Electrical signals are sent from the cell body along the axon to the synapse, these electrical signals being the result of ion sodium, potassium, calcium currents across channels in the nerve cell membrane. Chemical signals neurotransmitters pass across synapses between neurons. Neurotransmitters cross the synaptic gap between neurons and fix to receptor points of the adjoining neuron. Some neurotransmitters function to excite the joining neuron eg. Other neurotransmitters function to inhibit the joining neuron eg.
GABA and inhibit electrical signals passing down that neuron. It is by these electrical and chemical pathways that the millions of neurons within the brain communicate and function normally. Seizures occur when there is an imbalance within these excitatory and inhibitory circuits in the brain, either throughout the brain generalised epilepsy or in a localised part of the brain focal epilepsy , such that neurons "fire off" in an abnormal fashion.
Antiepileptic medications work in different ways to prevent seizures, either by decreasing excitation or enhancing inhibition. Specifically, they act by either:. As the specific mechanisms that cause epilepsy are mostly unknown, drugs with specific mechanisms of action directed at the underlying "epileptic processes" have not yet been developed. An antiepileptic medication is swallowed by mouth and passes directly to the stomach. Once in the stomach the medication is absorbed into the blood stream where it is then circulated to the brain, via the liver, and acts on the nerve cells.
As the drug is circulating in the blood, it is gradually removed by either the liver breaking it down metabolism or the kidneys filtering it out excretion. Some drug metabolites are active and produce either beneficial antiepileptic effects or adverse side effects. Most commonly prescribed antiepileptic medications are removed from the blood at a rate that allows twice daily dosing to maintain adequate blood levels.
Some drugs are removed more quickly than others and have to be taken 3 or 4 times throughout the day, whilst others are removed slowly and can be taken once each day. For some medications, children need to have blood tests to determine the level in the bloodstream eg. These blood levels are generally measured before a dose is due. Not all antiepileptic medications need to be monitored with drug levels, as there is not a good correlation between drug level and effect.
The dose of medication prescribed is determined by the child's age and weight. Young children and adolescents have greater rates of drug clearance and are often prescribed doses per kilogram of body weight greater than an adult would receive.
In an emergency situation, such as status epilepticus, some antiepileptic drugs can be given directly into the blood stream, into the rectum, nose or buccal to act very quickly to control seizures. The choice of medication and how each is prescribed is a specialist area of paediatrics and child neurology. Prescription of antiepileptic medication is only done by a doctor with knowledge of antiepileptic medication and epilepsy in children.
General principles that doctors follow when prescribing antiepileptic medications in children include:. All medications have the possibility of causing side effects. There are three main types of antiepileptic medication side effects. Please refer to the specific drug information provided with your medication for a more detailed list of side effects. The tablets break down, releasing the medication which can then pass through the wall of the gut into the bloodstream absorption , and be distributed around the body.
The quicker the medicine gets into the bloodstream the quicker it can get to work. How well and quickly the drugs get to their site of action depends on how well the part of the body is supplied with blood, and how easily the drug gets from the blood stream into the part of the body.
Although the brain has a good supply of blood, there is a barrier between the blood and the brain that helps protect the brain from infections and toxic chemicals.
This means that drugs do not pass easily into the brain. Once drugs have played their active role, they start to break down metabolise so that they can be excreted from the body passed out through the digestive tract, like food and drink, or in the urine. How long before AEDs start to be metabolised varies from one to another and is referred to as their half-life.
To be excreted in the urine, AEDs have to be broken down so that they can dissolve in water, and then the kidneys can get rid of them. Some AEDs become inactive when they are metabolised. Most AEDs are metabolised in the liver hepatic metabolism where they are changed into water-soluble metabolites with the help of different enzymes. Some AEDs — gabapentin, vigabatrin, levetiracetam and pregabalin, are not metabolised, not affected by hepatic enzymes, and they are excreted in the same form in the urine.
AEDs make the brain less likely to have seizures by altering and reducing the excessive electrical activity or excitability of the neurones that normally cause a seizure. Different AEDs work in different ways and have different effects on the brain.
