Anticonvulsant Drugs

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Anticonvulsant Drugs



Anticonvulsant drugs are medicines used to prevent or treat convulsions (seizures).


Anticonvulsant drugs are used to control seizures in people with epilepsy. Epilepsy is not a single disease—it is a set of symptoms that may have different causes in different people. The common thread is an imbalance in the brain's electrical activity. This imbalance causes seizures that may affect part or all of the body and may or may not cause a loss of consciousness. Anticonvulsant drugs act on the brain to reduce the frequency and severity of seizures.
Some cases of epilepsy are brought on by head injuries, brain tumors or infections, or metabolic problems such as low blood sugar. But in some people with epilepsy, the cause is not clear.
Anticonvulsant drugs are an important part of the treatment program for epilepsy. Different kinds of drugs may be prescribed for different types of seizures. In addition to taking medicine, patients with epilepsy should get enough rest, avoid stress, and practice good health habits.
Some physicians believe that giving the drugs to children with epilepsy may prevent the condition from getting worse in later life. However, others say the effects are the same, whether treatment is started early or later in life. Determining when treatment begins depends on the physician and his assessment of the patient's symptoms.
Physicians also prescribe certain anticonvulsant drugs for other conditions, including bipolar disorder and migraine headaches.


Anticonvulsant drugs may be divided into several classes. The hydantoins include pheytoin (Dilantin) and mephenytoin (Mesantoin.) Ther succimides include ethosuximide (Zarontin) and methsuccimide (Celontin.) The benzodiazepines, which are better known for their use as tranquilizers and sedatives, include clonazepam (Klonopin), clorazepate (Tranxene) and diazepam (Valium.) There are also a large number of other drugs which are not related to larger groups. These include carbamazepine (Tegretol), valproic acid (Depakote, Depakene) gabapentin (Neurontin), topiramate (Topamax), felbamate (Felbatol) and several others. Phenobarbital has been used as an anticonvulsant, and is still useful for some patients. The drugs are available only with a physician's prescription and come in tablet, capsule, liquid, and "sprinkle" forms.

Recommended dosage

The recommended dosage depends on the type of anticonvulsant, its strength, and the type of seizures for which it is being taken. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage.
Do not stop taking this medicine suddenly after taking it for several weeks or more. Gradually tapering the dose may reduce the chance of withdrawal effects.
Do not change brands or dosage forms of this medicine without checking with a pharmacist or physician. If a prescription refill does not look like the original medicine, check with the pharmacist who filled the prescription.


Patients on anticonvulsant drugs should see a physician regularly while on therapy, especially during the first few months. The physician will check to make sure the medicine is working as it should and will note unwanted side effects. The physician may also need to adjust the dosage during this period.

