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Viekira Pak Dosage, Side Effects, Cost, and Prescribing Information for Hepatitis C Category: Hepatitis by - January 14, 2015 | Views: 15896 | Likes: 0 | Comment: 0  

Viekira Pak for HCV

Brand Name: Viekira Pak
Generic Name: ombitasvir, paritaprevir, and ritonavir tablets; dasabuvir tablets

Medication Class: Direct-Acting antiviral agent
Similar Drugs: Sovaldi (sofosbuvir), Harvoni (ledipasvir/sofosbuvir)OlysioVictrelis, Incivek
Manufacturer: Abbvie Inc.
FDA Approval Date: December 2014

What is Viekira Pak and its mechanism of action?

Hepatitis C virus (HCV) infects the human liver, causing acute and chronic hepatitis. Acute hepatitis C virus infection occurs usually within the first six months of exposure to the virus, and it can resolve on its own. However, 75% to 85% of those who become infected with hepatitis C virus develop chronic infection. Chronic hepatitis C virus infection is a long-term disease that can last a lifetime. When the liver constantly tries to get rid of the virus, it remains inflamed and can lead to liver problems such as cirrhosis or liver cancer. Many patients with chronic hepatitis C do not show any symptoms until the liver is damaged. Approximately 15,000 patients die each year from hepatitis C-related liver disease in the United States. Therefore, appropriate treatment of chronic hepatitis C virus infection is required.

Viekira Pak is a combination product for treating HCV infection. It consists of 3 direct-acting antiviral agents (ombitasvir, paritaprevir, and dasabuvir) with different mechanisms of action. Each agent targets hepatitis C virus at different steps in the viral life cycle. Viekira also contains ritonavir which boosts blood levels of paritaprevir. Usually, 600 mg taken twice daily of ritonavir is used to treat adult HIV patients. Viekira Pak only contains 50 mg of ritonavir which is much smaller amount than the dose for HIV treatment. The ritonavir in Viekira Pak act is a potent CYP3A4 liver enzyme inhibitor. In other words, ritonavir slows down the breakdown of paritaprevir in the liver so that paritaprevir can stay in the body at a higher concentration to fight against HCV better.

Ombitasvir inhibits a viral protein called NS5A which plays a key role in hepatitis C virus RNA replication. Without proper RNA replication, the virus is unable to multiply and regenerate. Paritaprevir blocks a viral structure called NS3/4A protease which is a required component for proper viral replication. By blocking this structure, the virus is unable to mature and replicate. Dasabuvir blocks a viral structure called NS5B palm polymerase which is also an essential component for replication of hepatitis C virus. By blocking multiple steps in the viral life cycle with these three active agents, hepatitis C virus replication is reduced significantly and sustained virologic response (SVR) is achieved.

What is Viekira Pak used for treating?

Viekira is used with or without ribavirin for treating patients with genotype 1 chronic hepatitis C virus infection including those with compensated cirrhosis. Note that there are several types (genotypes) of hepatitis C virus. They are divided into 6 distinct genotypes with multiple subtypes. Hepatitis C genotype 1 virus is the most common type in the United States and more difficult to treat than genotype 2 and 3.

How effective is Viekira Pak?

FDA approved the safety and effectiveness of Viekira based on the 6 clinical trials including 2308 patients with genotype 1 chronic HCV infection, some with cirrhosis.

The first study included treatment naive (no prior HCV treatment received) patients with genotype 1a and 1b chronic HCV infection without cirrhosis. It compared the effectiveness of Viekira Pak in combination with ribavirin versus placebo (harmless sugar pill). The second study included patients with genotype 1a and 1b chronic HCV infection who were prior relapsed, partial responders, or prior non-responders to pegIFN/RBV treatment, and without cirrhosis. This trial also studied the effectiveness of Viekira Pak with ribavirin versus placebo. The third study included patients with genotype 1b chronic HCV infection that are treatment-experienced but without cirrhosis. This trial studied the effectiveness of Viekira Pak with ribavirin versus just Viekira Pak. The fourth study included patients with genotype 1b chronic HCV infection that are treatment naive without cirrhosis. This trial also studied the effectiveness of Viekira Pak with ribavirin versus Viekira Pak only. The fifth study included patients with genotype 1a chronic HCV infection that are treatment naive without cirrhosis. This trial studied the effectiveness of Viekira Pak with ribavirin versus Viekira Pak alone. Lastly, the sixth study included patients with genotype 1a and 1b chronic HCV infection that are treatment naive and treatment-experienced with cirrhosis. This trial studied the effectiveness of Viekira Pak in combination with ribavirin for 12 weeks of treatment versus 24 weeks.

In these 6 clinical trials, ombitasvir, paritaprevir, ritonavir dose was 25/150/100 mg taken by mouth once daily for 12 weeks and dasabuvir was dosed at 250 mg taken by mouth twice daily for 12 weeks. (Except the last clinical trial where the duration of therapy was different). For patients who received ribavirin, it was dosed at 1000 mg by mouth daily if the patient weighs less than 75kg, or at 1200 mg by mouth daily if the patient weighed 75kg or more.

