Side Effects of Low Dilantin Levels

Dilantin is the trade name for the anti-seizure medication phenytoin. This medicine is an anti-epileptic and anti-convulsant drug used to reduce the frequency and severity of seizures in acute and chronic cases. Another use for Dilantin is as an anti-arrhythmic medication. Side effects of low (sub-therapeutic) Dilantin levels in individuals with seizure disorders will be the symptoms of those disorders. There are different types of seizures varying in intensity, duration and outward appearance. For cardiac patients, low Dilantin levels can result in arrhythmias. (see Reference 1)

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Generalized Seizures

Low levels of dilantin can cause generalized seizures in patients who are managed and treated with this anti-convulsant medication. Generalized seizures occur when the entire brain is involved. These usually begin as a local or partial seizure and spread across the brain. There is usually a metabolic or hereditary component to these cases. Generalized seizures can be obvious like the prototypical “grand-mal,“ or they can be totally silent like the “petit-mal” seizure. It is important to be sure that the patient doesn’t hurt himself during a seizure and to provide supportive care after the seizure has passed. (see Reference 2)

Partial Seizures

Low dilantin levels can increase the frequencies of partial seizures in certain patients managed with this medication. Partial seizures result when only a part of the brain is affected by the pathological process. Although this usually happens after stroke, infection or trauma, many of the cases have unknown causes. Partial seizures can involve a motor function, like a muscle or group of muscles that have the seizure. They can also involve sensory functions where an individual sees, smells, hears or tastes something that is not really there. Seizures in other parts of the brain can result in dream-like states and loss of consciousness.


Dilantin is also used to treat arrhythmias in patients on digitalis medications. In these patients low dilantin levels can increase the risks and frequencies of heart arrhythmia. Arrhythmia occurs when the normal heartbeat is interrupted or altered in some way. It is a problem because this interferes with the efficient pumping of blood through the body. Arrhythmia can occur for many different reasons, including damage to the heart's conducting system, metabolic disorders, previous heart attacks, other cardiac injuries or for reasons unknown. There are some very severe arrhythmias for which Dilantin is useful to stop the abnormal beating and return the heart to its normal rhythm. (see Reference 3)