The valproic acid test is ordered to measure and monitor the amount of valproic acid in the blood to determine whether drug concentrations are in the therapeutic range. The prescribed dose of the drug may be adjusted up or down depending on the results of the blood test. The test may then be ordered at regular intervals, and as needed, to ensure that therapeutic blood concentrations are maintained. One or more valproic acid tests may be ordered if a patient starts or stops taking additional medications (to judge their effect, if any, on valproic acid levels) and may be ordered 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, diarrhea

Dizziness

Unusual weight gain or loss

Tremors

Blurred or double vision, uncontrolled eye movements

Mood swings

Unusual bruising and bleeding

Hives

Hair loss

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 another anti-seizure, bipolar, or migraine medication.

A valproic acid level is ordered when a patient begins valproic acid treatment and when/if a patient’s medications change (other drugs are started, stopped, or changed). Once stable blood concentrations in the therapeutic range have been achieved, valproic acid levels may then be monitored at regular intervals to ensure that it remains within this range.

The test may be ordered when a patient’s condition does not appear to be responding to valproic acid to determine whether concentrations are too low, the medication is ineffective, and/or to determine if the patient is complying with therapy (taking the valproic acid regularly). It may also be ordered 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 are time released, collection specifics 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 therapeutic range for valproic acid has been established at 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 dosage and concentration that works the best for them.

In general, if valproic acid results are within the therapeutic 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. Dosage determinations and adjustments must be evaluated on a case-by-case basis.

Valproic acid inhibits the metabolism of other seizure medications such as carbamazepine, phenytoin, lamotrigine, and phenobarbital, increasing their concentrations in the blood. If a patient is on additional drugs such as these, they may also need to be monitored with blood tests.

While severe liver injury is rare, mild increases in liver-related enzymes (AST and ALT) occur in up to 20% of those taking valproic acid; these usually return to normal even if the drug is continued.

The fetus 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 medications, 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 medication(s) that are right for them. Valproic acid is not effective for every kind of seizure and will not work for every patient.