The studies measured the cure rate of each patient based on whether or not HCV was detectable in the blood at least 12 weeks after the end of treatment. If the HCV level was below the lower limit of quantification (LLOQ), the patient was considered successfully treated. If the HCV level was above LLOQ, the patient was considered as treatment failure. Overall, the 6 clinical trials showed that the cure rate of patients that were treated with Viekira Pak ranged from 91% to 100% throughout the trials. For example, the first trial showed that 96% of patients who were treated with Viekira Pak plus ribavirin had treatment success and 4% of them had a relapse or treatment failure. For the complete information on all 6 clinical trials, please refer to the Viekira Pak Prescribing Information.

What are side effects of Viekira?

The most common side effects of Viekira include tiredness, nausea, itching, skin reactions such as redness or rash, sleep problems, and feeling weak. More serious adverse reactions include anemia, hyperbilirubinemia, ALT elevation, and muscle spasm based on the clinical trials with Viekira Pak. More adverse reactions may be added once studied with post-market research.

What is the dosage of Viekira?

Viekira Pak contains 2 tablets. The pink tablet contains 12.5 mg of ombitasvir, 75 mg of paritaprevir, and 50 mg of ritonavir. The beige tablet contains 250 mg of dasabuvir.

The recommended dose is 2 pink tablets once in the morning and one beige tablet twice daily with meals.

Viekira Pak can be used in combination with ribavirin for certain patient populations such those with genotype 1a with or without cirrhosis, or genotype 1b with cirrhosis. The combination of Viekira Pak and ribavirin should be used for 12 weeks except in patients with genotype 1a and cirrhosis. Patients with genotype 1a and cirrhosis should be treated for 24 weeks.

What if a dose is missed?

If a pink tablet (combination of ombitasvir, paritaprevir, and ritonavir) is missed the prescribed dose should be taken within 12 hours.  If more than 12 hours has passed, the missed dose should not be taken and the patient should take the next scheduled dose.

If a beige tablet (dasabuvir) is skipped the prescribed dose should be taken within 6 hours. If more than 6 hours has passed, the missed dose should not be taken and the patient should take the next dose scheduled dose.

What are Viekira drug interactions?

Paritaprevir and ritonavir are primarily metabolized (broken down) by liver enzymes called cytochrome P450 (CYP450) enzymes. Dasabuvir is primarily metabolized by CYP2C8 liver enzymes, and ombitasvir is primarily metabolized via amide hydrolysis with minor CYP450 enzyme metabolism. 

The blood concentration of Viekira Pak may increase if co-administered with drugs that are strong inhibitors of CYP3A4, CYP2C8, and P-gp. The efficacy of Viekira Pak may be reduced if co-administered with drugs that are strong inducers of CYP3A4 and CYP2C8.

The drug components in Viekira Pak, especially ritonavir, affect several enzyme pathways that metabolize several types drugs. Therefore, Viekira Pak may increase or decrease the efficacy of other drugs.

The following drugs should not be combined with Viekira Pak. This is not a complete list of drugs that interact with components of Viekira Pak. Please refer to the Prescribing Information or check with a pharmacist to see if there is an interaction with a medication.

  • Alfuzosin, lovastatin, simvastatin are metabolized by CYP3A4 enzymes. If co-administered with Viekira Pak the blood concentrations of these drugs may increase leading to increased side effects.
  • Carbamazepine, phenytoin, and phenobarbital are potent inducers and substrates of CYP3A4. If co-administered with Viekira Pak, the blood concentration of Viekira Pak is expected to decrease.
  • Gemfibrozil is a potent inhibitor of CYP2C8. If co-administered with Viekira Pak the blood concentration of dasabuvir may increase and cause potential dasabuvir induced QT prolongation (abnormal heart rhythm.
  • Combining Viekira Pak with sildenafil (Viagra, Revatio) may increase side effects of sildenafil such as visual disturbance, hypotension, priapism (abnormal erection), and fainting.
  • Triazolam and midazolam blood levels may increase significantly when combined with Viekira Pak, leading to increased sedation or respiratory depression.
  • St. John’s Wort may decrease blood levels of ombitasvir, paritaprevir, and ritonavir, reducing the effect of Viekira Pak. 

What are warnings and precautions for Viekira?

Alanine transaminase (ALT) is one of the most abundant liver enzymes and it is used to measure liver function. In clinical trials of Viekira, some patients experienced ALT elevations during the first 4 weeks of treatment and a decline afterward. Liver function should be monitored during the first 4 weeks of therapy.

ALT elevations were more frequent in women using estrogen-containing products. Therefore, any estrogen-containing products should be discontinued prior to Viekira treatment. Estrogen products may be restarted 2 weeks after the completion of the treatment.

Viekira Pak is should not be used by patients with severe liver disease due to the risk of potential toxicity.

Can pregnant women use Viekira?

Viekira is in pregnancy category B. There were no clinical studies conducted with Viekira Pak in pregnant women. However, animal reproduction studies showed that there was no evidence of teratogenicity with ombitasvir, paritaprevir, ritonavir, or dasabuvir at exposures higher than recommended clinical dosage. Viekira Pak should be used during pregnancy only if the benefit outweighs the risks.

If Viekira Pak is used in combination with ribavirin, the combination of ribavirin plus Veikira Pak is contraindicated in pregnant women and in men whose female partners are pregnant.

What is the cost of Viekira?

The estimated retail price of Viekira is about $9,100 per Pak.

Where to find cost assistance for Viekira

There is a Viekira patient assistance program for those with or without insurance. Find out whether your insurance covers Viekira Pak.

References

CDC Hepatitis C FAQs  

Prescribing Information of Viekira Pak

 
 

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