Thallous Chloride Tl 201 (Intravenous)

As a radiopharmaceutical, Thallous Chloride Tl 201 allows the doctor to see the amount of blood flowing to the heart muscle.


Thallous Chloride Tl 201 is an injection administered by a doctor to help detect certain conditions using myocardial perfusion imaging. It is a diagnostic radiopharmaceutical. Simply put, the injection is part of a procedure that enables the doctor to see how much blood is flowing through the heart in either a resting or exercise (stressed) state. These observations can lead to a diagnosis of heart disease.

Used in planar or single-photon emission computed tomography (SPECT), the medication helps in diagnosis of coronary artery disease. Specifically, it is used to identify myocardial infarction (which is not treatable but contributes to the overall prognosis) and myocardial ischemia (which can be treated).

This medication is also used to locate parathyroid hyperactivity sites. This injection is not effective for locating normally functional parathyroid glands. Patients that have higher serum calcium and parathyroid hormone levels are candidates for the use of Thallous Chloride Tl 201 to identify active areas. Sometimes, this method is used in postsurgical reexamination.

Certain side effects may occur, but many may be avoided if the patient discloses their full medical history to their doctor, including allergies and conditions related to the body's cardiovascular system. The use of Thallous Chloride Tl 201 may be very useful in diagnosing a condition in the patient that may subsequently be treated with the appropriate medications and lifestyle changes.

Conditions treated

Type of Medicine

  • Radiopharmaceutical

Side Effects

There have been reports of anaphylactoid reactions following the injection of this medication. This reaction may include symptoms related to the cardiovascular, respiratory, or cutaneous systems. Some of the symptoms related to these side effects warrant treatment, as they may point to a larger problem. The patient should contact their doctor if they are concerned.

There have also been reports of pruritus, hypotension, flushing, and diffuse rash - which has been shown to respond to antihistamines.

Other side effects associated with the use of Thallous Chloride Tl 201 are:

Some symptoms that arise with the use of a new medication are simply a result of the patient's body getting used to treatment. Therefore, some side effects may lessen as times goes on and the patient's body adjusts. If the patient experiences these symptoms and they do not go away or worsen, they should contact their doctor.

Other side effects that are not listed here may occur. If the patient suspects they are experiencing side effects as a result of this medication and the effects continue or worsen, they should contact their doctor.

To reduce the incidence of side effects, the patient is recommended to tell their doctor about their full health and lifestyle regimen. This includes allergies, medications (prescription and over-the-counter), herbal supplements, vitamins, and the use of alcohol, tobacco, or other drugs.


Dosage of Thallous Chloride Tl 201 is measured by a radioactive calibration system, and should be done immediately before the medication is administered to the patient to ensure accuracy. The medication should be withdrawn using a shielded sterile syringe.

For planar myocardial imaging, the recommended adult dose for intravenous injection is 37 to 74 MBq (1-2 mCi). For SPECT myocardial imaging, the recommended adult dosage is 74 to 111 MBq (2-3 mCi).

For use in the localization of parathyroid hyperactivity, Thallous Chloride Tl 201 is administered to the patient before, during, or after the administration of a thyroid imaging agent (e.g. sodium pertechnetate Tc 99m or sodium iodide I-123), which aids in thyroid subtraction imaging.

Waterproof gloves should be worn by the healthcare professional at all times during the handling of the medication. Products should be looked over for particular matter or discoloration. If the solution appears turbid, it should not be used.

If testing during a resting state, imaging may be done 10-20 minutes after the injection. The patient should receive the injection sitting upright, which improves Myocardial-to-background ratios. This also reduces the hepatic and gastric concentration of Thallium Tl 201.

If testing during exercise stress testing, the medication should be administered when the patient is under maximum stress, to be sustained for about 30 seconds after the injection. Within ten minutes of the injection, imaging should be done for maximum target-to-background ratios. It has been reported that target-to-background ratios decrease significantly within two hours after stress testing, making it harder to detect lesions that may be attributed to transient ischemia.

The patient may be asked by their doctor not to eat or drink anything several hours before the shot is administered.


Using Thallous Chloride Tl 201 with drugs that increase or decrease myocardial blood flow or potassium uptake might affect the biodistribution of the medication. The patient should talk with their doctor about the procedure and strategies for successful treatment.


