Ga67 Gallium Citrate Radiopharmaceutical

Summary / Explanation

Gallium citrate Ga 67 is a diagnostic radiopharmaceutical imaging agent used in nuclear medicine for scintigraphy. This diagnostic imaging technique uses gamma rays emitted by a radioactive tracer to create images of specific organs or areas in the body. Ga 67 is incorporated into the citrate molecule to form gallium citrate Ga 67. This radiopharmaceutical is known for its affinity to certain types of tissues, including primary and metastatic tumors, as well as sites of infection. The exact mechanism by which gallium citrate Ga 67 concentrates in these areas is not fully understood, and it may accumulate in lysosomes within cells. Lysosomes are cellular organelles involved in the breakdown of various substances. Another proposed mechanism involves binding gallium citrate Ga 67 to soluble intracellular proteins. The concentration of the radiopharmaceutical in these specific tissues allows for the detection of abnormalities or pathological conditions during imaging procedures.[1][2][3] Generally, gallium citrate Ga 67 scintigraphy is useful in detecting tumors, inflammation, and infections.

Indications

Gallium citrate Ga 67 injection is approved as a diagnostic tool for Hodgkin's disease, lymphoma, and bronchogenic carcinoma. If there is a positive uptake of gallium Ga 67 without preceding symptoms, further investigation is advisable to assess the potential development of a disease. Gallium citrate Ga 67 injection can also be beneficial as a supplementary method for identifying certain acute inflammatory lesions.[1][4][5]

Dosage

The recommended dosage range for intravenous administration of gallium citrate Ga 67 is 74 to 185 megabecquerels (2-5 millicuries) for an average adult weighing 70 kg. Patients are advised to use daily laxatives and/or enemas during the week following the injection to minimize bowel exposure to radiation until the final images are acquired. The dosage should be measured with an appropriate calibration device immediately before administration. Research indicates that the most optimal images are typically obtained approximately 48 hours (within a range of 6 to 120 hours) after administration. Notably, the safety and efficacy of gallium citrate Ga 67 in children have not been established.

Pharmacokinetics

Onset, duration, and absorption: Although the peak concentration ratios between tumors and background tissues are typically achieved around 48 hours after injection, satisfactory images can be obtained within a range of 6 to 120 hours post-injection. The estimated absorbed radiation doses vary for different organs following the intravenous injection of 185 megabecquerels of gallium citrate Ga 67, with values of over 20 milligrays per injection for the lower large intestine, bone marrow, upper large intestine, spleen, liver, skeleton, and kidneys.

Distribution, half-life, and excretion: Gallium citrate Ga 67 exhibits an affinity for lysosomes, where it binds with soluble intracellular proteins. Besides tumors and infection sites, the renal cortex initially shows the highest tissue concentration of gallium Ga 67. Notably, a day after gallium citrate Ga 67 injection, the peak concentration shifts from the renal cortex to bone and lymph nodes. Following this, 1 week post-injection, the highest concentration transitions from bone and lymph nodes to the liver and spleen.[6]

The half-life of gallium citrate Ga 67, which undergoes decay by electron capture, is 78.3 hours. Excretion is relatively gradual; 7 days after the injection of gallium citrate Ga 67, 26% of the dose is excreted in the urine, 9% in the feces, and 65% remains retained in the body.

Adverse Effects, Contraindications, and Precautions

Occasional occurrences of skin rash, nausea, and allergic reactions have been documented. Conclusive contraindications have not been identified. Exposure to patients and healthcare personnel should be minimized. In certain situations, false-negative results of up to 40% may occur; therefore, a negative study does not conclusively negate the possibility of disease presence. This diagnostic agent is not recommended for patients with lymphocytic lymphoma, as adequate accumulation may not be achieved for definitive imaging.

Pregnancy and lactation: The potential for gallium citrate Ga 67 to cause fetal harm is uncertain. There are no published human or animal studies investigating pregnancy outcomes following exposure to gallium citrate Ga 67 injection, and no reports exist regarding outcomes after unintended exposure during pregnancy. Nevertheless, Ga 67 can accumulate in the placenta.[7][8] Therefore, it is advised to administer gallium citrate Ga 67 to pregnant patients only when deemed necessary.

Ga 67 tends to accumulate in the breast, even in patients who are not lactating.[9] Notably, concentrations have been found in the breast milk of a postpartum woman 10 days after receiving the dose.[10] The specific concentration may vary depending on factors such as milk flow volume and the breastfeeding stage.[11] The manufacturer suggests replacing breast milk with formula. Because Ga 67 has a prolonged half-life, guidelines advise discontinuing breastfeeding for a minimum of 2 to 4 weeks after the injection to minimize exposure to the nursing infant.

Storage and stability: The administration of Gallium citrate Ga 67 injection is restricted to intravenous use exclusively. The intravenous solution should be stored within a controlled room temperature range, specifically between 20 and 25 °C. Notably, the expiration date for the solution is set at 14 days from the calibration date.