The valproic acid test is sometimes used to measure and monitor the amount of valproic acid in the blood to find out whether drug levels are appropriate. The amount of the drug taken may be changed depending on the results of the blood test. The test may then be checked occasionally to ensure that therapeutic blood levels are maintained. One or more valproic acid tests may be requested if a patient starts or stops taking additional medications (to judge their effect, if any, on valproic acid levels) and may be used if the patient has a recurrence of symptoms such as a seizure, a migraine, or experiences bipolar mood swings. Doctors will also evaluate their patient for side effects and adverse reactions during initial dosage adjustments and over time. These side effects may include some or a combination of the following:
Gastrointestinal symptoms such as nausea, vomiting, diarrhoea
Unusual weight gain or loss
Drowsiness or lethargy
Unusual bruising and bleeding
Rare complications such as liver dysfunction or pancreatitis
Very young and elderly patients are more likely to experience increased side effects. In some cases, the severity of side effects may cause the patient and doctor to seek an alternative medicine.
Routine monitoring is generally unnecessary, but a valproic acid level may be requested when a patient begins valproic acid treatment and when/if a patient’s drugs are started, stopped, or changed.
The test may be requested when a patient’s condition does not appear to be responding to valproic acid to find out whether levels are too low, the medicine is ineffective, and/or to find out if the patient is taking the prescribed dose of valproic acid regularly. It may also be requested when a patient experiences a troublesome level of side effects and/or develops complications.
Patients should talk to their doctor about the timing of the sample collection. Since dosage timing varies, and some formulations of the drug release the drug slowly over time, times of specimen collection may vary. Often, the recommended time for sample collection is just before the next dose is taken (trough level). This ensures that the minimum amount of drug to be effective is maintained in the blood.
The appropriate range for valproic acid in the blood is usually taken as 50 - 120 µg/mL. Within this range, most people will respond to the drug without excessive side effects; however, response varies with each individual. Some people will experience seizures, mood swings, or migraines at the low end of the therapeutic range while some people will experience excessive side effects at the upper end. Patients should work closely with their doctor to find the dose and level that works the best for them.
In general, if valproic acid results are within the target range, the patient is not having recurrent seizures, mood swings, or migraines, and the patient is not experiencing significant side effects, then the dosage of valproic acid a patient is receiving is considered adequate. Patients should not increase, decrease, or stop taking their medication without consulting with their doctor as it can increase their risk of having a seizure and may affect other medications that they are taking. Dose adjustments must be made on a case-by-case basis.
Valproic acid reduces the breakdown of other seizure medicines such as carbamazepine, phenytoin, lamotrigine, and phenobarbital, and increase their levels in the blood. If a patient is on additional drugs such as these, they may occasionally need to be monitored with blood tests.
While severe liver injury is rare, mild increases in enzymes (AST and ALT) which come from the liver occur in up to 20% of those taking valproic acid; these usually return to normal even if the drug is continued.
The babies of women who use valproic acid during pregnancy are at an increased risk of developing several birth defects. Since this drug increases the risk of neural tube defects such as spina bifida, women of child-bearing age who want to become pregnant should talk to their doctors about this subject.
A variety of prescribed drugs, over-the-counter medicine, and supplements can increase, decrease, or interfere with the concentrations of valproic acid in the blood. Patients should talk to their doctors about all of the drugs and supplements that they are taking and about the medicines that are right for them. Valproic acid is not effective for every kind of seizure and will not work for every patient.
This article was last reviewed on 26 April 2011. | This article was last modified on 26 October 2011.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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