Phenytoin is a drug that is classified in medicine as an anticonvulsant. It is mainly used to treat two different clinical pictures: epilepsy and cardiac arrhythmia.
Application
With regard to epilepsy, phenytoin is used both for the treatment of acute seizures and for long-term treatment. However, for some years now, phenytoin has been prescribed less frequently in the treatment of acute seizures because newer preparations 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 an excessive number of beats per minute of the heart chambers).
Ventricular tachycardia is usually caused by poisoning with digitalis, the poison of the foxglove. In its mode of action, phenytoin is very similar to lidocaine, a drug with which local anesthesia can be induced. 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 kidneys.
Side effects
In connection with the intake of Phenytoin some side effects are known: Dizziness, nystagmus (uncontrollable spontaneous eye movements), double vision or ataxia (disturbance of movement coordination) are reported. In addition, there may also be 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 blood formation disorders, lymph node diseases, liver dysfunction and allergic reactions.
Interactions
With regard to interactions of Phenytoin with other drugs, the following distinction can be made: There are substances that increase the level of active ingredients of phenytoin in the blood, such as sulfonylureas (commonly used to treat type II diabetics), cimetidine (an anti-allergic drug), antibiotics, drugs for the treatment of tuberculosis and psychotropic drugs such as benzodiazepines and so-called tricyclic antidepressants (a certain group of mood-lifting drugs). This effect is also known for medicines against rheumatism, the anaesthetic Halothane and Disulfiram, which is used in alcohol weaning. Substances that lower the active ingredient level of phenytoin are alcohol and other antispasmodic drugs such as carbamazepine, phenobarbital and primidone.
However, Phenytoin itself can also reduce the effectiveness of other drugs if taken at the same time. This is known for: Contraceptives (“the pill”), antibiotics such as doxycycline, certain antidepressants, anticoagulants and verapamil, which is used to relieve heart rhythm disturbances. Phenytoin must not be taken in the case of the following conditions: In case of pregnancy, liver diseases, bone marrow diseases, cardiac insufficiency and/or in case of so-called sick sinus syndrome (cardiac arrhythmia, which usually occurs after damage to the sinus node of the heart).