Key terms

Chronic — A word used to describe a long-lasting condition. Chronic conditions often develop gradually and involve slow changes.
Epilepsy — A brain disorder with symptoms that include seizures.
Glaucoma — A condition in which pressure in the eye is abnormally high. If not treated, glaucoma may lead to blindness.
Porphyria — A disorder in which porphyrins build up in the blood and urine.
Porphyrin — A type of pigment found in living things, such as chlorophyll which makes plants green or hemoglobin which makes blood red.
Seizure — A sudden attack, spasm, or convulsion.
Systemic lupus erythematosus (SLE) — A chronic disease with many symptoms, including weakness, fatigue, joint pain, sores on the skin, and problems with the kidneys, spleen, and other organs.
Withdrawal symptoms — A group of physical or mental symptoms that may occur when a person suddenly stops using a drug to which he or she has become dependent.
Valproic acid can cause serious liver damage, especially in the first 6 months of treatment. Children are particularly at risk, but anyone taking this medicine should see their physician regularly for tests of liver function and should be alert to symptoms of liver damage, such as yellow skin and eyes, facial swelling, loss of appetite, general feeling of illness, loss of appetite, and vomiting. If liver problems are suspected, call a physician immediately.
Felbatol has caused serious liver damage and aplastic anemia, a condition in which the bone marrow stops producing blood cells. Patients taking this drug should have regular blood counts, and should stop taking the drug if there are too few red blood cells.
While taking anticonvulsant drugs, do not start or stop taking any other medicines without checking with a physician. The other medicines may affect the way the anticonvulsant medicine works.
Because anticonvulsant drugs work on the central nervous system, they may add to the effects of alcohol and other drugs that slow down the central nervous system, such as antihistamines, cold medicine, allergy medicine, sleep aids, other medicine for seizures, tranquilizers, some pain relievers, and muscle relaxants. Anyone taking anticonvulsant drugs should check with his or her physician before drinking alcohol or taking any medicines that slow the central nervous system.
Anticonvulsant drugs may interact with medicines used during surgery, dental procedures, or emergency treatment. These interactions could increase the chance of side effects. Anyone who is taking anticonvulsant drugs should be sure to tell the health care professional in charge before having any surgical or dental procedures or receiving emergency treatment.
Some people feel drowsy, dizzy, lightheaded, or less alert when using these drugs, especially when they first begin taking them or when their dosage is increased. Anyone who takes anticonvulsant drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.
Anticonvulsant drugs may affect the results of certain medical tests. Before having medical tests, people who take anticonvulsant drugs should make sure that the medical professional in charge knows what they are taking.
Children may be more likely to have certain side effects from anticonvulsant drugs, such as behavior changes; tender, bleeding, or swollen gums; enlarged facial features; and excessive hair growth. Problems with the gums may be prevented by regularly brushing and flossing, massaging the gums, and having the teeth cleaned every 3 months whether the patient is a child or an adult.
Children who take high doses of this medicine for a long time may have problems in school.
Older people may be more sensitive to the effects of anticonvulsant drugs. This may increase the chance of side effects and overdoses.

Special conditions

People with certain medical conditions or who are taking certain other medicines can have problems if they take anticonvulsant drugs. Before taking these drugs, be sure to let the physician know about any of these conditions:
ALLERGIES. Anyone who has had unusual reactions to anticonvulsant drugs or to tricyclic antidepressants such as imipramine (Tofranil) or desipramine (Norpramin) in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.
PREGNANCY. Some anticonvulsant drugs taken during pregnancy may cause bleeding problems in the mother during delivery and in the baby after delivery. This problem can be avoided by giving vitamin K to the mother during delivery and to the baby after birth.
Pregnancy may affect the way the body absorbs anticonvulsant drugs. Women who are prone to seizures may have more seizures during pregnancy, even though they are taking their medicine regularly. If this happens, they should check with their physicians about whether the dose needs to be increased.
BREASTFEEDING. Some anticonvulsant drugs pass into breast milk and may cause unwanted effects in babies whose mothers take the medicine. Women who are breastfeeding should check with their physicians about the benefits and risks of using anticonvulsant drugs.
DIABETES. Anticonvulsant drugs may affect blood sugar levels. Patients with diabetes who notice changes in the results of their urine or blood tests should check with their physicians.
OTHER MEDICAL CONDITIONS. Before using anticonvulsant drugs, people with any of these medical problems should make sure their physicians are aware of their conditions:
  • liver disease
  • kidney disease
  • thyroid disease
  • heart or blood vessel disease
  • blood disease
  • brain disease
  • problems with urination
  • current or past alcohol abuse
  • behavior problems
  • diabetes mellitus
  • glaucoma
  • porphyria
  • systemic lupus erythematosus
  • fever higher than 101 °F (38.3 °C) for more than 24 hours
USE OF CERTAIN MEDICINES. Taking anticonvulsant drugs with certain other drugs may affect the way the drugs work or may increase the chance of side effects.

Side effects

The most common side effects are constipation, mild nausea or vomiting, and mild dizziness, drowsiness, or lightheadedness. These problems usually go away as the body adjusts to the drug and do not require medical treatment. Less common side effects, such as diarrhea, sleep problems, aching joints or muscles, increased sensitivity to sunlight, increased sweating, hair loss, enlargement of facial features, excessive hair growth, muscle twitching, and breast enlargement in males also may occur and do not need medical attention unless they persist or are troublesome.
Other side effects may need medical attention. If any of these side effects occur, check with a physician as soon as possible:
  • clumsiness or unsteadiness
  • slurred speech or stuttering
  • trembling
  • unusual excitement, irritability, or nervousness
  • uncontrolled eye movements
  • blurred or double vision
  • mood or mental changes
  • confusion
  • increase in seizures
  • bleeding, tender, or swollen gums
  • skin rash or itching
  • enlarged glands in neck or armpits
  • muscle weakness or pain
  • fever
Other side effects are possible. Anyone who has unusual symptoms after taking anticonvulsant drugs should get in touch with his or her physician.


