The introduction of phenytoin in 1938 ushered in a new era in the treatment of seizures. Phenytoin, sold under the brand name Dilantin, was the first drug that prevented seizures without also causing sedation. It is used to reduce grand mal and complex partial seizures.
Mechanism of Action
A combination of factors make Dilantin effective in preventing seizures. Dilantin reduces the flow of sodium and calcium ions into the neurons, which makes the nervous system less excitable. The drug also increases the level of the neurotransmitter GABA.
Sodium Ions in the Nervous System
The nerve cells rely on the actions of ions to transmit signals. Ions are atoms with a slight electrical charge. These ions cannot penetrate cell membranes, so they must be carried into cells through special channels. When the influx of ions has built up the necessary electrical charge, the nerve cell fires. This sets off adjoining nerve cells to transmit signals throughout the nervous systems. The nerve cell must go through a recovery phase before it can fire again.
Dilantin blocks these sodium channels and increases the time the nerve cell needs to recover. This suppresses seizure-causing electrical activity in the central nervous system.
Neurotransmitters
Dilantin also decreases the ability of calcium ions to inter into cells. The flow of calcium ions into cells stimulates the release of some hormones and neurotransmitters from the cells. Dilantin suppresses the release of the neurotransmitter glutamate and stimulates the release of the neurotransmitter GABA.
GABA is the abbreviation of gamma-Aminobutyric acid. GABA transmits signals from nerve cells to other cells in the body. Neurotransmitters are stored in the nerve endings and released across the gaps, or synapses, between nerve cells. GABA suppresses the central nervous system and makes it less excitable. Drugs that increase GABA levels tend to cause relaxation and drowsiness.
Dilantin reduces the amount of the neurotransmitter glutamate in the central nervous system. Glutamate stimulates the nervous system and makes it more excitable.
Dosage
Dilantin can be toxic at higher doses, so physicians usually run blood tests to check the level of Dilantin in the system. Dosage increases must be done slowly, since small increases can sometimes cause sudden spikes in Dilantin blood levels. Double vision, blurred vision and trouble with balance are often the first signs that Dilantin levels are too high. Since stopping Dilantin suddenly can trigger serious seizures, do not adjust your Dilantin dose unless you are under the direct supervision of a doctor.
References
- "Basic and Clinical Pharmacology;" Bertram Katzung; 2007
