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# Arsil (Arsenic Trioxide)
## Overview
Arsenic trioxide is an antineoplastic agent that induces differentiation and apoptosis in target cells. It is primarily used in hematologic malignancies, specifically affecting the degradation of the PML-RARα fusion protein in acute promyelocytic leukemia (APL).
## Primary Indications
* Relapsed or refractory acute promyelocytic leukemia (APL) characterized by the presence of the t(15;17) translocation or PML/RARα gene expression.
* First-line treatment of APL (in combination with all-trans retinoic acid).
## Adult Dosing
* **Induction:** 0.15 mg/kg IV daily until bone marrow remission (maximum 60 days).
* **Consolidation:** 0.15 mg/kg IV daily for 25 doses over a period of up to 5 weeks.
## Pediatric Dosing
* **Safety/Efficacy:** Established for children $\ge$ 5 years of age.
* **Dosing:** Same as adult dosing (0.15 mg/kg). Note: Dosing for patients <5 years is not well-established and generally follow institutional protocols based on body surface area (BSA) or weight-adjusted oncology guidelines.
## Dose Adjustments
* **Renal Impairment:** No formal guidelines; use with caution.
* **Hepatic Impairment:** No formal guidelines; monitor closely for toxicity.
* **QT Prolongation:** If QTc > 500 msec, withhold treatment, correct electrolyte imbalances (K+, Mg2+), and resume at 50% dose once QTc returns to < 460 msec.
## Contraindications
* Hypersensitivity to arsenic trioxide.
* Presence of QTc prolongation prior to initiation.
## Adverse Effects
* **APL Differentiation Syndrome:** Potentially fatal; characterized by fever, dyspnea, weight gain, pulmonary infiltrates, and pleural/pericardial effusions.
* **Cardiovascular:** QTc prolongation, Torsades de pointes, atrial fibrillation.
* **Hematologic:** Leukocytosis, hemorrhage.
* **Common:** Fatigue, peripheral neuropathy, hyperglycemia, elevated liver enzymes.
## Key Drug Interactions
* **QT-Prolonging Agents:** Avoid concurrent use of drugs known to prolong the QT interval (e.g., anthracyclines, ondansetron, certain antipsychotics, quinolones).
* **Diuretics:** May increase risk of arrhythmias by causing hypokalemia or hypomagnesemia.
## Monitoring
* **ECG:** Perform baseline, weekly (at least twice weekly during induction), and as clinically indicated to monitor QTc.
* **Electrolytes:** Maintain potassium > 4.0 mEq/L and magnesium > 1.8 mg/dL.
* **Labs:** CBC with differential, LFTs, creatinine, and coagulation profile (at least twice weekly).
* **Clinical:** Monitor closely for signs of Differentiation Syndrome (respiratory status, weight, fluid balance).
## Clinical Pearls
* **Differentiation Syndrome management:** If symptoms arise, initiate dexamethasone (10 mg IV BID) immediately and continue for at least 3 days or until resolution.
* **Infusion:** Administer IV over 1-2 hours; may extend to 4 hours if systemic vasomotor reactions occur.
* **Leukocytosis:** Often managed with hydroxyurea during the induction phase if the WBC count rises significantly.
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*Disclaimer: This information is for educational purposes only. Clinical practice varies by institution and patient-specific factors. Always consult the latest FDA-approved prescribing information, institutional protocols, and a clinical pharmacist before prescribing or administering medication.*