Some anticonvulsant drugs should not be taken within two to three hours of taking antacids or medicine for diarrhea. These medicines may make the anticonvulsant drugs less effective. Ask the pharmacist or physician for more information.
Birth control pills may not work properly when anticonvulsant drugs are being taken. To prevent pregnancy, ask the physician or pharmacist if additional methods of birth control should be used while taking anticonvulsant drugs.
Anticonvulsant drugs may interact with many other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes anticonvulsant drugs should let the physician know all other medicines he or she is taking. Among the drugs that may interact with certain anticonvulsant drugs are:
  • airway opening drugs (bronchodilators) such as aminophylline, theophylline (Theo-Dur and other brands), and oxtriphylline (Choledyl and other brands)
  • medicines that contain calcium, such as antacids and calcium supplements
  • blood thinning drugs
  • caffeine
  • antibiotics such as clarithromycin (Biaxin), erythromycins, and sulfonamides (sulfa drugs)
  • disulfiram (Antabuse), used to treat alcohol abuse
  • fluoxetine (Prozac)
  • monoamine oxidase inhibitors (MAO inhibitors) such as phenelzine (Nardil) or tranylcypromine (Parnate), used to treat conditions including depression and Parkinson's disease
  • tricyclic antidepressants such as imipramine (Tofranil) or desipramine (Norpramin)
  • corticosteroids
  • acetaminophen (Tylenol)
  • aspirin
  • female hormones (estrogens)
  • male hormones (androgens)
  • cimetidine (Tagamet)
  • central nervous system (CNS) depressants such as medicine for allergies, colds, hay fever, and asthma; sedatives; tranquilizers; prescription pain medicine; muscle relaxants; medicine for seizures; sleep aids; barbiturates; and anesthetics
  • alcohol
  • other anticonvulsant drugs
The list above does not include every drug that may interact with anticonvulsant drugs. Be sure to check with a physician or pharmacist before combining anticonvulsant drugs with any other prescription or nonprescription (over-the-counter) medicine.



Reynolds, E.H. "Do Anticonvulsant Drugs Alter the Natural Course of Epilepsy? Treatment Should Be Started as Early as Possible." British Medical Journal 310 (January 21, 1995): 176.


American Epilepsy Society. 638 Prospect Avenue, Hartford, CT 06105. (203) 232-4825.
Epilepsy Foundation of America. 4351 Garden City Drive, #406, Landover, MD 20785. (800) 332-1000.
National Institute of Neurological Disorders and Stroke. P.O. Box 5801, Bethesda, MD 20824. (301) 496-5751.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

Anticonvulsant Drugs: Carbamazepine, Ethosuximide, Lamotrigine, Phenobarbital, Phenytoin, Primidone, Valproic Acid

Synonym/acronym: Carbamazepine (Carbamazepinum, Carbategretal, Carbatrol, Carbazep, CBZ, Epitol, Tegretol, Tegretol XR); ethosuximide (Suxinutin, Zarontin, Zartalin); lamotrigine (Lamictal) phenobarbital (Barbita, Comizial, Fenilcal, Gardenal, Phenemal, Phenemalum, Phenobarb, Phenobarbitone, Phenylethylmalonylurea, Solfoton, Stental Extentabs); phenytoin (Antisacer, Dilantin, Dintoina, Diphenylan Sodium, Diphenylhydantoin, Ditan, Epanutin, Epinat, Fenitoina, Fenytoin, Fosphenytoin); primidone (Desoxyphenobarbital, Hexamidinum, Majsolin, Mylepsin, Mysoline, Primaclone, Prysolin); valproic acid (Depacon, Depakene, Depakote, Depakote XR, Depamide, Dipropylacetic Acid, Divalproex Sodium, Epilim, Ergenyl, Leptilan, 2–Propylpentanoic Acid, 2–Propylvaleric Acid, Valkote, Valproate Semisodium, Valproate Sodium).

