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# Durveqtix (fidanacogene elaparvovec)
## Overview
Durveqtix (fidanacogene elaparvovec) is an adeno-associated virus vector-based gene therapy indicated for the treatment of adults with moderately severe to severe hemophilia B. It serves as a one-time infusion designed to deliver a functional F9 gene to the liver to induce endogenous production of Factor IX.
## Primary Indications
Treatment of adults (≥18 years) with moderately severe to severe hemophilia B (Factor IX activity ≤ 2%) who currently use Factor IX prophylactic therapy or have current or historical life-threatening hemorrhage or repeated, serious spontaneous bleeding episodes. It is not indicated for patients with neutralizing antibodies to AAVRh74.
## Adult Dosing
The recommended dose is a single intravenous infusion of **5 x 10¹¹ vector genomes per kilogram (vg/kg)**.
## Pediatric Dosing
Safety and efficacy have not been established in patients younger than 18 years. Use in the pediatric population is currently not recommended.
## Dose Adjustments
No dose adjustments are required based on weight or hepatic function beyond the calculated **5 x 10¹¹ vg/kg**.
## Contraindications
* Patients with known hypersensitivity to the active substance or any excipients.
* Patients with pre-existing antibodies to the AAVRh74 capsid (as determined by a validated clinical trial assay).
## Adverse Effects
* **Most Common:** Elevation in liver enzymes (ALT/AST), infusion-related reactions (pyrexia, chills, nausea), headache, and fatigue.
* **Serious:** Potential risk of hepatotoxicity; theoretical risk of insertional mutagenesis (though not observed in clinical trials to date).
## Key Drug Interactions
There are no formal clinical drug interaction studies for fidanacogene elaparvovec. Caution should be exercised when co-administering with hepatotoxic agents or drugs known to affect liver function. Corticosteroids (e.g., prednisone or prednisolone) are standardly utilized during the post-infusion period to manage immune responses.
## Monitoring
* **Liver Enzymes:** Monitor ALT levels weekly for at least 3 months post-infusion to detect and manage immune-mediated hepatotoxicity.
* **Factor IX Activity:** Monitor Factor IX activity levels routinely post-infusion.
* **Immunogenicity:** Monitor for loss of therapeutic effect, which may indicate the development of neutralizing antibodies.
## Clinical Pearls
* **Corticosteroid Prophylaxis:** Patients must initiate a prophylactic tapering course of corticosteroids (or equivalent immunosuppression) starting shortly after infusion to prevent or suppress immune-mediated destruction of transduced hepatocytes (indicated by rising ALT).
* **Factor IX Replacement:** Patients may require continued Factor IX replacement therapy in the initial weeks post-infusion until transgene expression reaches therapeutic levels.
* **Irreversibility:** As a one-time gene therapy, this intervention is irreversible. Patients must be counseled on the long-term, currently unknown, risks of the therapy.
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Prescribing information, dosing, and safety protocols can change. Always verify the most current prescribing information (package insert) and institutional guidelines before administering gene therapy products.
