Carbamazepine (Carbagen SR)
How does it work?
Carbagen SR tablets contain the active ingredient carbamazepine, which is a medicine that is mainly used to treat epilepsy. It works by stabilising electrical activity in the brain. (NB. Carbamazepine is also available without a brand name, ie as the generic medicine.)
The brain and nerves are made up of many nerve cells that communicate with each other through electrical signals. These signals must be carefully regulated for the brain and nerves to function properly. When abnormally rapid and repetitive electrical signals are released in the brain, the brain becomes over-stimulated and normal function is disturbed. This results in fits or seizures.
Carbamazepine prevents epileptic fits by preventing the excessive electrical activity in the brain. It is thought to achieve this by preventing sodium from entering nerve cells when they begin to fire rapid and repetitive electrical signals. A build up of sodium in the nerve cells is necessary for the electrical signal to build up and be passed on to other nerve cells. As carbamazepine prevents this, it helps stabilise the electrical activity in the brain.
Preventing the build-up of the electrical signal also prevents the release of a neurotransmitter called glutamate from the nerve cells in the brain. Neurotransmitters are chemicals that are stored in nerve cells and are involved in transmitting messages between the nerve cells. Glutamate is a neurotransmitter that acts as a natural 'nerve-exciting' agent. It is released when electrical signals build up in nerve cells and subsequently excites more nerve cells. It is thought to play a key role in causing epileptic seizures. Reducing the release of glutamate from the nerve cells in the brain is another way in which carbamazepine is thought to help stabilise the electrical activity in the brain and prevent epileptic fits.
As carbamazepine stabilises electrical nerve activity, it is also used to treat a condition called trigeminal neuralgia, in which the facial nerves spontaneously send messages of pain to the brain. Carbamazepine prevents the nerve signals being sent inappropriately and relieves the pain of this condition.
Lastly, carbamazepine is used as a mood stabiliser for treating people with the psychiatric illness, bipolar affective disorder. It is licensed for preventing episodes of ill health (abnormally high and low mood) in people with bipolar disorder who have not responded to the older mood stabiliser, lithium. It is particularly useful for people who experience multiple mood swings (rapid cycling). Carbamazepine is also used off-licence by specialists to control episodes of mania in this illness. It is not fully understood how carbamazepine works as a mood stabiliser, but is thought to be to do with the reduction of glutamate activity in the brain.
Carbagen SR tablets are modified release tablets. They are designed to release the carbamazepine slowly and continuously over a few hours to help provide steady blood levels of the medicine. These tablets must not be crushed or chewed, to avoid damaging the modified release action. However, the tablets can be broken in half.
What is it used for?
- Epilepsy. Carbamazepine is used to treat generalised tonic-clonic seizures (grand mal epilepsy) and partial seizures.
- Severe pain in the lips, gums, cheek, chin or eye caused by a disorder of the nerves in the face (trigeminal neuralgia).
- As a mood stabiliser in bipolar affective disorder to help prevent episodes of mania or depression.
- Treatment of acute manic episodes in bipolar affective disorder (unlicensed use).
- This medicine may cause dizziness and drowsiness. You should take care when performing potentially hazardous activites, such as driving or operating machinery, until you know how this medicine affects you and are sure you can perform such activities safely.
- It is recommended that you avoid drinking grapefruit juice while taking this medicine. This is because grapefruit juice can affect the metabolism of carbamazepine and could increase the amount of the medicine in your blood, thus increasing the risk of side effects.
- This medicine may cause skin reactions. You should let your doctor know if you develop a rash, skin peeling, itching, or other unexplained skin reaction while taking this medicine.
- This medicine can sometimes cause a decrease in the normal amounts of blood cells in the blood. For this reason you should consult your doctor immediately if you experience any of the following symptoms, as they may indicate a problem with your blood cells: unexplained bruising or bleeding, purple spots, sore throat, mouth ulcers, high temperature (fever), feeling tired or general illness. Your doctor may want to take a blood test to check your blood cells.