Common use

To monitor specific drugs for subtherapeutic, therapeutic, or toxic levels in evaluation of treatment.


Serum (1 mL) collected in a red-top tube.
Drug*Route of Administration
Valproic acidOral
*Recommended collection time = trough: immediately before next dose (at steady state) or at a consistent sampling time.

Normal findings

(Method: Immunoassay for all except lamotrigine; liquid chromatography/tandem mass spectrometry for lamotrigine)
DrugTherapeutic Range Conventional UnitsConversion to SI unitsTherapeutic Range SI UnitsHalf-Life (hr)Volume of Distribution (L/kg)Protein Binding (%)Excretion
Carbamazepine4–12 mcg/mLSI units = Conventional Units × 4.2317–51 micromol/L15–400.8–1.860–80Hepatic
Ethosuximide40–100 mcg/mLSI units = Conventional Units × 7.08283–708 micromol/L25–700.70–5Renal
Lamotrigine1–4 mcg/mLSI units = Conventional Units × 3.94–16 micromol/L25–330.9–1.350–5Hepatic
PhenobarbitalAdult: 15–40 mcg/mLSI units = Conventional Units × 4.31Adult: 65–172 micromol/LAdult: 50–1400.5–140–5080% Hepatic and 20% Renal
Child: 15–30 mcg/mLSI units = Conventional Units × 4.31Child: 65–129 micromol/LChild: 40–7080% Hepatic and 20% Renal
Phenytoin10–20 mcg/mLSI units = Conventional Units × 3.9640–79 micromol/L20–400.6–0.785–95Hepatic
PrimidoneAdult: 5–12 mcg/mLSI units = Conventional Units × 4.58Adult: 23–55 micromol/L4–120.5–10–20Hepatic
Child: 7–10 mcg/mLSI units = Conventional Units × 4.58Child: 32–46 micromol/L
Valproic acid50–125 mcg/mLSI units = Conventional Units × 6.93347–866 micromol/L8–150.1–0.585–95Hepatic


Anticonvulsants are used to reduce the frequency and severity of seizures for patients with epilepsy. Carbamazepine is also used for controlling neurogenic pain in trigeminal neuralgia and diabetic neuropathy and for treating bipolar disease and other neurological and psychiatric conditions. Valproic acid is also used for some psychiatric conditions like bipolar disease and for prevention of migraine headache.

Many factors must be considered in effective dosing and monitoring of therapeutic drugs, including patient age, patient weight, interacting medications, electrolyte balance, protein levels, water balance, conditions that affect absorption and excretion, and the ingestion of substances (e.g., foods, herbals, vitamins, and minerals) that can either potentiate or inhibit the intended target concentration. Peak and trough collection times should be documented carefully in relation to the time of medication administration.

The metabolism of many commonly prescribed medications is driven by the cytochrome P450 (CYP450) family of enzymes. Genetic variants can alter enzymatic activity that results in a spectrum of effects ranging from the total absence of drug metabolism to ultrafast metabolism. Impaired drug metabolism can prevent the intended therapeutic effect or even lead to serious adverse drug reactions. Poor metabolizers (PM) are at increased risk for drug-induced side effects due to accumulation of drug in the blood, while ultra-rapid metabolizers (UM) require a higher than normal dosage because the drug is metabolized over a shorter duration than intended. In the case of pro-drugs, which require activation prior to metabolism, the opposite occurs: PM may require a higher dose because the activated drug becomes available more slowly than intended, and UM requires less because the activated drug becomes available sooner than intended. Other genetic phenotypes used to report CYP450 results are intermediate metabolizer (IM) and extensive metabolizer (EM). Genetic testing can be performed on blood samples submitted to a laboratory. The test method commonly used is polymerase chain reaction. Counseling and informed written consent are generally required for genetic testing. CYP2C9 is a gene in the CYP450 family that metabolizes pro-drugs like phenytoin as well as other drugs like phenobarbital; the anticoagulant warfarin; and opioid analgesics like codeine, hydrocodone, dihydrocodeine, oxycodone, and tramadol. Testing for the most common genetic variants of CYP2C9 is used to predict altered enzyme activity and anticipate the most effective therapeutic plan. Incidence of the PM phenotype is estimated to be less than 0.04% of African Americans and less than 0.1% of Caucasians and Asians.

