Phenytoin is an anticonvulsant.

Phenytoin is a drug that in medicine belongs to the group of anticonvulsants (anticonvulsants). It is mainly used for the treatment of two different clinical pictures: epilepsy and cardiac arrhythmias.


With regard to epilepsy, phenytoin is used both for the treatment of acute seizures and for long-term treatment. However, phenytoin has been prescribed less frequently in the treatment of acute seizures for several years, as newer drugs have fewer side effects and interactions with other drugs.

In cardiology, phenytoin is mainly used when the clinical picture of ventricular tachycardia is present (this is understood to mean too high a heart rate per minute). Ventricular tachycardia usually occurs after poisoning with digitalis, the poison of the thimble.

In its mode of action phenytoin is very similar to lidocaine, a medicine that can induce local anesthesia. Both substances block a sodium channel in the membrane of nerve cells, a structure that is indispensable for the generation and transmission of information (including the information of a pain stimulus) in the nervous system.

Phenytoin is metabolised in the liver and excreted via the kidney.

side effects

In connection with the use of phenytoin, some side effects are known: reported dizziness, nystagmus (uncontrollable spontaneous eye movements), double vision or ataxia (impaired locomotor coordination).

It may also lead to nausea, polyneuropathy (diffuse sensory disturbances due to damage to the nervous system), enlargement of the oral mucosa and hirsutism (increased body hair in women). Also about disorders of blood formation, diseases of the lymph nodes, liver dysfunction and allergic reactions.


With regard to interactions of phenytoin with other drugs, the following distinction can be made:

There are substances that increase the levels of phenytoin in the blood, such as sulfonylureas (commonly used to treat type II diabetics), cimetidine (an antiallergic), antibiotics, tuberculosis drugs and psychotropic drugs, such as benzodiazepines and tricyclic antidepressants (see below) one understands a certain group of mood-lifting medicines). Also for drugs for rheumatism, the anesthetic halothane and disulfiram, the use in the cessation of alcohol, this effect is known.

Substances that lower the drug level of phenytoin include alcohol and other anti-spasmodic drugs such as carbamazepine, phenobarbital, and primidone.

However, even phenytoin itself can reduce other drugs in their effectiveness, if a simultaneous intake takes place. This is known for: contraceptives ("the pill"), antibiotics such as doxycycline, certain antidepressants, anticoagulant drugs and verapamil, which is used to relieve cardiac arrhythmias.

Phenytoin should not be taken in the case of the following diseases: Pregnancy, liver disease, bone marrow disease, heart failure and / or in the case of a so-called sick sinus syndrome (cardiac arrhythmia, which usually develops after damage to the sinus node in the heart),

Phenytoin in pregnancy

Caution should be exercised during pregnancy and lactation with phenytoin. It may only be used after careful consultation with a doctor and a precise risk-benefit assessment. Taking phenytoin may increase the risk of malformations.

The efficacy of certain contraceptives may be limited by phenytoin. The risk of malformations, such as neural tube defects, developmental delays or heart defects can be increased. If the medication is indispensable, treatment with the lowest effective dose will be used to achieve seizure suppression. This is especially important between the 20th and the 40th day of pregnancy. Concomitant use of other anticonvulsant drugs should be avoided, as they increase the risk of malformations.

However, with all the potential side effects, it is strongly discouraged to discontinue phenytoin therapy on its own during pregnancy. This can lead to a rapid reduction in the dose of phenytoin in the blood, which can cause seizures. However, these seizures can have fatal consequences for mother and child. Therefore, monitoring the dose of phenytoin in the mother's blood plasma during pregnancy and during childbirth is very important. After pregnancy, the phenytoin level in the blood increases, so that an adjustment of the dose may be necessary.

In order to avoid bleeding in the unborn child, pregnant women taking phenytoin should take vitamin K in the last few weeks of pregnancy. This is done after consultation with the attending physician. After birth, the newborn should also receive preventive vitamin K to prevent bleeding.

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