- This medicine may rarely cause liver problems. For this reason you should consult your doctor promptly if you develop any of the following symptoms while taking this medicine, as they may indicate a problem with your liver: unexplained itching, yellowing of the skin or eyes, unusually dark urine, nausea and vomiting, abdominal pains, loss of appetite or flu-like symptoms.
- While taking this medicine your doctor will want you to have regular blood tests to monitor your liver function and the number of blood cells in your blood.
- There may be a small increased risk of suicidal thoughts and behaviour in people taking antiepileptic medicines such as carbamazepine for any condition. For this reason, it is very important to seek medical advice if you, or someone else taking this medicine, experience any changes in mood, distressing thoughts, or feelings about suicide or self-harm at any point while taking this medicine. For more information speak to your doctor or pharmacist.
- Carbamazepine decreases the blood levels of hormonal contraceptives containing oestrogen and/or progesterone, which may make the contraceptive ineffective or result in breakthrough bleeding. Women taking this medicine who require contraception should be prescribed a contraceptive containing at least 50 micrograms of oestrogen, or use non-hormonal methods of contraception, such as condoms. Ask your doctor for further advice.
- If you have epilepsy it is important to take your medication regularly, as directed by your doctor, because missing doses can trigger seizures in some people. If you have trouble remembering to take your medicine you should ask your pharmacist for advice. You may find a pill reminder box helpful.
- You should not suddenly stop taking this medicine unless your doctor tells you otherwise, as suddenly stopping treatment is likely to make your symptoms return. If this medicine is stopped, it should normally be done gradually, under the supervision of your specialist.
- Wherever possible it is recommended that people with epilepsy always receive the same brand of their antiepileptic medicine. This is because different brands of these medicines may differ in the way they are absorbed into the body, which could either reduce the effect of the medicine and increase the risk of seizures, or increase the effect of the medicine and hence increase the risk of side effects. You should make sure you know what brand of carbamazepine you normally take and check with your pharmacist if you are ever dispensed a different brand.
Use with caution in
- Mixed seizures including absence seizures.
- Elderly people.
- History of heart disease.
- History of kidney disease.
- History of liver disease.
- History of psychotic illness.
- Raised pressure in the eye (intraocular pressure), eg glaucoma.
- History of blood disorders that were caused by any other medication.
- History of previous carbamazepine therapy that was interrupted due to side effects or allergy.
Not to be used in
- Problems with the electrical message pathways in the heart (atrioventricular block).
- History of decreased blood cell production by the bone marrow (bone marrow depression).
- Hereditary blood disorders called porphyrias.
- Allergy to tricyclic antidepressants, eg amitriptyline.
- People who have taken a monoamine-oxidase inhibitor antidepressant (MAOI) in the last 14 days.
- Carbagen SR tablets are not recommended for children under five years of age.
This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
Pregnancy and breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
- It is vital that women with epilepsy receive specialist advice before getting pregnant, so they are well informed of potential risks and benefits of continuing antiepileptic treatment. Pregnant women taking antiepileptic medicine have a higher risk of carrying a baby with developmental problems and malformations. However, if a woman with epilepsy stops treatment because she is pregnant, there is a risk of seizures that can harm both mother and baby. It is important that all the risks and benefits of treatment are weighed up. Seek medical advice from your doctor.
- Women who decide to try for a baby while taking carbamazepine should start taking folic acid daily as soon as contraception is stopped, as this may reduce the risk of neural tube defects such as spina bifida in the baby. Ask your doctor for advice on the dose to take - it may be recommended that you take 5mg daily.
- Women who continue to take carbamazepine during a pregnancy should, wherever possible, be prescribed carbamazepine on its own, in the lowest effective dose, to minimise the risk to the baby. Specialist medical advice must be sought.
- This medicine passes into breast milk. The benefits of breastfeeding should be weighed against any possible risks to the infant. Breast-fed infants should be observed for possible adverse reactions of the medicine, such as excessive drowsiness, skin rashes or poor weight gain. Discuss this with your doctor.
