Thallium-201 is used to detect myocardial perfusion. It is used in conjunction with exercise and pharmacological stress to diagnose and localize myocardial ischemia and infarction.

Thallium-201 Indications:

• Myocardial perfusion imaging:

  • It is used as an imaging modality with planar scintigraphy or single-photon emission computed tomography (SPECT) for the diagnosis and localization of coronary artery disease (to detect reversible myocardial ischemia and non-reversible myocardial infarction) when used in conjunction with exercise or pharmacologic stress.

• Parathyroid hyperactivity imaging:

  • It is used to localize parathyroid hyperactivity before and after surgery in patients who have hypercalcemia and hyperparathyroidism.

Thallium-201 Dose in Adults

Note: Use the lowest dose necessary. Individualize the dosage.

Thallium-201 Dose in the treatment of Myocardial perfusion: IV:

• Planar scintigraphy:
  • 37 to 74 MBq (1 to 2 mCi)
• Single-photon emission computed tomography (SPECT):
  • 74 to 111 MBq (2 to 3 mCi)

Thallium-201 Dose in the treatment of Parathyroid hyperactivity localization:

• Planar or SPECT:
  • 75 to 130 MBq (2 to 3.5 mCi)

Use in Children:

Not indicated.

Pregnancy Risk Factor C

• Radiopharmaceutical products can cause harm to fetuses, even though animal reproduction studies are not available.
• You may use it during pregnancy only if you feel the benefits outweigh any potential risks.
• Before the patient is allowed to undergo the procedure, they must confirm their pregnancy status.

Use Thallium-201 during breastfeeding

• Breast milk contains thallus chloride Tl201.
• According to the manufacturer, patients should express breastmilk immediately after it is administered and then discard it within two weeks.
• If the administered dose is greater than 1mSv (0.1rem), close contact should be avoided.

Dose in Kidney disease:

There are no dosage adjustments provided in the manufacturer’s labeling.

Dose in Liver disease:

There are no dosage adjustments provided in the manufacturer’s labeling.

Side effects of Thallium-201

• Cardiovascular:

  • Cardiac Arrhythmia
  • Cerebrovascular Accident
  • Flushing
  • Hypotension
  • Myocardial Infarction

• Central Nervous System:

  • Chills

• Dermatologic:

  • Diaphoresis
  • Pruritus
  • Skin Rash

• Gastrointestinal:

  • Mild Diarrhea
  • Nausea
  • Vomiting

• Hypersensitivity:

  • Anaphylactoid Reaction

• Neuromuscular & Skeletal:

  • Tremor

• Ophthalmic:

  • Blurred Vision
  • Conjunctivitis

• Respiratory:

  • Bronchoconstriction
  • Dyspnea

• Miscellaneous:

  • Fever

Contraindications to Thallium-201:

The manufacturer's labeling does not contain any contraindications

Warnings and precautions

• Cardiovascular events

  • There have been reports of patients suffering from cardiac arrhythmias and bronchoconstriction.
  • Patients also reported chest pain, abnormal ECG readings, fluctuation in blood pressure readings, myocardial injury, and cerebrovascular events.
  • It is recommended to keep an eye on the patient. Cardiac imaging should include measures to revive the patient.

• Hypersensitivity reactions

  • Allergies, including anaphylactoid reactions, may manifest as flushing, hypotension and pruritus.

• Reactions from the local community:

  • Redness, pain, burning and other symptoms that can occur at the injection site include redness, pain, swelling, and inflammation.
  • You can avoid local tissue accumulation and radiation by placing the needle/cannula correctly before injecting intravenously.

• Latex

  • Some products may contain latex in the vial stopper.

Monitoring parameters:

Observe the patient for allergic reactions and anaphylaxis.

How to administer Thallium-201?

• It is an intravenous radiopharmaceutical agent that requires appropriate precautions for handling and disposal.
• It is intended for intravenous use only. Because it may extravasate, intravenous patency must be confirmed prior to the injection.

Myocardial perfusion imaging:

• Images may be taken 10 - 20 minutes after the administration of the injection (for resting myocardial studies).
• Injection in the upright and fasting state may improve the myocardial-to-background ratio images.
• The upright posture reduces hepatic and gastric thallium Tl-201 concentration.
• For exercise stress testing, the injection may be administered at the start of the maximum stress which should be sustained for at least 30 seconds after the injection.
• Images may be taken 10 minutes after the drug administration for maximum target-to-background ratios.

Parathyroid hyperactivity localization:

• It is administered before, with, or after a minimal dose of appropriate thyroid imaging agents such as sodium pertechnetate Tc 99m or sodium iodide I-123 to enable thyroid subtraction imaging.

Mechanism of action of Thallium-201:

• It is radioactive diagnostic material, which decays to mercury Hg201 through electron capture.
• This can be detected using imaging. Regional myocardial perfusion correlates with the distribution of radioactive material.

Distribution:

• It is primarily distributed in the myocardium, liver, kidneys, thyroid, and stomach.

Half-life elimination:

• Bi-exponential:
  • The initial radioactive half-life: about 5 minutes;
  • The remainder in about 40 hours;
  • Biologic half-life: 2.4 days

Time to peak:

• Myocardium uptake: About 10 minutes

Excretion:

• Urine (4% to 8% of injected activity within 24 hours);
• feces

International Brand Names of Thallium-201:

• (201 TI) Tallium-Klorid
• Ari Thallous Chloride
• Cloreto de Talio (201 TI) Solucao
• Cloruro De Talio (201 TI)
• Thallous (201 T) Chloride
• Thallous (TI 201) Chloride

Thallium-201 Brand Names in Pakistan:

Available in specific centers in Pakistan.