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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 *FIX* gene to the liver. It provides sustained endogenous production of Factor IX (FIX) in patients with Hemophilia B, potentially eliminating the need for routine prophylactic factor replacement therapy.
## Primary Indications
Treatment of adults with moderate to severe Hemophilia B (congenital Factor IX deficiency) who are currently using Factor IX prophylaxis therapy, or have current or historical life-threatening hemorrhage, or have repeated, serious spontaneous bleeding episodes. It is not indicated for patients with neutralizing antibodies to AAVRh74 capsid.
## Adult Dosing
The recommended dose is 5 x 10¹¹ vector genomes (vg) per kilogram of body weight, administered as a single, one-time intravenous infusion.
## Pediatric Dosing
Safety and effectiveness in pediatric patients (younger than 18 years) have not been established. Use in patients under 18 is not currently recommended.
## Dose Adjustments
No dose adjustments are permitted. The therapy consists of a fixed, one-time dose based on patient weight. Renal or hepatic impairment adjustments have not been studied; consult institutional guidelines for patients with pre-existing hepatic disease, as baseline liver function must be stable before administration.
## Contraindications
Hypersensitivity to the active substance or any excipients. Presence of neutralizing antibodies to AAVRh74 capsid, as determined by an FDA-approved or validated companion diagnostic test.
## Adverse Effects
Common adverse events include elevated transaminases (ALT/AST), infusion-related reactions (headache, nausea, fatigue, pyrexia), and transient increase in clotting factor levels above physiological ranges. There is a potential, theoretical risk of malignancy due to vector DNA integration.
## Key Drug Interactions
Corticosteroids are used concurrently to manage immune responses to the vector. Avoid other hepatotoxic drugs or agents that may affect liver function during the peri-infusion period, as this may complicate the monitoring of transaminase elevations.
## Monitoring
Baseline and weekly (or more frequent) monitoring of ALT/AST levels is required for at least the first 3 months post-infusion to detect immune-mediated hepatotoxicity. Monitor Factor IX activity levels periodically to assess therapeutic response. Long-term monitoring (up to 15 years) is required to evaluate safety and durability of the transgene.
## Clinical Pearls
- **Immune Prophylaxis:** Patients must initiate a prophylactic corticosteroid regimen (typically tapering over 12+ weeks) starting prior to infusion to manage potential immune response to the AAV capsid, which can lead to loss of factor expression.
- **Factor Replacement:** Patients should be transitioned off prophylactic factor replacement therapy according to clinical stability; however, have factor replacement available for potential breakthrough bleeds in the early post-infusion phase if Factor IX levels have not reached target.
- **Hepatotoxicity:** Elevation of ALT/AST is common and reflects the immune-mediated destruction of transduced hepatocytes; immediate initiation/escalation of corticosteroids is critical if transaminases rise.
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**Educational Disclaimer:** This information is for educational purposes for healthcare professionals and does not replace professional clinical judgment. Always verify the most current prescribing information, institutional protocols, and FDA/EMA labels before administration. Clinical practice may vary based on local guidelines and patient-specific factors.
