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Side effects and interactions of AEDs

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Side effects and interactions

Side effects are symptoms caused by medical treatment. They are sometimes called ‘adverse effects’ and are often unwanted or unpleasant. For some people side effects can be positive. For example, side effects that lower your appetite if you are overweight, or that cause sleepiness if you find it hard to sleep.

Do AEDs have side effects?

As with all medications, AEDs can cause side effects and possible side effects vary from one AED to another. Whether you will have side effects or not depends on how you react to the drug (as people can respond differently to the same drug). How important side effects are depends on how important you feel they are to you.

Information about side effects is included in the patient information leaflet (PIL) that comes with the packaging for each medication. The list of side effects can be long and offputting. But listed side effects are only possible effects: they do not always happen. They are often listed by how frequently they occur such as ‘common’ and ‘rare’. These terms are the same for all drugs and they show how likely it is that a side effect will happen (how many people will have it). Knowing what these terms mean may help to put side effects into perspective, and help you to make decisions about taking medication or not.

  • Very common means that at least 1 in 10 people will get it.
  • Common means that 1 in 100 to 1 in 10 people will get it.
  • Occasional means that 1 in 1,000 to 1 in 100 people will get it.
  • Rare means that less than 1 in 1,000 people will get it.
  • Very rare means that less than 1 in 10,000 people will get it.
  • Extremely rare means that less than 1 in 100,000 people will get it.

The possible side effects of AEDs may affect the choice of AED. For example, a drug that may cause extreme sleepiness might be avoided for a student who needs to be alert in class, or a drug that causes weight gain might be avoided for someone who is overweight. There are also particular issues around AEDs for women and girls who are or may become pregnant.

Types of side effects

  • Allergic reactions are rare and usually happen very quickly after starting an AED. An itchy skin rash is often the first sign of an allergic reaction. If you have an allergic reaction it is important that you speak to your specialist, a GP, or pharmacist as soon as possible about what to do. Allergic reactions can be very serious.
  • Dose-related side effects happen when the dose of a drug is too high, and usually go away if the dose is reduced. This is why medication is usually started at a low dose and increased slowly. 
  • ‘Idiosyncratic’ side effects are unique to you (no one else has them).
  • Long-term (or ‘chronic’) side effects happen when a drug is taken for a long time, usually many years.

Side effects can be difficult to recognise in babies, children, and people with learning disabilities as they may not be able to say how they are feeling. If your child is taking AEDs and feels unwell you might notice a change in their behaviour.

If you have a side effect which isn’t listed in the PIL, you can report this to the Medicines and Healthcare products Regulatory Agency (MHRA) – the agency responsible for the safety of medicines in the UK. They run a ‘Yellow Card’ scheme to report side effects which are not listed in the PIL. You can get a Yellow Card by:

  • asking your GP, pharmacist, hospital or NHS drop-in centre; or
  • calling the Yellow Card hotline on 0800 731 6789

It is important to report side effects to the MHRA so that they are aware of those which need to be added to the medication’s PIL.

Although many people are able to take AEDs without problems, for some, taking AEDs can be about balancing the seizure control the drug gives with any side effects it causes. Some people may ‘put up with’ side effects if the medication controls their seizures, but if the medication doesn’t control their seizures well, they may feel it is not worth putting up with the side effects. If you are having side effects that are causing you concern you can talk to your specialist, ESN or GP.

Visit emc for more about side effects.

What are drug interactions?

Some drugs can affect and be affected by other drugs. This is called a ‘drug interaction’. When two drugs interact, how one or both drugs work will be affected. Interactions can result in one or both drugs:

  • working better (being more effective); or
  • working less well, for example, if one prevents the other from working or speeds up how quickly it is eliminated (got rid of) from the body, so it has less time to work.

Drug interactions can happen between different AEDs, and between AEDs and other types of drugs including non-prescription (or ‘over the counter’) medications including complementary therapies and herbal remedies. For this reason, it is helpful to say if you are taking other drugs before starting AEDs, or that you are taking AEDs before starting any other drugs. Usually, there is no interaction between AEDs and frequently used pain relief such as those containing paracetamol or ibuprofen.

AEDs and alcohol

Alcohol can affect how well AEDs work and can also trigger (bring on) seizures for some people (particularly during a hangover). This depends on the AED, how much the person drinks and how they react to alcohol. Drinking alcohol when taking AEDs is a personal choice and the PIL or your specialist will be able to tell you more about drinking alcohol with that medication.

When should I take my AEDs?

AEDs work best when they are taken regularly and at about the same time every day. For most AEDs it does not matter when in the day you take them – morning or evening – only that you try to stick to the same time every day. If you take them more than once a day it is useful to try to take them evenly spaced out (for example, at 8am and 8pm).

It is important to take AEDs regularly because this helps to keep the levels in your body 'topped up' to stop seizures from happening. 

If you are unsure about when to take your AEDs you could talk to your specialist or pharmacist. The aim of taking AEDs is to make your treatment as simple and convenient as possible so that it fits into your daily routine.

