Epilepsy is a disorder that is marked by the occasional, unpredictable occurrence of seizures. However, seizures may occur as a symptom of most any brain injury or lesion. Seizures involve a temporary change of behavior due to disordered and rhythmic electrical signaling of neurons. Drugs that are used to control seizures are called “anticonvulsants” or less frequently, “antiepileptics”.
General mechanisms of anticonvulsants
Some anticonvulsants cause allergic reactions. A physician should be contacted if a rash develops as this may indicate an allergy. The occurrence of a fever, sore throat, oral ulcers or easy bruising should also be reported as this could indicate an effect on important blood cells. Many anticonvulsants can affect a developing embryo so patients should notify their physician if they intend to become pregnant prior to taking an anticonvulsant. Women using oral contraceptive (birth control pills) should also discuss this with their physician because some anticonvulsants reduce levels of estrogen and progestin and therefore make oral contraceptives less effective.
People differ in their ability to eliminate drugs. With many of the anticonvulsants, blood tests are routinely performed to determine if the drug is present at the correct level to produce the desired effect and to assure that the drug is not building up too much to cause toxic effects. Sometimes feeling excessively tired, staggering or slurring of speech can indicate that levels of the drug are too high. A person taking anticonvulsants should not abruptly stop taking the medication without medical advice because this can lead to increased seizure frequency.
Most of the anticonvulsant drugs are involved in many drug interactions. A physician or pharmacist should be consulted before adding any prescription or OTC products while taking these medications.
Commonly used anticonvulsants
Approximately 20% of people receiving long-term phenytoin develop an overgrowth of gum tissue. This may be minimized by good oral hygiene (regular brushing, flossing and gum massage). Other common side effects include decreased coordination, abnormal eye movements (nystagmus), and confusion.
Infrequently abnormal body hair growth or a folic acid deficiency occurs. Elevated blood sugar levels may occur in diabetics. Due to an effect on vitamin D metabolism a small percentage of people develop softening of the bones. Phenytoin may be used in treating excessively prolonged seizures that are sometimes life-threatening. Serious side effects of phenytoin can involve the skin, bone marrow and liver. At high doses impaired consciousness and irregular heart rhythms can occur. Skin rashes should be reported to a physician.
There are many drug interactions with phenytoin. It is metabolized (and inactivated) by enzymes in the liver that metabolize many other drugs. These drugs compete for the enzymes that inactivate them, and the drug that escapes inactivation to a greater extent than normal may accumulate to toxic levels. This type of interaction occurs between cimetidine (commonly used for acid reflux or ulcer type pain) and phenytoin, and can result in phenytoin toxicity. Phenytoin can increase the amount of certain drug-metabolizing enzyme in the liver, possibly diminishing the effect of the other drug. This is thought to be the mechanism by which phenytoin decreases the effectiveness of oral contraceptives. There are other ways by which drug interactions occur.
Phenytoin has other uses including treatment of pain associated with neuralgias, abnormal heart rhythms (rarely), and topically to speed wound healing.
Phenobarbital (many manufacturers)
There are many drug interactions with phenobarbital. This frequently results from the fact that it causes an increase in the amount of liver enzymes that destroys other drugs. For example, by increasing the metabolism of estrogens and progestins, phenobarbital decreases the effectiveness of oral contraceptives.
The most common side effects include drowsiness, dizziness, unsteadiness, blurred vision, GI upset, and water retention. Rarely, carbamazepine causes serious blood problems, liver toxicity, pancreatitis or skin reactions. Fever, black tarry stools, difficulty breathing, sore throat, rash, sores in the mouth, easy bruising, and yellowing of the skin or whites of the eyes should be reported to a physician. Blood tests are routinely performed while on carbamazepine. There are many drug interactions with carbamazepine, including its tendency to decrease the effectiveness of oral contraceptives.
Carbamazepine is used to treat several other conditions including the pain associated with trigeminal neuralgia and other neuralgias, and some psychiatric disorders.
Common side effects include dizziness, fatigue, GI upset, abnormal vision, unsteadiness and tremor. Less frequently it causes low levels of sodium in the blood.
The most common side effects are GI upset, drowsiness, dizziness, headache and fatigue. Infrequently severe skin reactions or blood disorders occur.
Valproic acid (Depakene®); divalproex sodium (Depekote®)
The most common side effects of valproic acid include GI upset, sedation, and weakness. It can also cause bruising, rashes, emotional changes, hair loss and unsteadiness. Less frequently it affects the liver and rarely causes severe liver damage. Periodic blood tests are performed to monitor for liver damage.
The most common side effects of gabapentin include fatigue, dizziness and unsteadiness. These often resolve after several weeks of continuous use. Generally, gabapentin is well tolerated.
Although it has not been approved by the FDA for other uses, gabapentin has also been reported to be effective in the prevention of migraines, and in the treatment of muscle cramps, multiple sclerosis, neuropathic pain, cancer pain, nerve pain associated with diabetes, and some psychiatric disorders.