Avonex

Generic Name: Interferon beta-1a
Product Name: Avonex

Indication

Avonex belongs to a class of medications called interferons. It is used to treat patients with the relapsing and remitting type of multiple sclerosis (MS). MS is a chronic and disabling disease of the central nervous system (CNS) thought to be caused by the body’s immune system attacking cells of the brain and spinal cord and leading to demyelination (removal of the electrical conducting layer of nerve cells). It can have various affects on vision, sensation, speech, mood and muscular strength. If left untreated the disease can lead to severe impairments in mobility. Avonex is used to treat the relapsing form of MS where patients experience separated episodes of neurological symptoms caused by lesions at variable locations within the CNS. In between attacks, the condition completely resolves and patients have no symptoms. If you have experienced more than two attacks of symptoms in the last two years you will be considered suitable for treatment with Avonex. Avonex thus reduces the frequency and severity of attacks and delays the overall progression of disability. Note that Avonex is not suitable for progressive types of MS so should be discontinued under the advice of your doctor in these circumstances. Sometimes Avonex will be prescribed following a single episode of neurological symptoms secondary to demyelination. This is done if you are considered at high risk of MS and following identification of lesions on MRI.

Action

The active component of Avonex is a drug called Interferon beta-1a. This is synthesized form of a naturally occurring compound within the body. The interferon family is important in regulating the body’s immune response to viruses, bugs and other noxious stimuli. When administered in patients with multiple sclerosis, Avonex is thought to thought to regulate the body’s immune response to prevent it from attacking its own nerve cells. The drug does this by binding to specific receptors and changing the amounts of certain substances produced, although the precise mechanism of action is not entirely understood.

Dose advice

Avonex is intended for injection into muscle. It is currently available as two forms:

• Powder (white to off-white) separate to the solvent (sterile water)- This comes with a pre-filled solvent syringe, reconstitution device and needle. The powder needs to be carefully mixed (avoid shaking) into the solvent according to the instructions, ensuring there is no particulate matter. The final injection is 1ml.
• Solution (0.5ml)- This comes as pre-filled syringes that just need to have the needle attached for injection.

Both types of Avonex contain the same dose of interferon beta-1a which is 6×10⁶ IU or equivalent to 30 micrograms. Packets of four sets are available. The usual dose is 30 micrograms (i.e. one injection) once per week. You (or your carer) can be taught how to self inject Avonex by an appropriate medical professional. They will supervise your first dose and evaluate your technique prior to you self-injecting at home. You may also take paracetamol prior to your dose and over the next 24 hours to reduce the likelihood of flu-like side effects. The benefits of Avonex occur with long-term use so don’t expect immediate improvement in your condition. You should always take Avonex as prescribed by your doctor and should not cease taking the medication suddenly. Over time however, your body can develop antibodies against interferon beta-1a which reduce the effectiveness of the drug. In this case your doctor will discuss the risks and benefits of continuing treatment in your particular caseDuring your treatment you will require regular monitoring of blood cell counts, platelet counts and liver function tests as Avonex has been shown to disrupt these parameters in some patients. These tests allow your doctor to monitor your progress and avoid unnecessary side effects. In addition you should be careful drinking alcohol as there is a theoretical risk that this may increase the risk of liver damage. Before taking Avonex you should tell your doctor:

• If you are pregnant or intend on becoming pregnant- Avonex should not be used in these circumstances due to the risk of miscarriage. All women of child-bearing age should take birth control during their treatment.
• If you have any other medical conditions- In particular tell your doctor if you have depression, seizure disorders, heart, lung or kidney disease, or bone marrow suppression as these can increase your risk of certain adverse effects. Avonex should not be taken by patients with severe depression or suicidal thoughts as it may exacerbate these conditions. If you develop any symptoms of severe sadness, worthlessness or hopelessness during your treatment seek medical help immediately.
• If you are allergic to any medications, foods or dyes- Avonex should not be used in patients allergic to this type of medication (interferon beta), albumin or any of the other components. If you have an allergy to natural rubber you should use the powder form of medication. Note the human albumin in the powder form causes a small increase in the risk of infection.
• Any other medications you are taking (including those bought from supermarkets or the chemist)- Avonex can react with some medicines used to treat epilepsy and depression and drugs affecting the bone marrow.
• Avonex is not recommended for use in patients under 18 years of age due to the lack of experience in his age group.

Schedule

S4 (prescription required). Refer to the PBS for authority indications.

Common side effects

Avonex helps most people with MS but like all medications may have unwanted side effects in some people. The most commonly reported side effects (occurring in greater than 1% of patients) include:

• Flu-like symptoms (mainly muscle aches, fever and chills). These symptoms are usually worst when you are just starting the drug. The symptoms can be reduced by taking paracetamol before and for one day after the injection.
• Headache.
• Fatigue.
• Nausea.
• Vomiting.
• Anorexia (reduced appetite).
• Abdominal pain.
• Insomnia and sleep difficulties.
• Excess sweating and rash.
• Muscle ache and spasm.
• Depression.
• Elevation of liver enzymes.
• Haematologic abnormalities such as changes in blood counts.

In most patients however, Avonex is well tolerated and side-effects are only minor. Most of the side-effects listed above will be self-limiting and they often decrease over time as the body gets used to the medication. If you are having any side-effects that are worrying you or creating inconvenience discuss them with your doctor.

Uncommon side effects

Like all medications, Avonex has the potential to cause serious side-effects. Fortunately only a very small number of patients (less than 0.1%) taking Avonex will develop the more nasty and serious side-effects which may warrant changing medication or in some cases pose significant risks to the patient’s health and well-being. In most circumstances these side-effects can be treated without any long-term complications. Some of the more serious side-effects of Avonex include:

• Allergic reactions- If you develop difficulty breathing, rashes, swelling of the face, itchy skin or wheezing seek medical advice immediately.
• Infection at the injection site which will appear as a red, swollen and painful area that may have a discharge.
• Cardiovascular disorders- Palpitations, heart failure and cardiomyopathies are rare side effects of interferon beta drugs. If you notice breathlessness, persistent cough, swelling in hands or feet, or palpitations (sensation of an irregular heartbeat) see your doctor.
• Severe depression with thoughts of suicide.
• Seizures, fits, convulsions or fainting.
• Liver damage- Yellowing of the skin or eyes (jaundice) is a sign of hepatic dysfunction.
• Severe reductions in blood counts.

The above serious side effects usually require medical treatment. Note however, that these lists of side effects ae not necessarily exhaustive. Every patient is different and you may find that Avonex causes different symptoms for you which should be discussed with your doctor. Do not be alarmed by these lists most patients taking Avonex do not experience any side-effects at all. It is important for you to weigh up the risks and benefits of the drug (with the advice of your doctor) in your individual case to decide if this drug is suited for you.

References

1. Australian Medicines Handbook- 16.7 Interferon Beta. AMH Pty Ltd. 2006.
2. Avonex (R)- Consumer Medicine Information, Biogen Idec Australia Pty Ltd 2006. Available from: [PDF File]
3. MIMS online- Prescribing Information. Avonex. MIMS Australia Pty Ltd 2003.

For further information talk to your doctor.