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Hepatitis C Viral RNA NS3 Drug Resistance

Test code(s) 90924

Question 1. What are hepatitis C virus (HCV) NS3 protease inhibitors?

NS3 protease inhibitors are antiviral drugs. They are classified as direct acting agents (DAAs) and work by inhibiting the HCV NS3a protease.1-2 Clinical studies have shown that when NS3 protease inhibitors are combined with other DAAs, a high proportion of patients achieve a sustained virologic response (SVR).3

 

Question 2. Which NS3 protease inhibitors are approved for clinical use?

Victrelis® (Boceprevir) and Incivek® (telaprevir) were approved by the FDA in 2011 for the treatment of HCV genotype 1 patients.4,5 Boceprevir and telaprevir are no longer recommended for clinical use in the U.S.

Olysio® (simeprevir) was approved by the FDA in 2013 and Viekira Pak® (dasabuvir, ombitasvir, paritaprevir, ritonavir) was approved in 2014 for the patients with HCV genotype 1.6,7 Zepatier® (grazoprevir and elbasvir was approved in 2016 for use in genotypes 1 and 4.8 Additional NS3 inhibitors are currently under FDA review or are undergoing clinical trials.

 

 

 

Question 3. Which method is used to test for HCV NS3 inhibitor resistance?

Quest Diagnostics uses reverse transcription polymerase chain reaction (PCR) and DNA sequencing of HCV genotype 1 NS3 codons 1 to 181. This method detects protease inhibitor resistance-associated variants (RAVs), such as the R155K mutation in HCV genotype 1a and the A156T mutation in HCV genotype 1b. These and other mutations result in resistance to some or all NS3 protease inhibitors.3,6-9

 

Question 4. What is the Q80K polymorphism?

The Q80K polymorphism is a naturally occurring amino acid substitution of glutamine to lysine at NS3 codon 80. It is found in 30% to 50% of HCV genotype 1a infected patients and in 0.5% of genotype 1b patients.3,6 Clinical studies have shown that when cirrhotic patients with HCV genotype 1a have this polymorphism at baseline, the efficacy of simeprevir in combination with sofosbuvir is substantially reduced.3,6 Consequently, alternative therapy should be considered for such patients.3,6

 

Question 5. Is NS3 genotype testing required before prescribing an NS3 protease inhibitor-containing antiviral regimen?

NS3 genotype testing is strongly recommended before prescribing simeprevir for patients with cirrhosis and HCV genotype 1a infection or for patients who urgently require retreatment.3,6 Alternative therapy should be considered for these patients when genotype testing reveals presence of the Q80K polymorphism.3,6

 

Question 6. What is the recommended HCV genotype 1 RNA viral load for NS3 protease resistance testing?

We recommend specimens being submitted for NS3 resistance testing have an HCV RNA level of at least 1,000 IU/mL. The assay may fail at lower viral loads.

 

Question 7. How are HCV genotype 1 NS3 protease drug resistance test results reported?

 

Example 1

     

HCV NS3 Subtype: 1b

 

Grazoprevir Resistance: NOT PREDICTED

Paritaprevir Resistance: NOT PREDICTED

Simeprevir Resistance: NOT PREDICTED

MUTATIONS DETECTED: NONE

 
         

Example 2

     

HCV NS3 Subtype: 1a

 

Grazoprevir Resistance: NOT PREDICTED

Paritaprevir Resistance: NOT PREDICTED

Simeprevir Resistance: PROBABLE

MUTATIONS DETECTED: Q80K

 
         

Example 3

     

HCV NS3 Subtype: 1a

 

Grazoprevir Resistance: NOT PREDICTED

Paritaprevir Resistance: PROBABLE

Simeprevir Resistance: PROBABLE

MUTATIONS DETECTED: R155K

 

 

 

 

 

References
  
  1. Rupp D, Bartenschlager R. Targets for antiviral therapy of hepatitis C. Semin Liver Dis. 2014;34:9-21.
  2. Pawlotsky JM. New hepatitis C virus (HCV) drugs and the hope for a cure:concepts in anti-HCV drug development. Semin Liver Dis. 2014;34:22-29.
  3. American Association for the Study of Liver Diseases (AASLD) and Infectious Diseases Society of America (IDSA). Recommendations for testing, managing, and treating hepatitis C. http://www.hcvguidelines.org/. Accessed July 25, 2016.
  4. Boceprevir [package insert]. Whitehouse Station, NJ: Schering Corporation; 2011. http://www.accessdata.fda.gov/drugsatfda_docs/label/2011/202258lbl.pdf.
  5. Telaprevir [package insert]. Cambridge, MA: Vertex Pharmaceuticals Incorporated; 2011. http://www.accessdata.fda.gov/drugsatfda_docs/label/2011/201917lbl.pdf.
  6. Simeprevir [package insert]. Titusville, NJ: Janssen Therapeutics; 2013. https://www.olysio.com/shared/product/olysio/prescribing-information.pdf
  7. VIEKIRA PAK® [package insert]. Chicago, IL: Abbvie Incorporated; 2014. http://www.rxabbvie.com/pdf/viekirapak_pi.pdf
  8. Zepatier® [package insert]. Kenilworth, NJ: Merck; 2016. https://www.merck.com/product/usa/pi_circulars/z/zepatier/zepatier_pi.pdf
  9. Lontok, E, Harrington, P, Howe, A, et al. Hepatitis C virus drug resistance-associated substitutions: State of the art summary. Hepatology. 2015;62:1623-1632.
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
Document FAQS.132 Version: 4
Version 4 effective 08/22/2016 to present
Version 3 effective 11/24/2015 to 08/22/2016
Version 2 effective 07/08/2015 to 11/23/2015
Version 1 effective 03/12/2014 to 07/07/2015
Version 0 effective 01/09/2014 to 03/11/2014