-01 |
| Testes | 2.09E-01 | 7.73E-01 |
| Thymus | 4.60E-02 | 1.70E-01 |
| Thyroid | 5.42E-01 | 2.00E+00 |
| Urinary Bladder Wall | 6.25E-02 | 2.31E-01 |
| Uterus | 8.63E-02 | 3.19E-01 |
| Total Body Effective Dose | 5.77E-02 0.145mSv/MBq | 2.14E-01 0.535rem/mCi |
Thallous Chloride Tl 201 Injection is supplied as a sterile, non-pyrogenic solution for intravenous administration.
Table 2: Strengths Available
| Total Radioactivity* per Vial (*At time of calibration) | |
| MBq | mCi |
| 103.6 | 2.8 |
| 207.2 | 5.6 |
| 233.1 | 6.3 |
| 366.3 | 9.9 |
Thallous Chloride Tl 201 Injection is supplied in a sterile, non-pyrogenic solution for intravenous administration (Table 6). Each mL contains 37 MBq (1 mCi) Thallous Chloride Tl 201 at calibration time, 9 mg sodium chloride and 0.9 percent (v/v) benzyl alcohol. The pH is adjusted to between 4.5 to 7.0 with hydrochloric acid and/or sodium hydroxide solution.
Table 6: Thallous Chloride TI 201 Injection
| NDC | Vial | ||
| Volume | Activity | ||
| mL | megabecquerels | millicuries | |
| 69945-120-28 | 2.8 mL | 103.6 | 2.8 |
| 69945-120-56 | 5.6 mL | 207.2 | 5.6 |
| 69945-120-63 | 6.3 mL | 233.1 | 6.3 |
| 69945-120-99 | 9.9 mL | 366.3 | 9.9 |
The contents of the vial are radioactive. Adequate shielding and handling precautions must be maintained.
Store this drug at controlled room temperature, 20° to 25°C (68° to 77°F).
Storage and disposal of Thallous Chloride Tl 201 Injection should be controlled in a manner that is in compliance with the appropriate regulations of the government agency authorized to license the use of this radionuclide.
REFERENCES
1. Krahwinkel W, Herzog H, Feinendegen LE. Pharmacokinetics of thallium-201 in normal individuals after routine myocardial scintigraphy. J Nucl Med, 1988; 29, 1582–1586.
2. Thomas SR, Stabin MG, Castronovo FP. Radiation-absorbed dose from 201Tl-thallous chloride. J Nucl Med, 2005; 46(3), 502-508.
Manufactured by: Curium US LLC, Maryland Heights, MO 63043, Made in USA. Revised: Dec 2019
The most frequently reported reactions were itching, nausea, vomiting, mild diarrhea, tremor, shortness of breath, chills, fever, conjunctivitis, sweating, and blurred vision.
The following adverse reactions have been identified during post-approval use of Thallous Chloride Tl 201. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure: Injection site reactions and extravasation of Tl-201 have been reported: burning, pain, redness, swelling, warmth, and, in one case, tissue damage with chronic ulcer formation
Drugs that increase or decrease myocardial blood flow or potassium uptake might correspondingly alter the biodistribution of Thallous Chloride Tl 201.
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 procedures. 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.
Pharmacologic induction of cardiovascular stress may be associated with serious adverse events such as myocardial infarction, arrhythmia, hypotension, bronchoconstriction, and cerebrovascular events. Caution should be used when pharmacologic stress is selected as an alternative to exercise; it should be used when indicated and in accordance with the pharmacologic stress agent's labeling.
Data are not available concerning the effect on the quality of Thallous Chloride Tl-201 images of marked alterations in blood glucose, insulin or pH (such as is found in diabetes mellitus). Attention is directed to the fact that thallium is a potassium analog, and since the transport of potassium is affected by these factors, the possibility exists that the Thallous Chloride Tl-201 may likewise be affected.
This drug should not be used after six (6) days from the calibration date, or nine (9) days from date of manufacture, whichever comes first.
As in the use of any radioactive material, care should be taken to minimize radiation exposure to the patient consistent with proper management and to insure minimum radiation exposure to occupational workers.
Radiopharmaceuticals should be used only by physicians who are qualified by training and experience in the safe use and handling of radionuclides.
No long-term animal studies have been performed to evaluate carcinogenic potential, mutagenic potential or whether this drug affects fertility in males or females.
Animal reproductive studies have not been conducted with Thallous Chloride Tl-201. It is also not known whether Thallous Chloride Tl-201 can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Thallous Chloride Tl-201 should be given to a pregnant woman only if clearly needed.
It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, as a general rule nursing should not be undertaken when a patient is administered radioactive material.
Safety and effectiveness in pediatric patients below age 18 have not been established.
In the event of the administration of a radiation overdose with Thallous Chloride Tl 201, the absorbed dose to the patient should be reduced where possible by increasing the elimination of the radionuclide from the body by forced diuresis with frequent voiding and stimulation of the gastrointestinal passage.
None.
Thallous Chloride Tl 201 with no carrier added accumulates 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 correlates well with regional perfusion.
In clinical studies, Thallous Chloride Tl 201 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 Thallous Chloride Tl 201 was administered in conjunction with an exercise stress test. Anatomic configurations may interfere with visualization of the right coronary artery.
After intravenous administration, Thallous Chloride Tl 201 clears rapidly from the blood with maximal concentration by normal myocardium occurring at about 10 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 is primarily by the myocardium, thyroid, liver, kidneys and stomach with the remainder distributing fairly uniformly throughout the body. The dosimetry data in Table 1 reflect this distribution pattern and are based on a biological half-life of 2.4 days. Thallous Chloride Tl 201 is excreted slowly and to an equal extent in both feces and urine.
Five minutes after intravenous administration only 5 to 8 percent of injected activity remained in the blood. A biexponential disappearance curve was obtained, with 91.5 percent of the blood radioactivity disappearing with a half-time of about 5 minutes. The remainder had a half-time of about 40 hours.
Approximately 4 to 8 percent of the injected dose was excreted in the urine in the first 24 hours. The whole body disappearance half-time was 9.8 ± 2.5 days. Kidney concentration was found to be about 3 percent of the injected activity and the testicular content was 0.15 percent. Net thyroid activity was determined to be only 0.2 percent of the injected dose, and the activity disappeared in 24 hours. From anterior and posterior whole-body scans, it was determined that about 45 percent of the injected dose was in the large intestines and contiguous structures (liver, kidneys, abdominal musculature).
Advise patients to inform their physician or healthcare provider if they are pregnant or breast-feeding.