- This medication is to be swallowed whole, not chewed.
- This medication may cause drowsiness. If affected do not drive or operate machinery.
- Do not stop taking this medication except on your doctor's advice.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.
- Shaky movements and unsteady walk (ataxia).
- Allergic skin reactions.
- Disturbances of the gut such as diarrhoea, constipation, nausea, vomiting or abdominal pain.
- Double vision.
- Blurred vision.
- Decreased numbers of white blood cells, red blood cells or platelets in the blood.
- Dry mouth.
- Retention of water in the body tissues (fluid retention).
- Weight gain.
- Abnormal involuntary movements (twitching or tics).
- Alteration in results of liver function tests.
- False perceptions of things that are not really there (hallucinations).
- Speech disorders.
- Severe blistering skin reaction affecting the tissues of the eyes, mouth, throat and genitals (Stevens-Johnson Syndrome).
- Liver, kidney or heart disorders.
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
How can this medicine affect other medicines?
Carbamazepine can interact with many medicines and the dose of carbamazepine or the interacting medicine may need to be altered as a result. It is important to tell your doctor what medicines you are taking, including herbal medicines and non-prescription medicines, before you start carbamazepine. Likewise, once you are taking carbamazepine it is important to check with your doctor or pharmacist before you stop taking any existing medicines, or start taking any new medicines, including herbal medicines and those bought without a prescription.
The following medicines may reduce the breakdown of carbamazepine in the body. As this could increase the level of carbamazepine in your blood and may increase the risk of side effects, your doctor may need to decrease your carbamazepine dose if you are prescribed any of these:
- azole antifungals, eg fluconazole, ketoconazole, itraconazole, miconazole
- macrolide antibiotics, eg erythromycin, clarithromycin
- protease inhibitors (HIV), eg ritonavir
The following medicines may increase the breakdown of carbamazepine in the body. As this could decrease the level of carbamazepine in your blood and may make it less effective, your doctor may need to increase your carbamazepine dose if you are prescribed any of these:
- the herbal remedy St John's wort (Hypericum perforatum). This should not be taken by people who are taking carbamazepine.
Sodium valproate and lamotrigine may increase the rate that carbamazepine is converted to another active form in the body. This can result in an increase in carbamazepine side effects.
Carbamazepine may increase the breakdown of the following medicines in the body. As this could decrease the level of these medicines in the blood and may make them less effective, your doctor may need to prescribe a larger than normal dose of these:
- benzodiazepines, eg alprazolam, clonazepam, diazepam, midazolam
- calcium channel blockers, eg felodipine, nimodipine
- corticosteroids, eg dexamethasone, prednisolone
- oestrogens (carbamazepine makes hormonal contraceptives less effective - see the warning section above for more information)
- progestogens (carbamazepine makes hormonal contraceptives less effective - see the warning section above for more information)
- protease inhibitors (for HIV infection), eg indinavir, saquinavir, nelfinavir, lopinavir
- sodium valproate
- thyroid hormones
- tricyclic antidepressants such as imipramine, amitriptyline, nortriptyline, clomipramine
Carbamazepine may raise or lower the blood level of phenytoin.
The manufacturer states that carbamazepine should not be taken in combination with monoamine oxidase inhibitor antidepressants (MAOIs, eg phenelzine, tranylcypromine, isocarboxazid). At least two weeks should pass after stopping an MAOI before starting carbamazepine.
If carbamazepine is taken with diuretics such as furosemide or hydrochlorothiazide there may be an increased chance of a fall in the level of sodium in the blood.
If carbamazepine is taken with lithium or haloperidol there may be an increase in brain and nervous system side effects, eg confusion, drowsiness, weakness, lethargy and tremor.
If carbamazepine is taken with isoniazid or sodium valproate there may be an increased risk of side effects on the liver.
Other medicines containing the same active ingredient
Carbamazepine tablets are also available without a brand name, ie as the generic medicine.