Important note:

These medications are metabolized and excreted by the liver and kidneys and are therefore contraindicated in patients with hepatic or renal disease. Caution is advised for patients with renal impairment. Information regarding medications must be clearly and accurately communicated to avoid misunderstanding of the dose time in relation to the collection time. Miscommunication between the individual administering the medication and the individual collecting the specimen is the most frequent cause of subtherapeutic levels, toxic levels, and misleading information used in calculation of future doses. If administration of the drug is delayed, notify the appropriate department(s) to reschedule the blood draw and notify the requesting health-care provider (HCP) if the delay has caused any real or perceived therapeutic harm.

This procedure is contraindicated for



  • Assist in the diagnosis of and prevention of toxicity
  • Evaluate overdose, especially in combination with ethanol
  • Monitor compliance with therapeutic regimen

Potential diagnosis

Normal levelsTherapeutic effect
Subtherapeutic levelsAdjust dose as indicated
Toxic levelsAdjust dose as indicated
 CarbamazepineHepatic impairment
 EthosuximideRenal impairment
 LamotrigineHepatic impairment
 PhenobarbitalHepatic or renal impairment
 PhenytoinHepatic impairment
 PrimidoneHepatic impairment
 Valproic acidHepatic impairment

Critical findings

  • It is important to note the adverse effects of toxic and subtherapeutic levels. Care must be taken to investigate signs and symptoms of not enough medication and too much medication. Note and immediately report to the HCP any critically increased or subtherapeutic values and related symptoms.

  • It is essential that a critical finding be communicated immediately to the requesting HCP. A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. The notification processes will vary among facilities. Upon receipt of the critical finding the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical finding, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

  • Carbamazepine: Greater Than 20 mcg/mL (SI: Greater Than 85 micromol/L)

  • Signs and symptoms of carbamazepine toxicity include respiratory depression, seizures, leukopenia, hyponatremia, hypotension, stupor, and possible coma. Possible interventions include gastric lavage (contraindicated if ileus is present); airway protection; administration of fluids and vasopressors for hypotension; treatment of seizures with diazepam, phenobarbital, or phenytoin; cardiac monitoring; monitoring of vital signs; and discontinuing the medication. Emetics are contraindicated.

  • Ethosuximide: Greater Than 200 mcg/mL (SI: Greater Than 1,416 micromol/L)

  • Signs and symptoms of ethosuximide toxicity include nausea, vomiting, and lethargy. Possible interventions include administration of activated charcoal, administration of saline cathartic and gastric lavage (contraindicated if ileus is present), airway protection, hourly assessment of neurologic function, and discontinuing the medication.

  • Lamotrigine: Greater Than 20 mcg/mL (SI: Greater Than 78 micromol/L)

  • Signs and symptoms of lamotrigine toxicity include severe skin rash, nausea, vomiting, ataxia, decreased levels of consciousness, coma, increased seizures, nystagmus. Possible interventions include administration of activated charcoal, administration of saline cathartic and gastric lavage (contraindicated if ileus is present), airway protection, hourly assessment of neurologic function, and discontinuing the medication

  • Phenobarbital: Greater Than 60 mcg/mL (SI: Greater Than 259 micromol/L)

  • Signs and symptoms of phenobarbital toxicity include cold, clammy skin; ataxia; central nervous system (CNS) depression; hypothermia; hypotension; cyanosis; Cheyne-Stokes respiration; tachycardia; possible coma; and possible renal impairment. Possible interventions include gastric lavage, administration of activated charcoal with cathartic, airway protection, possible intubation and mechanical ventilation (especially during gastric lavage if there is no gag reflex), monitoring for hypotension, and discontinuing the medication.

