Interferons are a group of naturally occurring proteins that form an essential part of the immune system. Interferons operate in two ways. Firstly, they hinder the replication process of the virus. Secondly, they enhance the body’s immune response.
They hinder the replication process by binding to receptors that are present on nearly all cell types. By doing this they prevent a virus from entering the cell and replicating within it.
Interferons enhance the immune response by stimulating the activity of immune cells and rendering virus-infected cells more susceptible to the responses of the immune system. The three types of interferon are referred to by Greek letters - alpha, beta and gamma.
In its naturally occurring form alpha interferon is produced by the body to fight infections, notably flu. It is responsible for many of the symptoms associated with flu, such as headaches, fever, and the shivers.
As a treatment for hepatitis C, interferon is synthetically produced in a laboratory and administered by injection under the skin in very high doses. It is hardly surprising that some of the usual side effects of taking interferon are actually flu-like symptoms.
Laboratory-produced standard interferon is broken down relatively fast by the body. As a result, its effectiveness decreases. This allows the hepatitis C virus to multiply between each injection. Pegylation is a process whereby a large molecule chain is attached to the interferon to slow the rate at which it is broken down. This molecule chain allows consistent levels of the drug to circulate in the body. Consequently it can maintain a consistent attack on the virus. It also means that while standard interferon needs to be taken 3 times a week, pegylated interferon only has to be injected once a week.
Two drug companies manufacture pegylated interferon. Roche Products Ltd make Pegasys (interferon alpha 2A) and MSD make PegIntron (interferon alpha 2B). They are similar, although not identical. Click on the links for more information.
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Ribavirin is a synthetic antiviral nucleoside analogue. In the treatment of hepatitis C it works very successfully with interferon but not on its own. It was originally developed as an antiviral agent for diseases that cause respiratory problems.
The possibility for it being used in conjunction with interferon was first noted in 1990. Since 1998 it has been incorporated into standard treatment for hepatitis C. Ribavirin inhibits viral growth, has anti-viral properties and interrupts the way the hepatitis C virus absorbs genetic material when it replicates.
In the majority of cases, for the treatment of hepatitis C ribavirin is used alongside interferon. Ribavirin is ineffective against hepatitis C on its own. It comes in 200mg pill or capsule form and is taken orally, twice daily, with the dose being dependent on patient weight and genotype.
The same two drug companies that make Interferon also manufacture ribavirin. Roche Products Ltd makes Copegus. MSD make Rebetol. Both drugs are essentially identical. More details can be found on their websites.