Interferons and ribavirin

Interferons are a group of naturally occurring proteins that form an essential part of the immune system. Interferons operate in two primary ways, firstly they directly hinder the replication process of the virus and secondly they enhance the immune response. They hinder the replication process by binding to receptors that are present on nearly all cell types and preventing a virus from entering the cell and replicating within it. They enhance the immune response by stimulating 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, and is responsible for many of the symptoms associated with flu, such as headaches, fever, shivering (it is often the case that it is the bodys reaction rather than a disease itself that makes you feel ill). As a treatment for hepatitis C, it is synthetically produced in a laboratory and administered by injection under the skin in doses considerably higher than occur naturally. So it is hardly surprising that some of the usual side effects of taking interferon are flu-like symptoms.

Laboratory-produced standard interferon is broken down relatively fast by the body. As a result, its effectiveness decreases, allowing the hepatitis C virus to multiply in between injections. 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 is made up of essentially inactive chemicals and does not change the basic nature of the interferon but it allows consistent levels of the drug to circulate in the body and consequently maintain a consistent attack on the virus. It also means that, whereas standard interferon needs to be taken 3 times a week, pegylated interferon only has to be injected once a week.

2 drug companies manufacture pegylated interferon. Roche Products Ltd make Pegasys (interferon alpha 2A) and Schering-Plough Ltd make ViraferonPeg/PegIntron (interferon alpha 2B). They are similar, although not identical. More details can be found on their websites -see links list top right of page - but before checking them out, you should be aware of 2 things:

• WARNING 1: These websites are intended for a US audience only. In the UK, it is against the law for pharmaceutical companies to promote their products to the general public
• WARNING 2: However they look, these two sites are basically promoting the use of the companies products.

Ribavirin is a synthetic antiviral nucleoside analogue that works very successfully with interferon but not on its own. It was originally developed as an antiviral agent for diseases that cause respiratory problems (it has recently been tried as a treatment for SARS). Its efficacy when used with interferon was first noted in 1990 and since 1998 it has been incorporated into standard treatment for hepatitis C. Ribavirin inhibits viral growth, has anti-viral properties and interrupts the way hepatitis C absorbs genetic material when it replicates.

In the majority of cases ribavirin is used alongside interferon for the treatment of hepatitis C. Ribavirin is ineffective against hepatitis C on its own. Ribavirin comes in 200mg pill or capsule form and is taken orally, twice daily, with dose dependent on patient weight and genotype.

The same 2 drug companies manufacture ribavirin. Roche Products Ltd make Copegus and Schering-Plough Ltd make Rebetol. They are essentially identical. More details can be found on their websites listed above.