How carbamazepine works
As an antiepileptic drug, carbamazepine reduces the hyperexcitability of nerve cells by blocking certain ion channels in the cell membranes. This reduces the risk of an epileptic seizure.
In diseases of the nervous system, this controlled balance can be disturbed. For example, excitation may be increased or inhibition may be reduced due to a genetic predisposition or also due to injuries to the brain. The consequence: The nervous system of the brain is overexcitable – epileptic seizures may occur.
Absorption, degradation and excretion
Carbamazepine is absorbed relatively slowly but completely from the intestine into the blood. The effect occurs after four to 16 hours. This is followed by breakdown in the liver and excretion via the kidney (with urine) and intestine (with stool). After about 16 to 24 hours, half of the absorbed carbamazepine dose has left the body.
When is carbamazepine used?
The uses (indications) of carbamazepine are:
- Nerve damage in diabetes (diabetic neuropathy)
- Trigeminal neuralgia (severe, unilateral facial pain)
- Genuine glossopharyngeal neuralgia (severe pain attacks in the innervation area of the IXth and Xth cranial nerves)
- Non-epileptic seizures in multiple sclerosis
- Seizure prevention in alcohol withdrawal syndrome
- Prevention of manic-depressive episodes in bipolar disorder when lithium is insufficiently effective
How carbamazepine is used
The dosage is determined individually for each patient. As a rule, one starts with 200 milligrams daily. Subsequently, the dose can be slowly increased up to 1200 milligrams. Children, adolescents, elderly patients, patients with cardiovascular diseases and those with kidney or liver dysfunction receive a lower dose.
Patients should undergo genetic testing prior to carbamazepine treatment, as there is ample evidence that certain side effects are more common with certain genetic alterations. If these have been ruled out beforehand, the risk of some side effects is significantly lower.
What are the side effects of carbamazepine?
Occasionally, in less than one percent of those treated, carbamazepine causes involuntary movements, kidney or heart dysfunction, headache, and confusion. Even less commonly, visual disturbances and speech disorders develop.
What should be considered when taking carbamazepine?
Contraindications
Carbamazepine should not be taken by:
- hypersensitivity to the active substance or to any of the other ingredients of the drug
- Bone marrow damage
- certain blood picture disorder (acute intermittent porphyria)
- concomitant use of voriconazole (for fungal infections) or MAO inhibitors (for Parkinson’s disease or depression)
Carbamazepine should be used only after a strict risk-benefit assessment if blood formation disorders, impaired sodium metabolism, or cardiac, renal, or hepatic dysfunction are present.
Drug interactions
Do, carbamazepine may decrease the effects of the following medications, among others:
- other antiepileptic drugs
- benzodiazepines (for sleep disorders)
- tetracyclines (antibiotics)
- indinavir (for HIV infection)
- blood thinners (like warfarin, phenprocoumon)
- theophylline (for respiratory diseases)
- Digoxin (for heart dysfunction)
- thyroid hormones (L-thyroxine)
Conversely, some medications decrease the effect of carbamazepine. These include, for example:
- Theophylline
Effects and side effects of carbamazepine are increased by the following substances, for example:
- certain antibiotics (erythromycin, clarithromycin)
- isoniazid (in tuberculosis)
- verapamil, diltiazem (for cardiac arrhythmias)
- Cimetidine (for heartburn, etc.)
Driving and operating machinery
Carbamazepine may cause side effects such as dizziness, lightheadedness, and fatigue. Therefore, experts advise against actively participating in road traffic or operating heavy machinery at the beginning of therapy. This is especially true in combination with alcohol, as carbamazepine decreases alcohol tolerance.
Age restrictions
Pregnancy and breastfeeding
Carbamazepine may harm the unborn child, so pregnant women with epilepsy should be switched to another antiepileptic drug (e.g., lamotrigine) if possible. If a safe switch is not possible, carbamazepine dosing during pregnancy should be as low as possible and the drug should be taken as monotherapy (not in combination with other antiepileptic drugs).
How to obtain medicines containing carbamazepine
Carbamazepine is subject to prescription in Germany, Austria and Switzerland. It can therefore only be purchased from a pharmacy on presentation of a doctor’s prescription.