How long will I have to take AEDs for?

How long you need to take AEDs depends on your epilepsy, your seizures and how you respond to the AEDs. Most people will take AEDs for at least several years and sometimes for life.

  • For some people, seizures stop or go away of their own accord (called spontaneous remission). In this case, they might come off their medication with help from their neurologist.
  • Some children have an epilepsy syndrome where their seizures stop at a particular age and so they may stop their AEDs.
  • If someone’s epilepsy does not respond to AEDs they might try other types of treatment as well as their AEDs.
  • People who continue to have a tendency to have seizures may always take AEDs. If they stop taking the AEDs the seizures will come back.

Are all AEDs the same?

Most AEDs have two names: a generic name (for example carbamazepine) and a brand or trade name given by the manufacturer (for example Tegretol). The generic name refers to the active ingredient in the drug (which works to control or treat the condition it is taken for).

Some AEDs have more than one generic form, each of which has the same active ingredient, and each can be given its own name. For some AEDs different forms may use different ingredients, such as binding or colouring agents, which can affect how they are absorbed and used in the body. Swapping between different forms of AED could affect seizure control or cause side effects. For this reason it is often recommended that, once you have found a form of AED to control your seizures, you take the same form of this AED all the time (with every prescription) whether it is generic or branded. This is called ‘consistency of supply’.

If a prescription only has the generic name of the drug, a pharmacist can give any form of that drug with that generic name. However, if the prescription has the brand name of the drug the pharmacist must give that brand of AED.

It might be a good idea to keep a note of the generic and brand name (if it has one) for any medication that you take. This might make it easier to recognise if you have been given a different form of medication. It is often a good idea to check what you have been given before you leave the pharmacy so that, if you have any questions about what you have been given, you can talk to the pharmacist. If you have been given a different form, the pharmacist might be able to change this for you.

You may like to take pictures of your medication so that you can show the pharmacist what you normally take.

Some drugs are made abroad and brought into the UK. Other drugs are made in the UK, exported and brought back to the UK. These are called ‘parallel imports’. They are sometimes labelled in a different language or have different packaging from usual. If you are concerned about your medication, you can ask your doctor to write ‘no parallel imports’ on your prescription. Although pharmacists don’t have to follow this, many will try to ensure that you are happy with your medication.

It may be helpful to get your prescriptions from the same pharmacy each time as most pharmacists keep patient medication records and can help you with questions about prescriptions.

Will AEDs affect learning or behaviour?

The aim of medication is to stop seizures without side effects or impact on behaviour. However, some children may have side effects, although these may go away after a few weeks. If their seizures are not well controlled the seizures themselves could affect the child’s behaviour. Some changes in behaviour could be due to other things, such as:

  • where in the brain the seizures happen, what happens during the seizure and how often they happen;
  • how the child feels about their epilepsy and how it affects them; or
  • how other people react to their epilepsy.

However, some changes in behaviour are a normal part of growing up and may not be related to their epilepsy. If you are concerned about whether AEDs are affecting your child you could discuss this with their paediatrician.

Many children with epilepsy find that their epilepsy and medication does not impact on their learning. However, for other children it might, for example, due to seizures disrupting their lessons or medication affecting their concentration. Problems with learning could also be due to the cause of the epilepsy or because they are having seizures. If you are concerned about this you can talk to their paediatrician.

Are there any special issues for girls and women with epilepsy?

Some AEDs can affect periods and contraception and some types of contraception are less effective for girls and women taking particular AEDs. This depends on the individual, which AEDs they take and the type of contraception they use.

Some girls and women have catamenial epilepsy – where their seizures happen at a particular time during their menstrual cycle. They may be prescribed an extra AED,  alongside their regular AEDs, to take when seizures are likely to happen.

Taking AEDs while pregnant may affect a developing baby. However, these risks need to be carefully considered for each person and balanced against the possibility of seizures happening during pregnancy which may also affect a developing baby or the safety of the mother.

Research has shown that sodium valproate (including Epilim, Episenta, Epival and Convulex) has greater risks in pregnancy than other AEDs. Therefore it should not be prescribed to girls and women who are pregnant, or who may become pregnant in the future, unless other AEDs are not effective or cause unbearable side effects.

If you are thinking of starting a family, it is essential that you talk to your neurologist to talk about planning your epilepsy treatment for pregnancy and when your baby arrives, You may have questions about the type of medication you take, the dose, how being pregnant could affect your seizures, and how seizures could affect your unborn baby. 

Visit MHRA for guidance on sodium valproate.

Free prescriptions

If you take AEDs for your epilepsy you are entitled to free prescriptions for your AEDs and any other prescribed medication you take. To apply for free prescriptions in England you need to fill in a FP92A form (from your GP surgery or pharmacy). In Scotland, Wales and Northern Ireland all prescriptions are free for everyone.

You can use the Yellow Card Scheme (opens in new window) for reporting medication side effects.

Information produced: September 2018