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Note on this source. The FDA label used for this page covers a combination product listed as Thallous Chloride, Tl 201. The information below therefore describes that product, not Tolnaftate 1% on its own. Check the label of the specific product you have.
Quick facts
- How it is given
- intravenous
- Type
- human prescription drug
We do not publish dosing. How much of this medicine to take, how often, and for how long depends on your age, weight, kidney and liver function, other conditions and other medicines. That is a decision for the person who prescribes or dispenses it. Follow the directions on your own pack and ask your pharmacist if anything is unclear.
What it is used to treat
Thallous Chloride Tl 201 Injection is indicated for use with planar scintigraphy or single-photon emission computed tomography (SPECT) for the following applications: Myocardial perfusion imaging in adults for the diagnosis of coronary artery disease by localization of: Non-reversible defects (myocardial infarction) Reversible defects (myocardial ischemia) when used in conjunction with exercise or pharmacologic stress Localization of sites of parathyroid hyperactivity pre- and post-operatively in adults with elevated serum calcium and parathyroid hormone levels Thallous Chloride Tl 201 Injection is a radioactive diagnostic drug indicated for use with planar scintigraphy or single-photon emission computed tomography (SPECT) for: Myocardial perfusion imaging in adults for the diagnosis of coronary artery disease by localization of: Non-reversible defects (myocardial infarction) Reversible defects (myocardial ischemia) when used in conjunction with exercise or pharmacologic stress Localization of sites of parathyroid hyperactivity pre- and post-operatively in adults with elevated serum calcium and parathyroid hormone levels ( 1 )
About this medicine
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. […]
How it works
12.1 Mechanism of Action Thallous chloride Tl 201 with no carrier added accumulates in viable myocardium in a manner analogous to that of potassium. Experiments in healthy subjects using labeled microspheres have shown that the myocardial distribution of thallous chloride Tl 201 correlates with regional perfusion. In clinical studies, Thallous Chloride Tl 201 images have been found to visualize areas of infarction as “cold” or nonlabeled regions that were 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 Injection was administered in conjunction with an exercise stress test. Anatomic configurations may interfere with visualization of the right coronary artery territory.
Warnings and cautions
Hypersensitivity Reactions: Anaphylactic reactions characterized by cardiovascular, respiratory, and cutaneous symptoms may occur. Have resuscitation equipment and trained staff readily available. ( 5.1 ) Risk Associated with Stress Testing: Induction of cardiovascular stress may be associated with serious adverse reactions. Perform stress testing in a setting where cardiac resuscitation equipment and trained staff are readily available. ( 5.2 ) Radiation Risk: Ensure safe handling to minimize radiation exposure to patients and health care providers. ( 2.1 , 5.3 ) 5.1 Hypersensitivity Reactions Thallous Chloride Tl 201 Injection may cause anaphylactic reactions characterized by cardiovascular, respiratory, and cutaneous symptoms [see Adverse Reactions ( 6 )] . Have resuscitation equipment and trained staff readily available. 5.2 Risks Associated with Stress Testing Induction of cardiovascular stress might be associated with serious adverse reactions such as myocardial infarction, arrhythmia, hypotension or hypertension, ECG abnormalities, chest pain, bronchoconstriction, and cerebrovascular events [see Adverse Reactions ( 6 )] . Perform stress testing in the setting where cardiac resuscitation equipment and trained staff are readily available. Perform pharmacologic stress in accordance with the pharmacologic stress agent’s prescribing information. 5.3 Radiation Risk Thallous Chloride Tl 201 Injection contributes to a patient's overall long-term cumulative radiation exposure. Long-term cumulative radiation exposure is associated with an increased risk of cancer. Ensure safe handling to minimize radiation exposure to patients and health care providers. Advise patients to hydrate before and after administration and to void frequently after administration [see Dosage and Administration ( 2.1 , 2.3 )]. 5.4 Injection Site Reactions and Tissue Damage Injection site reactions and extravasation have been reported after administration of Thallous Chloride Tl 201 Injection [see Adverse Reactions ( 6 )] . Administer Thallous Chloride Tl 201 Injection strictly into the vein to avoid local tissue accumulation and irradiation. Confirm intravenous patency before injection.