The patient should tell their doctor about any allergies they may have. Specifically, if the patient has a latex allergy, they should alert their doctor. The vial stopper is made of dry natural rubber (a latex product) and may cause a reaction in someone with a sensitivity. The patient should also disclose allergies to foods, dyes, preservatives, and animals to their doctor so that all precautions may be taken prior to administering the medication.

An allergic reaction called anaphylaxis may occur as a result of this medication. This reaction may be life-threatening and if the patient experiences any symptoms indicative of this condition they should immediately contact their doctor or visit a hospital. Signs to watch out for are: clammy skin; confusion; feeling dizzy or lightheaded; rash, itching, or sweating; facial, tongue, or throat swelling or redness of the face, neck, arms, or upper chest; trouble breathing; and chest pain.

If the patient experiences redness or pain at the injection site or a feeling of warmth or coldness near the injection site, they should contact their doctor.

The administration of Thallous Chloride Tl 201 may coincide with the use of a medication to make the patient's heart beat faster to stress the heart muscle and aid in the detection of a condition. The patient should talk to their doctor if they have questions or are concerned.

Stress testing may incur some risk. The patient should only undergo such treatment by a doctor trained in the proper procedures in a facility that has the equipment for resuscitation in case of emergency. Patients that are known to have or are suspected of having myocardial infarction or ischemia should be closely watched by their doctor throughout the procedure. The patient should tell their doctor if they have a history of heart attack, heart rhythm problems, high blood pressure, low blood pressure, or stroke.

When pharmacologic stress is used in lieu of exercise to increase blood flow, the patient should be advised that there is a risk that cardiovascular stress may accompany events like myocardial infarction, arrhythmia, hypotension, bronchoconstriction, or cerebrovascular events.

The patient should talk to their doctor if they are pregnant or plan on becoming pregnant. There are potential radiation exposure risks to a fetus associated with Thallous Chloride Tl 201. Not enough long-term research has been done to determine the effect of this medication on childbirth. Nursing mothers should also take caution about using this drug. It common for medications to pass into breastmilk and that information is not known about this medication. The patient is advised to avoid breastfeeding while under treatment with this medication, as the material is radioactive.

There is not enough research to determine if it is safe or effective for young (pediatric) patients to use this medication. Use in older (geriatric) patients will likely not pose any problems, though geriatric patients are more likely to have conditions related with age like problems of the liver, kidney, or heart. The dosage of this medication might need to be adjusted to account for these age-related conditions.


Thallous Chloride Tl 201 is a sterile, non-pyrogenic solution. It should be stored in a controlled environment at 20 to 25 degrees Celsius (68 to 77 degrees Fahrenheit).

This medication emits radiation and must be handled with all the necessary safety measures.

This drug should be stored in a facility equipped with all the relevant safety equipment and only be handled by health care professionals or qualified physicians experienced with using and handling radionuclides.


Thallous Chloride Tl 201 can be a very useful tool for a patient's doctor to use in order to detect a condition in the heart or parathyroid hyperactivity. The procedure with this medication involves an injection given by a doctor either in a resting state or a state of exercise or cardiovascular stress. Observations can be attained rather quickly after the injection as long as all proper protocols have been followed by the patient and the doctor.

There are possible side effects associated with this medication. If the patient suspects that they are having serious adverse effects to the administration of Thallous Chloride Tl 201, they should contact their doctor immediately, as some side effects can be serious. Conditions related to the heart and cardiovascular health are an important consideration prior to receiving the injection and all relevant history should be disclosed to the patient's doctor to avoid adverse effects and the possibility of making the situation worse.

All the necessary precautions should be taken by the patient, their doctor, and the facility where the medication is being administered, as Thallous Chloride Tl 201 is a radiopharmaceutical and may cause harm if not properly stored, handled, and administered.

When used properly, this medication can help doctors identify conditions before they have become too serious or irreversible. Using Thallous Chloride Tl 201 provides the potential for an extended life if certain threatening conditions are detected early on and treated with the proper measures.

Last Reviewed:
December 24, 2017
Last Updated:
April 05, 2018
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