Hepatitis B Drug Resistance
Treating chronic Hepatitis B is complex, with a wide variety of medication combinations that must be tailored to each individual receiving treatment. Drug resistance is one of the primary factors complicating any attempt to rid the Hepatitis B virus from an infected person’s body. Instead of giving up on any medications that Hepatitis B could develop resistance to, patients must work closely with their physician and follow their prescription to the letter for the best chance of triumphing over this stubborn, chronic viral infection.
Treatment for chronic Hepatitis B typically uses a two-pronged approach – interferon to boost the immune system’s response to the virus and an antiviral drug to block the Hepatitis B virus from replicating.
About Drug Resistance
Hepatitis B antiviral drugs are known to develop drug resistance. The Hepatitis B virus is intelligent, and it is frequently able to escape the way antiviral drugs fight it. They do this by slightly changing their genetic material so that the drugs are no longer effective in interfering with the virus’s reproductive cycle. A virus that has mutated to become drug resistant can be especially hard to eliminate.
Experts believe there are three main ways of increasing the development of drug resistance:
- Weak Drug – Resistance is more likely to emerge if the antiviral drugs are not strong enough to prevent the virus from escaping its control.
- Dosage Mishap – If an antiviral drug is not taken as directed, such as when a person misses or forgets to take a dose, it creates a window of opportunity for the virus to gain strength and escape the drug’s control.
- Timing with Food – An antiviral drug may need to be taken with food to maximize how it is absorbed in the body. If advised to do so by a physician and/or pharmacist, taking an antiviral drug with food makes it more potent, thus making it harder for the virus to escape from the drug’s control.
Some Are More Resistant Than Others
When it comes to drug resistance, not all Hepatitis B antivirals are created equally. A list of these drugs and a brief description of their known resistance profile is described below:
- Lamivudine (Epivir-HBV) – Approved for Hepatitis B in 1998, this drug initiates drug resistance in 60 to 70 percent of people taking it after five years.
- Adefovir (Hepsera) – Approved for Hepatitis B in 2002, this drug initiates drug resistance in 29 percent of people taking it after five years.
- Entecavir (Baraclude) – Approved for Hepatitis B in 2005, this drug initiates drug resistance in 1.2 percent of treatment naïve people after six years – and 57 percent of people who are already resistant to lamivudine after six years.
- Telbivudine (Tyzeka) – Approved for Hepatitis B in 2006, this drug initiates drug resistance in 25 percent of people who are HBeAg positive after two years, and in 11 percent of people who are HBeAg negative after two years. A positive HBeAg test indicates that the virus is replicating and the infected person has high viral levels of the Hepatitis B virus. As of April 2011, the FDA approved a change in labeling telbivudine that indicates the upper limits of allowable Hepatitis B viral load due to the potential to develop drug resistance.
- Tenofovir (Viread) – Approved for Hepatitis B in 2008, this drug has a zero percent drug resistance rate after two years; but the five year drug resistance rate is not yet known.
Of the drugs available, experts recommend combining pegylated interferon (Pegasys) and the antivirals tenofovir (Viread) and entecavir (Baraclude) as the best drugs to treat HBeAg-positive or -negative patients who have never been treated before. Besides being some of the most potent antiviral drugs for fighting Hepatitis B, Viread and Baraclude have relatively low rates of drug resistance in those who are treatment naïve. If drug resistance has already occurred to one of the Hepatitis B antivirals, changes in the treatment protocol are necessary – and can become very complex.
Working under the close guidance of a physician is crucial for getting the best possible Hepatitis B treatment. If antiviral resistance has developed, another combination of drugs must be chosen that will work against the drug resistant Hepatitis B virus. Especially due to the risk of drug resistance, doctors are very careful about their Hepatitis B prescriptions – and patients need to be just as careful in following them.
http://www.hbvadvocate.org/hepatitis/factsheets_pdf/Drug%20Resistance.pdf, What Happens When Drug Resistance Develops?, Christine M. Kukka, Retrieved April 17, 2011, Hepatitis C Support Project, 2011.
http://www.hbvadvocate.org/hepatitis/Basics/HEP%20B%20BASICS%20Drug%20Resistance_10.pdf, HBV Drug Resistance, hbvadvocate.org, 2011.
http://www.hivandhepatitis.com/hep_b/news/2011/0404_2010_c.html, Telbivudine Label Adds Resistance Warning, Retrieved April 17, 2011, hivandhepatitis.com, 2011.