Strontium Chloride (Sr-89 Chloride)

Usage

Strontium-89 chloride (Sr-89) is a radiopharmaceutical indicated for the palliation of bone pain in patients with painful skeletal metastases, particularly those arising from prostate cancer. It is specifically used when conventional therapies, such as external beam radiotherapy, chemotherapy, hormone therapy, and analgesics, have proven ineffective or are no longer providing adequate relief. Its use is limited to patients with confirmed bone metastases.

• Pharmacological Classification: Radiopharmaceutical, bone pain palliative
• Mechanism of Action: Sr-89 mimics calcium and is preferentially taken up by areas of active bone formation, especially in metastatic bone lesions where osteoblast activity is high. It emits beta radiation, delivering localized radiation to these areas. The exact mechanism of pain relief is unclear, but it is thought to involve the disruption of pain-producing enzymes or suppression of tumor growth within the bone.

Alternate Names

• Strontium Chloride Sr-89
• Strontium-89
• SR-89
• Sr89
• Metastron (former brand name, now discontinued in some regions)

How It Works

• Pharmacodynamics: Sr-89 targets areas of increased bone turnover, delivering beta radiation to bone metastases. This localized radiation reduces pain, potentially by inhibiting tumor growth, disrupting the production of pain-inducing factors, and reducing osteoclast activity.
• Pharmacokinetics:
  • Absorption: Administered intravenously, achieving immediate systemic circulation.
  • Distribution: Selectively accumulates in bone mineral with a preference for metastatic bone lesions.
  • Metabolism: Decays by beta emission to stable Yttrium-89 with a physical half-life of 50.5 days.
  • Elimination: Primarily excreted through the kidneys (approximately 67%) and in feces (approximately 33%). Renal clearance is the major route of elimination.

Dosage

Standard Dosage

Adults:

• The recommended dose is 148 MBq (4 mCi) as a slow intravenous injection over 1-2 minutes.
• Alternatively, a dose of 1.5 - 2.2 MBq/kg (40-60 µCi/kg) body weight can be used.
• Repeat administrations should be determined on a case-by-case basis, considering patient response, current symptoms, and hematologic status. They are generally not recommended at intervals of less than 90 days.

Children:

• Safety and efficacy have not been established in children below the age of 18 years.

Special Cases:

• Elderly Patients: No specific dose adjustments are recommended based on age.
• Patients with Renal Impairment: Careful consideration of the administered dose is required due to the potential for increased radiation exposure. Dosage reduction may be warranted.
• Patients with Hepatic Dysfunction: No specific adjustments are typically necessary, as hepatic metabolism is not the primary route of elimination.
• Patients with Comorbid Conditions: Pre-existing hematologic conditions (low platelet or white blood cell counts) warrant careful consideration.

Clinical Use Cases

Sr-89 is primarily used for palliation of bone pain from skeletal metastases. It’s not typically used in the specific contexts of intubation, surgical procedures, mechanical ventilation, intensive care unit (ICU) use, or emergency situations.

Dosage Adjustments

• Dose modifications are needed in cases of renal impairment, with consideration given to the degree of dysfunction.
• Patients with pre-existing bone marrow suppression or blood disorders require close hematologic monitoring and potential dose reduction.

Side Effects

Common Side Effects

• Mild, transient increase in bone pain 36-72 hours after injection
• Flushing (especially with rapid injection)
• Decreased platelet and white blood cell counts (myelosuppression)

Rare but Serious Side Effects

• Severe myelosuppression (leukopenia, thrombocytopenia)
• Infections due to immunosuppression
• Secondary malignancies (rare)

Long-Term Effects

• The long-term effects of Sr-89 are not extensively studied due to the nature of the patients treated and the single or limited dose administrations. The possibility of secondary malignancies exists but is considered low.

Adverse Drug Reactions (ADR)

• Severe myelosuppression requiring transfusion support
• Serious infections requiring hospitalization or intensive care

Contraindications

• Pregnancy
• Breastfeeding
• Hypersensitivity to Sr-89 chloride

Drug Interactions

• Medications affecting bone marrow function may exacerbate myelosuppression.
• There are numerous potential drug interactions (over 200) documented, many with limited clinical significance. Consult a comprehensive drug interaction database for specific interactions.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: D (positive evidence of human fetal risk)
• Sr-89 is contraindicated in pregnancy due to the risk of fetal harm from radiation exposure.
• Sr-89 is contraindicated during breastfeeding because it is likely excreted in breast milk, posing a risk to the infant.

Drug Profile Summary

• Mechanism of Action: Targets bone metastases, emitting beta radiation for pain palliation.
• Side Effects: Myelosuppression, transient increased bone pain, flushing.
• Contraindications: Pregnancy, breastfeeding, hypersensitivity.
• Drug Interactions: Numerous potential interactions, primarily related to myelosuppression.
• Pregnancy & Breastfeeding: Contraindicated.
• Dosage: 148 MBq IV or 1.5-2.2 MBq/kg, repeated doses not recommended within 90 days.
• Monitoring Parameters: Blood counts (WBC, platelets), renal function.

Popular Combinations

Sr-89 is not commonly used in combination with other radiopharmaceuticals. It is usually reserved for patients who have not responded to other pain management strategies, including chemotherapy, hormone therapy, and analgesics.

Precautions

• Verify patient identity and dose before administration due to radioactivity.
• Monitor blood counts before, during, and after treatment.
• Use caution in patients with renal impairment.
• Advise women of childbearing potential to avoid pregnancy.
• Provide patients with post-administration instructions regarding minimizing radiation exposure to others.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Strontium Chloride (Sr-89)?

A: The recommended dose is 148 MBq (4 mCi) IV or 1.5-2.2 MBq/kg. Repeat doses are generally not given within 90 days.

Q2: How is Sr-89 administered?

A: Sr-89 is administered as a slow intravenous injection over 1-2 minutes.

Q3: What is the primary indication for Sr-89?

A: Palliation of bone pain from skeletal metastases.

Q4: What are the most common side effects of Sr-89?

A: Transient increased bone pain, myelosuppression (decreased blood counts), and flushing.

Q5: Is Sr-89 safe to use in pregnant or breastfeeding women?

A: No, Sr-89 is contraindicated in both pregnancy and breastfeeding.

Q6: How long does it take for Sr-89 to provide pain relief?

A: Pain relief typically occurs 7-20 days after administration.

Q7: How often can Sr-89 be administered?

A: Repeat administrations are generally not recommended at intervals of less than 90 days.

Q8: Are there any specific precautions for handling Sr-89?

A: Yes, appropriate safety measures must be taken to minimize radiation exposure to healthcare personnel.

Q9: What monitoring is necessary during Sr-89 therapy?

A: Regular blood count monitoring (especially WBC and platelets) is essential. Renal function should also be monitored.

Q10: What should patients be advised after receiving Sr-89?

A: Patients should receive instructions regarding precautions to minimize radiation exposure to others, including careful handling of bodily fluids and proper waste disposal.