  • Phenytoin (Adults): Greater Than 40 mcg/mL (SI: Greater Than 158 micromol/L)

  • Signs and symptoms of phenytoin toxicity include double vision, nystagmus, lethargy, CNS depression, and possible coma. Possible interventions include airway support, electrocardiographic monitoring, administration of activated charcoal, gastric lavage with warm saline or tap water, administration of saline or sorbitol cathartic, and discontinuing the medication.

  • Primidone: Greater Than 15 mcg/mL (SI: Greater Than 69 micromol/L)

  • Signs and symptoms of primidone toxicity include ataxia, anemia, CNS depression, lethargy, somnolence, vertigo, and visual disturbances. Possible interventions include airway protection, treatment of anemia with vitamin B12 and folate, and discontinuing the medication.

  • Valproic Acid: Greater Than 200 mcg/mL (SI: Greater Than 1,386 micromol/L)

  • Signs and symptoms of valproic acid toxicity include loss of appetite, mental changes, numbness, tingling, and weakness. Possible interventions include administration of activated charcoal and naloxone and discontinuing the medication.

Interfering factors

  • Blood drawn in serum separator tubes (gel tubes).
  • Drugs that may increase carbamazepine levels or increase risk of toxicity include acetazolamide, azithromycin, bepridil, cimetidine, danazol, diltiazem, erythromycin, felodipine, fluoxetine, flurithromycin, fluvoxamine, gemfibrozil, isoniazid, itraconazole, josamycin, ketoconazole, loratadine, macrolides, niacinamide, nicardipine, nifedipine, nimodipine, nisoldipine, propoxyphene, ritonavir, terfenadine, troleandomycin, valproic acid, verapamil, and viloxazine.
  • Drugs that may decrease carbamazepine levels include phenobarbital, phenytoin, and primidone.
  • Carbamazepine may affect other body chemistries as seen by a decrease in calcium, sodium, T3, T4 levels, and WBC count and increase in ALT, alkaline phosphatase, ammonia, AST, and bilirubin levels.
  • Drugs that may increase ethosuximide levels include isoniazid, ritonavir, and valproic acid.
  • Drugs that may decrease ethosuximide levels include phenobarbital, phenytoin, and primidone.
  • Drugs that may increase lamotrigine levels include valproic acid.
  • Drugs that may decrease lamotrigine levels include acetaminophen, carbamazepine, hydantoins (e.g., phenytoin), oral contraceptives, orlistat, oxcarbazepine, phenobarbital, primidone, protease inhibitors (e.g., ritonavir), rifamycins (e.g., rifampin), and succinimides (e.g., ethosuximide).
  • Drugs that may increase phenobarbital levels or increase risk of toxicity include barbital drugs, furosemide, primidone, salicylates, and valproic acid.
  • Phenobarbital may affect the metabolism of other drugs, increasing their effectiveness, such as β-blockers, chloramphenicol, corticosteroids, doxycycline, griseofulvin, haloperidol, methylphenidate, phenothiazines, phenylbutazone, propoxyphene, quinidine, theophylline, tricyclic antidepressants, and valproic acid.
  • Phenobarbital may affect the metabolism of other drugs, decreasing their effectiveness, such as chloramphenicol, cyclosporine, ethosuximide, oral anticoagulants, oral contraceptives, phenytoin, theophylline, vitamin D, and vitamin K.
  • Phenobarbital is an active metabolite of primidone, and both drug levels should be monitored while the patient is receiving primidone to avoid either toxic or subtherapeutic levels of both medications.
  • Phenobarbital may affect other body chemistries as seen by a decrease in bilirubin and calcium levels and increase in alkaline phosphatase, ammonia, and gamma glutamyl transferase levels.
  • Drugs that may increase phenytoin levels or increase the risk of phenytoin toxicity include amiodarone, azapropazone, carbamazepine, chloramphenicol, cimetidine, disulfiram, ethanol, fluconazole, halothane, ibuprofen, imipramine, levodopa, metronidazole, miconazole, nifedipine, phenylbutazone, sulfonamides, trazodone, tricyclic antidepressants, and trimethoprim. Small changes in formulation (i.e., changes in brand) also may increase phenytoin levels or increase the risk of phenytoin toxicity.
  • Drugs that may decrease phenytoin levels include bleomycin, carbamazepine, cisplatin, disulfiram, folic acid, intravenous fluids containing glucose, nitrofurantoin, oxacillin, rifampin, salicylates, and vinblastine.
  • Primidone decreases the effectiveness of carbamazepine, ethosuximide, felbamate, lamotrigine, oral anticoagulants, oxcarbazepine, topiramate, and valproate.
  • Primidone may affect other body chemistries as seen by a decrease in calcium levels and increase in alkaline phosphatase levels.
  • Drugs that may increase valproic acid levels or increase risk of toxicity include dicumarol, phenylbutazone, and high doses of salicylate.
  • Drugs that may decrease valproic acid levels include carbamazepine, phenobarbital, phenytoin, and primidone.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist with monitoring for subtherapeutic, therapeutic, or toxic drug levels.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • These medications are metabolized and excreted by the kidneys and liver. Obtain a history of the patient’s genitourinary and hepatobiliary systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Note the last time and dose of medication taken.
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications:
  • Lack of consideration for the proper collection time relative to the dosing schedule can provide misleading information that may result in erroneous interpretation of levels, creating the potential for a medication-error-related injury to the patient.