How exactly some AEDs work is still not fully understood. There are several different ways in which AEDs stop seizures from happening, by working on particular targets in the brain. AEDs may affect the neurotransmitters responsible for sending messages, or attach themselves to the surface of neurones and alter the activity of the cell by changing how ions chemicals found in the body that have an electrical charge , flow into and out of the neurones.
Sodium channels are the parts of the neurone that affect how electrical signals or messages are passed along the length of a neurone. This is because they change the amount of ions inside and outside the cell, which then changes the electrical charge of the cell. Some AEDs such as phenytoin, lamotrigine and carbamazepine work by affecting the sodium channels of neurones. AEDs that bind or attach themselves to the sodium channels affect how ions flow through the channels, and stop the channel becoming activated or creating an action potential.
Some side effects may be life-threatening. Talk to your healthcare provider about possible side effects with your medication. The decision when to start medication can be difficult. A first seizure may not mean that you will have a second seizure and a second seizure may not occur for years later. The decision to start medication should be made by thinking about the benefits and risks of starting, or not starting, the medicine.
A common option is to wait and see after a first seizure. If you have a second seizure within a few months, more are likely, so it may be a good idea to think about starting medication. Your health professional can discuss the best medication for you. It may take some time to find the AED that works best for you.
In most cases, only one AED is needed to prevent seizures, but some people may need two or more medicines. It is also important for you to think about the benefits and risks of taking, or not taking, AEDs. This may depend on how your seizures affect you and how often they happen. The following table sets out what you might want to think about to help you decide whether to take AEDs or not.
Therefore, if you are troubled with a side-effect, a change of medication may resolve the problem. When you start a medicine, ask your doctor about any problems which may arise for your particular medicine. Two groups of problems may be mentioned:. Note : you should not stop taking a medicine suddenly. If you notice a side-effect, you should ask your doctor for advice. It is important to take your medicine as prescribed. Try to get into a daily routine.
Forgetting an occasional dose is not a problem for some people; however, for others this would lead to breakthrough seizures. One of the reasons why seizures recur is due to medication not having been taken properly. A pharmacist can be a good source of advice if you have any queries about medication. You will need an exemption certificate. Ask your pharmacist for details. Some medicines taken for other conditions may interfere with medication for epilepsy. If you are prescribed or buy another medicine, always remind your doctor or pharmacist that you take medication for epilepsy.
Even preparations such as indigestion medicines may interact with your epilepsy medication, which may increase your chance of having a seizure. Some epilepsy treatments interfere with the contraceptive pill. You may need a higher-dose pill or an alternative method of contraception.
For reliable contraception, it is best to seek advice from a doctor or nurse. They will be able to tell you if your epilepsy treatment affects any methods of contraception. For women with epilepsy, the risk of complications during pregnancy and labour is slightly higher than for women without epilepsy. The small increase in risk is due to the small risk of harm coming to a baby if you have a serious seizure whilst pregnant. There is also a small risk of harm to an unborn baby from anti-epilepsy medicines.
Before becoming pregnant it is important to seek advice from your doctor. Any potential risks can be discussed. For example, to go over your current medication and to see if it should be changed to minimise the risk of harm to a developing baby. One important point is that you should take extra folic acid folate before becoming pregnant and continue it until you are 12 weeks pregnant.
If you have an unplanned pregnancy, you should not stop epilepsy medication, which may risk a seizure occurring. Continue your medication and see a doctor as soon as possible. See the separate leaflet called Epilepsy and Planning Pregnancy for more details. You may wish to consider stopping medication if you have not had any seizures for two or more years.
It is important to discuss this with a doctor. The chance of seizures recurring is higher for some types of epilepsy than others. Overall, if you have not had any seizures for years and you then stop medication:.
There are many different types of epilepsy, some of which are age-dependent but some that will need medication for life. Your epilepsy specialist should be able to offer you more advice about the long-term outlook for your particular type of epilepsy. Your life circumstances may influence the decision about stopping medication. For example, if you have recently regained your driving licence, the risk of losing it again for a year if a seizure occurs may affect your decision.
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