Reported side effects
The following clinically significant adverse reactions are described elsewhere in the labeling: Hypersensitivity Reactions [see Warnings and Precautions ( 5.1 )] Risk Associated with Stress Testing [see Warnings and Precautions ( 5.2 )] Injection Site Reactions and Tissue Damage [see Warnings and Precautions ( 5.4 )] The following adverse reactions associated with the use of Thallous Chloride Tl 201 Injection were identified in clinical studies or postmarketing reports. Because some of these reactions were 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: Cardiovascular, respiratory, and cerebrovascular disorders: myocardial infarction, arrhythmia, hypotension, bronchoconstriction, and cerebrovascular events in patients who have undergone stress testing Gastrointestinal disorders: nausea, vomiting, and diarrhea General disorders and administration site conditions: injection site reactions (burning, pain, redness, swelling, warmth, and tissue damage with chronic ulcer formation), chills, fever, and sweating Immune system disorders: hypersensitivity (anaphylaxis, hypotension, shortness of breath, pruritus, flushing, and diffuse rash) The following adverse reactions have been reported. In patients who have undergone stress testing: myocardial infarction, arrhythmia, hypotension, bronchoconstriction, and cerebrovascular events. Adverse reactions in other patients: nausea, vomiting, diarrhea, injection site reactions, chills, fever, sweating, hypersensitivity (anaphylaxis, hypotension, shortness of breath, pruritus, flushing, diffuse rash). ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Curium US LLC at 1-866-789-2211 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.
Use in specific groups
Lactation: Temporarily discontinue breastfeeding. A lactating woman should pump and discard breast milk for at least 96 hours after Thallous Chloride Tl 201 Injection administration. ( 8.2 ) 8.1 Pregnancy Risk Summary There are no data on Thallous Chloride Tl 201 Injection use in pregnant women to evaluate for a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes. Studies using human placentas demonstrate that thallous chloride Tl 201 crosses the placenta. No animal reproductive studies have been conducted. All radiopharmaceuticals, including Thallous Chloride Tl 201 Injection have the potential to cause fetal harm depending on the fetal stage of development and the magnitude of the radiation dose. If considering administration of Thallous Chloride Tl 201 Injection to a pregnant woman, inform the patient about the potential for adverse pregnancy outcomes based on the radiation dose from Thallous Chloride Tl 201 Injection and gestational timing of exposure. The background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defects, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 3% and 10% to 20%, respectively. 8.2 Lactation Risk Summary Thallous chloride Tl 201 has been detected in the milk of lactating women. There are no data on the effects of thallous chloride Tl 201 on milk production or the effects of thallous chloride Tl 201 on the breastfed infant. Exposure of the breastfed infant to thallous chloride Tl 201 can be minimized by advising a lactating woman to temporarily discontinue breastfeeding and pump and discard milk for a minimum of 96 hours after administration of Thallous Chloride Tl 201 Injection. Minimize close contact with infants if the administered dose would result in an effective dose greater than 1 mSv to the infant. […]
If too much is taken
In the event of the administration of an overdose of Thallous Chloride Tl 201 Injection, the absorbed dose to the patient should be reduced where possible by increasing the excretion of the radionuclide by forced diuresis with frequent voiding and stimulation of peristalsis.
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This page is built from the openFDA record of the U.S. Food and Drug Administration's approved labelling for this product, effective 22 December 2025. Label text has been shortened and reformatted for readability; safety wording has not been altered in meaning. FDA labelling describes products approved in the United States — brand names, strengths, formulations and approved uses may differ in your country. Always read the leaflet that comes with your own pack. PocketsInfo is not affiliated with, and is not endorsed by, the FDA. Retrieved 2026-07-30.