SELENOMETHIONINE SE 75
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SELENOMETHIONINE SE 75 (SELENOMETHIONINE SE 75).
Radiopharmaceutical agent: selenium-75 decays by electron capture to arsenic-75 with emission of gamma photons. Used as a tracer for pancreatic imaging due to incorporation into pancreatic enzymes. Localizes in pancreas via protein synthesis.
| Metabolism | Not metabolized; incorporated into proteins (e.g., glutathione peroxidase) in tissues, primarily pancreas, liver, and kidneys. Excreted via urine and feces with long biological half-life. |
| Excretion | Primarily renal, with 20-30% excreted unchanged in urine; minor fecal elimination (<5%). The remainder is incorporated into endogenous proteins and long-term tissue stores. |
| Half-life | Terminal half-life is approximately 50-60 days, reflecting slow turnover of selenomethionine incorporated into body proteins (e.g., skeletal muscle, erythrocytes). |
| Protein binding | Approximately 30% bound to plasma proteins, predominantly albumin and globulins (e.g., selenoprotein P). |
| Volume of Distribution | Vd is approximately 0.3-0.6 L/kg, indicating distribution primarily into extracellular and intracellular fluid, with extensive tissue retention. |
| Bioavailability | Intravenous only (100% bioavailability). Oral absorption of non-radioactive selenomethionine is ~90%, but this form is not used therapeutically due to radiation safety. |
| Onset of Action | Not applicable (radiopharmaceutical for imaging; no direct clinical effect). Uptake into target tissues (e.g., pancreas) occurs within 1-2 hours post-intravenous injection. |
| Duration of Action | Effective imaging can be performed 2-4 hours post-injection, with residual activity detectable for weeks due to protein incorporation. |
0.185-0.37 MBq (5-10 μCi) intravenously as a single dose for pancreatic imaging.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment guidelines are established; however, because of the low administered activity, dose adjustment is not typically required for renal impairment. Use with caution in severe renal failure. |
| Liver impairment | No specific dose adjustment guidelines are established; use with caution in severe hepatic impairment as the agent is excreted via the biliary system. |
| Pediatric use | Weight-based dosing calculated as adult dose proportionally reduced based on body weight or body surface area, using the formula: Pediatric dose (MBq) = Adult dose (MBq) × (weight [kg]/70) or (BSA/1.73). The minimum dose should be sufficient to obtain diagnostic images. |
| Geriatric use | No specific dose adjustment required; standard adult dose is appropriate, but consider reduced renal and hepatic function with age and monitor accordingly. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SELENOMETHIONINE SE 75 (SELENOMETHIONINE SE 75).
| Breastfeeding | Excreted into human milk. M/P ratio not available. Radioactivity may accumulate in infant thyroid. Discontinue breastfeeding for at least 4 weeks after administration to minimize radiation exposure to infant. |
| Teratogenic Risk | No adequate studies in pregnant women. Animal reproduction studies not conducted. Radioactive iodine isotopes may cause fetal thyroid damage after the first trimester due to fetal thyroid uptake of iodide. Selenomethionine Se 75 is a radiopharmaceutical; fetal exposure to radiation increases risk of teratogenesis and childhood cancer. Risk is highest during organogenesis (first trimester) and lower but still significant in second and third trimesters. |
■ FDA Black Box Warning
None
| Common Effects | No common side effects seen |
| Serious Effects |
["Absolute: Known hypersensitivity to selenium-75 or any component.","Relative: Pregnancy (unless diagnostic necessity), lactation (temporary cessation)."]
| Precautions | ["Radiation exposure risk (carcinogenic, teratogenic) - ALARA principles.","Hypersensitivity reactions (rare).","Ensure adequate hydration to minimize radiation dose to bladder.","Use in pregnancy only if benefit outweighs risk; lactating women should pump and discard milk for 24-48 hours."] |
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| Fetal Monitoring | Monitor fetal radiation exposure; ensure maternal hydration to promote radionuclide excretion. Assess fetal thyroid function if exposure occurs after first trimester. Follow institutional radiation safety protocols. No specific maternal laboratory monitoring required. |
| Fertility Effects | No data on fertility effects. Ionizing radiation may cause gonadal injury at high doses; however, diagnostic doses of Se-75 are unlikely to impair fertility. |