METASTRON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for METASTRON (METASTRON).
Strontium-89 chloride is a bone-seeking radiopharmaceutical that emits beta radiation. After intravenous administration, it is taken up preferentially by osteoblastic bone metastases, where its beta decay causes DNA damage and cell death in tumor cells.
| Metabolism | Strontium-89 chloride is not metabolized; it is excreted primarily via the kidneys. The retained fraction is incorporated into the bone matrix with a biological half-life of about 50 days. |
| Excretion | Renal excretion of strontium-89; approximately 70% excreted in urine within 48 hours, with the remainder eliminated over weeks via both renal and fecal routes (12-20% fecal). |
| Half-life | Terminal elimination half-life is approximately 50.5 days (range 20-87 days). Clinical context: due to prolonged retention in bone metastases, radiobiological half-life exceeds physical half-life; therapeutic effect persists for weeks despite declining plasma levels. |
| Protein binding | Strontium-89 does not bind to plasma proteins. |
| Volume of Distribution | Initial volume of distribution approximates extracellular fluid volume (~0.3 L/kg). Ultimate distribution includes extensive bone uptake, with a functional Vd exceeding several hundred L due to long-term retention. |
| Bioavailability | 100% (intravenous administration only). |
| Onset of Action | Pain relief typically begins 7-20 days after intravenous administration. |
| Duration of Action | Duration of pain relief 3-6 months in responders; may last up to 18 months in some cases. Clinical note: effect is palliative, not curative. |
Metastron (strontium-89 chloride) is administered intravenously at a dose of 148 MBq (4 mCi) as a single injection.
| Dosage form | INJECTABLE |
| Renal impairment | Contraindicated in patients with severely impaired renal function (eGFR < 30 mL/min). For GFR 30-50 mL/min, consider dose reduction to 1-2 mCi; for GFR > 50 mL/min, no adjustment needed. |
| Liver impairment | No specific dosing adjustments based on Child-Pugh class; use caution in severe hepatic impairment due to lack of data. |
| Pediatric use | Safety and efficacy in pediatric patients have not been established; use is not recommended. |
| Geriatric use | No specific dose adjustment in elderly; monitor renal function and adjust dose as per renal guidelines since renal function may decline with age. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for METASTRON (METASTRON).
| Breastfeeding | Strontium-89 is excreted in human milk; M/P ratio not established. Due to radionuclide properties, breastfeeding is contraindicated during therapy and for at least 12 months after administration to avoid infant radiation exposure. |
| Teratogenic Risk | FDA Pregnancy Category X. Metastron (strontium-89 chloride) is contraindicated in pregnancy due to radiation exposure. Fetal risk is highest in first trimester with potential for teratogenesis, growth retardation, and carcinogenesis. In second and third trimesters, risk of fetal damage remains significant, including possible neonatal myelosuppression. Use only if benefit outweighs risk in life-threatening maternal cancer. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Pregnancy","Lactation (discontinue nursing or discontinue drug)","Pre-existing severe bone marrow suppression (e.g., platelet count < 60,000/μL or white blood cell count < 2,400/μL)","Acute or chronic renal failure (creatinine clearance < 30 mL/min)"]
| Precautions | ["Myelosuppression: Thrombocytopenia and neutropenia occur, especially in patients with compromised bone marrow reserve. Monitor blood counts regularly.","Bone marrow failure: Risk is increased in patients with advanced disease, prior chemotherapy, or radiation therapy.","Urinary excretion: Strontium-89 is excreted renally; renal impairment may increase systemic exposure.","Hypersensitivity reactions: Anaphylaxis has been reported rarely.","Pregnancy: Category D; can cause fetal harm. Women of childbearing potential should avoid pregnancy during treatment."] |
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| Fetal Monitoring | Monitor maternal CBC (platelets, WBC) weekly during therapy due to myelosuppression. During pregnancy, if used, perform fetal ultrasound to assess growth and anomalies. Postpartum, monitor neonate for signs of radiation exposure and myelosuppression. No specific fetal monitoring recommended if drug avoided in pregnancy. |
| Fertility Effects | Strontium-89 may impair fertility in both sexes due to radiation-induced gonadal damage. Ovarian and testicular function may be reduced, potentially causing oligospermia, amenorrhea, or permanent sterility. Pre-treatment fertility preservation counseling is advised for patients of childbearing potential. |