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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 sustained endogenous production of Factor IX. It is a one-time intravenous infusion.
## 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 current or historical life-threatening hemorrhage, or have repeated, serious spontaneous bleeding episodes. It is not indicated for patients with neutralizing antibodies to the AAV-Rh74var capsid.
## Adult Dosing
A single dose of 5 × 10¹¹ vector genomes per kilogram (vg/kg) of body weight administered as a slow intravenous infusion.
## Pediatric Dosing
Safety and effectiveness have not been established in pediatric patients (<18 years). Use in this population is currently not recommended.
## Dose Adjustments
* **Hepatic/Renal Impairment:** No specific adjustments provided in the prescribing information, but baseline hepatic function must be assessed, as underlying liver disease may impact outcomes or safety.
* **Weight-based:** The dose is strictly fixed at 5 × 10¹¹ vg/kg. If the patient’s weight changes between dose calculation and administration, the dose must be recalculated based on the weight on the day of infusion.
## Contraindications
* Known hypersensitivity to fidanacogene elaparvovec-dzkt or any of its components.
* Presence of neutralizing antibodies to AAV-Rh74var capsid as detected by a validated companion diagnostic test.
* Active, acute, or chronic hepatitis or active infections.
## Adverse Effects
* **Elevated Liver Enzymes:** Transient increases in ALT are common, often requiring prophylactic or reactive corticosteroid therapy.
* **Infusion-Related Reactions:** Pyrexia, nausea, vomiting, shivering, and headache.
* **Others:** Fatigue, increased creatine phosphokinase (CPK), and infusion site reactions.
## Key Drug Interactions
* **Corticosteroids:** Concomitant use is required for managing potential immune responses to the viral vector and the resulting transaminitis.
* **Hepatotoxic Agents:** Use with extreme caution as liver stress may increase the risk of therapy failure or adverse immune responses.
## Monitoring
* **Pre-infusion:** AAV-Rh74var neutralizing antibody testing.
* **Liver Function:** Weekly ALT monitoring (at minimum) for at least the first 3 months post-infusion to detect immune-mediated hepatocyte activity.
* **Factor IX Activity:** Ongoing monitoring of Factor IX activity levels to assess response and potential need for supplemental therapy during the transition period.
## Clinical Pearls
* **Corticosteroid Taper:** A tapering course of corticosteroids is standard practice to prevent the host immune system from clearing the transduced hepatocytes, which would lead to a decline in Factor IX levels.
* **Duration of Effect:** While expected to be a one-time treatment, long-term durability data are still being collected. Patients may eventually require supplemental therapy if Factor IX levels decline.
* **Patient Education:** Ensure patients understand that Factor IX therapy must be continued until the therapeutic effect of the gene therapy is confirmed by rising Factor IX levels.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice guidelines and prescribing information are subject to change. Always consult the current FDA-approved full prescribing information (PI) or institutional clinical protocols before the preparation or administration of this medication.