  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Consider recommended collection time in relation to the dosing schedule. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection, noting the last dose of medication taken. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Nutritional Considerations: Antiepileptic drugs antagonize folic acid, and there is a corresponding slight increase in the incidence of fetal malformations in children of epileptic mothers. Women of childbearing age who are taking carbamazepine, phenobarbital, phenytoin, primadone, and/or valproic acid should also be prescribed supplemental folic acid to reduce the incidence of neural tube defects. Neonates born to epileptic mothers taking antiseizure medications during pregnancy may experience a temporary drug-induced deficiency of vitamin K–dependent coagulation factors. This can be avoided by administration of vitamin K to the mother in the last few weeks of pregnancy and to the infant at birth.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Explain to the patient the importance of following the medication regimen and instructions regarding drug interactions. Instruct the patient to immediately report any unusual sensations (e.g., ataxia, dizziness, dyspnea, lethargy, rash, tremors, mental changes, weakness, or visual disturbances) to his or her HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Instruct the patient to be prepared to provide the pharmacist with a list of other medications he or she is already taking in the event that the requesting HCP prescribes a medication.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ALT, albumin, AST, bilirubin, BUN, creatinine, electrolytes, GGT, and protein blood total and fractions.
  • See the Genitourinary and Hepatobiliary systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners
References in periodicals archive ?
Out of all patients of exfoliative dermatitis, 66.7% had history of taking indigenous drugs, and 16.7% had anticonvulsant drugs and quinolone intake history.
The anticonvulsant drugs increased the worms' motility and stimulated egg laying, suggesting that the chemicals interact with C.
Anticonvulsant drugs and malformations: is there a drug specificity?
Administration of gabapentin does not influence the pharmacokinetics of conventional anticonvulsant drugs, nor are the pharmacokinetics of gabapentin modified by the presence of other anticonvulsant drugs (1).
One case was born with foetal alcohol syndrome and another was linked to anticonvulsant drugs taken by the mother during pregnancy for epilepsy.
Among the group who had continued to take the same anticonvulsant drugs throughout their pregnancies, 18 babies had serious abnormalities.
Researchers say that infants of mothers with epilepsy who took no anticonvulsant drugs during the pregnancy did not have a higher frequency of major malformations, slow growth, and undeveloped face and fingers.
Pharmacologic treatment with anxiolytics, antidepressants, and anticonvulsant drugs was successful in alleviating symptoms in three patients.
* therapy with multiple anticonvulsant drugs, including valproate;
Because he had suddenly stopped his anticonvulsant drugs, he experienced several severe seizures producing a painful recurrent shoulder dislocation.
Like other anticonvulsant drugs, carbamazepine acts by suppressing electrical activity in the brain.