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# Durveqtix (fidanacogene elaparvovec-dzkt)
## Overview
Durveqtix is an adeno-associated virus vector-based gene therapy designed to deliver a functional copy of the *F9* gene to liver cells, enabling the endogenous production of Factor IX. It is a one-time infusion intended to reduce or eliminate the need for routine factor replacement therapy in patients with hemophilia B.
## Primary Indications
Treatment of adults with moderately severe to severe hemophilia B (congenital Factor IX deficiency) who are currently using Factor IX prophylactic therapy or have a history of life-threatening hemorrhage/repeated serious spontaneous bleeding episodes.
## Adult Dosing
* **Dosage:** 5 x 10¹¹ vector genomes (vg) per kilogram of body weight.
* **Administration:** Single-dose intravenous infusion at a constant rate.
* **Maximum:** There is no total dose cap specified beyond the weight-based calculation.
## Pediatric Dosing
* **Status:** Not FDA-approved for pediatric patients. Safety and efficacy in individuals under 18 years of age have not been established.
## Dose Adjustments
* No dose adjustments are permitted. The therapy is a single, weight-based dose. It cannot be re-administered.
## Contraindications
* Hypersensitivity to the active substance or any excipients.
* Active, acute, or chronic infections (specifically uncontrolled viral infections).
* Advanced hepatic fibrosis or cirrhosis (must be screened via imaging or elastography prior to administration).
## Adverse Effects
* **Most Common:** Elevation in transaminases (ALT/AST), infusion-related reactions (fever, flushing, nausea, tachycardia), and headache.
* **Serious:** Immune-mediated hepatotoxicity (triggered by the viral vector).
## Key Drug Interactions
* **Corticosteroids:** Concomitant use is often required as a prophylactic or therapeutic measure to manage immune-mediated transaminitis following infusion.
* **Hepatotoxic Agents:** Avoid or use with extreme caution other medications known to cause liver injury, as these may complicate the monitoring of liver enzyme elevations associated with the therapy.
## Monitoring
* **Liver Enzymes (ALT):** Must be monitored weekly for at least the first 3 months post-infusion to detect and manage immune-mediated hepatitis.
* **Factor IX Activity:** Periodic monitoring of Factor IX activity levels is required to determine the therapeutic response and the potential need for supplemental prophylaxis during the transition period.
* **Viral Vector Shedding:** Follow local institutional protocols regarding monitoring for potential viral shedding in bodily fluids.
## Clinical Pearls
* **Liver Enzyme Management:** If ALT levels rise, prompt initiation of a corticosteroid taper is standard to mitigate immune response against the transduced hepatocytes.
* **Pre-screening:** All patients must be screened for pre-existing neutralizing antibodies to AAVRh74 capsid. Patients with high titers may not be candidates for therapy.
* **Timing:** Patients may require supplemental Factor IX prophylaxis for several weeks post-infusion until stable therapeutic levels are achieved.
* **Efficacy:** The clinical goal is the production of functional Factor IX; however, individual expression levels are variable.
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**Educational Disclaimer:** This information is for educational purposes only. Gene therapy products are highly complex and subject to specialized risk evaluation and mitigation strategies (REMS). Always verify the latest prescribing information, package inserts, and institutional protocols before clinical administration.
