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# Durveqtix (fidanacogene elaparvovec-dzkt)
## Overview
Durveqtix is an adeno-associated virus (AAV) vector-based gene therapy designed to deliver a functional copy of the *F9* gene to hepatocytes, enabling sustained endogenous production of Factor IX (FIX) in patients with Hemophilia B. It is a one-time intravenous infusion.
## Primary Indications
Treatment of adults (≥18 years) with moderate-to-severe hemophilia B (congenital Factor IX deficiency) who are currently using Factor IX prophylactic therapy, or have current or historical life-threatening hemorrhage, or have repeated, serious spontaneous bleeding episodes.
## Adult Dosing
The recommended dose is **5 x 10¹¹ vector genomes (vg) per kilogram of body weight**, administered as a single intravenous infusion.
## Pediatric Dosing
Safety and effectiveness in pediatric patients (younger than 18 years) have not been established. Use in this population is not recommended.
## Dose Adjustments
* **Renal/Hepatic Impairment:** No formal dosage adjustments are provided. However, baseline liver function must be clinically stable prior to administration due to the vector's hepatotropism.
* **Patient Weight:** Dose must be calculated based on the patient's actual body weight at the time of infusion.
## Contraindications
* Known hypersensitivity to fidanacogene elaparvovec-dzkt or any of its components.
* Active, uncontrolled acute infection (systemic).
* Known advanced liver fibrosis or cirrhosis (e.g., evidenced by imaging or elastography).
## Adverse Effects
* **Most Common:** Increased hepatic transaminases (ALT/AST), infusion-related reactions (pyrexia, chills, tachycardia, blood pressure fluctuations), and nausea.
* **Serious:** Potential for hepatotoxicity requiring immunosuppression; potential for development of Factor IX inhibitors (neutralizing antibodies).
## Key Drug Interactions
The use of corticosteroids is typically required post-infusion to manage immune responses to the viral capsid. Avoid concomitant use of hepatotoxic agents. Consult current prescribing information regarding live vaccinations, as immunosuppression protocols post-infusion may modulate immunization efficacy and safety.
## Monitoring
* **Liver Enzymes:** Monitor ALT/AST levels weekly for at least the first 3 months post-infusion to screen for immune-mediated hepatotoxicity.
* **Factor IX Activity:** Monitor plasma Factor IX activity levels periodically to ensure therapeutic range.
* **Inhibitor Screening:** Monitor for the development of neutralizing antibodies if clinical efficacy wanes or spontaneous bleeds recur.
## Clinical Pearls
* **Prophylactic Immunosuppression:** Patients are typically started on a tapering course of oral corticosteroids (e.g., prednisone) beginning shortly after infusion to prevent or mitigate immune-mediated clearance of the transduced hepatocytes.
* **Hepatic Safety:** Patients with pre-existing, poorly controlled liver disease are at higher risk for complications; rigorous pre-screening is required.
* **Product Handling:** This is a gene therapy product; handle according to institutional biosafety guidelines for viral vectors.
* **Uncertainty:** Long-term durability of transgene expression remains under study; patients may eventually require rescue therapy with Factor IX concentrates if FIX levels decline over time.
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**Educational Disclaimer:** This information is for educational purposes only. Always consult the current FDA-approved full prescribing information (Package Insert) and your institution's specific clinical protocols before ordering or administering this therapy. Do not use this as a substitute for clinical judgment.
