What are Disease Modifying Drugs?

Unlike symptomatic therapies, disease modifying drugs are drugs which can beneficially slow the long-term course of MS.

They have been shown to reduce the frequency and severity of relapses and slow the development of disability in people with relapsing forms of MS. They do not appear to modify the progressive forms of MS when people are not having relapses. At present none of them is a cure for MS.

There are three types of DMD which are licensed in the UK for the treatment of MS. These are:

• Interferon beta - there are four interferon beta drugs that come in two forms, interferon beta-1a (sold as Avonex® and Rebif®) and interferon beta-1b (sold as Betaferon® and Extavia®. Extavia is a bio-equivalent of Betaferon).
• Glatiramer acetate (sold as Copaxone®)
• Natalizumab (sold as Tysabri®)

How do these drugs work?

The way the disease modifying drugs are thought to work is based on the idea of MS as an autoimmune disease.

There is no complete understanding of how interferon beta, glatiramer acetate and natalizumab work in the human body. However, research in these areas is improving all the time, and the following is a basic guide.

Interferon betas

Interferons are proteins produced naturally by the human body. They help to fight viral infections and play a vital role in the functioning of the immune system.

There are three types of natural interferon: alpha, beta and gamma. Interferon alpha is used in cancer treatments, and is not thought to be of benefit in treating people with MS. Interferon gamma has been tried in MS, and research showed that it could actually induce MS symptoms.

Interferon beta is known to block the action of interferon gamma, and it is thought that interferon beta acts in MS by reducing both inflammation and the body's autoimmune reaction that is responsible for the inflammation and consequent damage to myelin and nerve fibres.

Two different forms of interferon beta molecule are available as drugs for MS, interferon beta 1a and interferon beta1b. The differences are due to the manufacturing processes.

Glatiramer acetate

Glatiramer acetate is completely different from interferon beta. It is a laboratory made drug, made of protein molecules (amino acids) that naturally occur in the human body.

Glatiramer acetate is designed to mimic the effects of the main proteins in myelin. Once injected, the drug is thought to work by connecting to cells in the immune system that can reach the myelin sheath under attack. These cells are thought to dampen down inflammation occurring in the central nervous system (brain, optic nerves and spinal cord), and so reduce damage to myelin and nerve fibres.

Natalizumab

Natalizumab is a newer type of drug known as a selective adhesion-molecule (SAM) inhibitor.

In MS, it is believed that immune cells (white blood cells) pass through the blood-brain barrier into the central nervous system (brain, optic nerves & spinal cord). These cells can cause inflammation and damage nerves and the surrounding myelin sheath. Adhesion molecules on the surface of immune cells play an important role in this process. Natalizumab attaches itself (binds) to a specific adhesion molecule on the immune cell surface known as alpha-4 integrin and it is thought to act by preventing the immune cells from passing into the central nervous system via the blood brain barrier.