Other names: Phenobarbitone

Phenobarbital is a drug, which is used to depress the nervous system; it is a barbiturate, which is prescribed to people with severe anxiety and seizure disorders, such as epilepsy. The drug works by regulating electrical activity in the brain.

When is the test used?

The test is used primarily to monitor the levels of Phenobarbital in the blood; it is important to monitor the levels to ensure the patient does not suffer symptoms of toxicity. The drug must be given in suitable doses to prevent toxicity and ensure that there is enough medication in the blood to work effectively.

The test is usually ordered once a patient has started taking the drug; the test helps doctors to assess whether the dose is right for the patient. The test may also be ordered if the patient is already taking medication and the doctor wants them to start taking Phenobarbital; many different types of medication react with Phenobarbital, including antidepressants, blood thinning medication, oral contraceptives and antihistamines.

If the levels of medication are too low, the drug may not work effectively and the patient may still experience seizures; if levels are too high, this may lead to symptoms of toxicity, including seizures, unusual bleeding, fever, sore throat and severe skin irritation.

How is the test carried out?

The test is done by taking a blood sample of a vein in the arm; a needle in inserted into the vein and the blood is drawn out and collected in the syringe. When a sufficient sample has been collected, the blood will be bottled, labelled with the patient’s name and sent away for analysis at the laboratory.

What do the test results mean?

The target range for Phenobarbital is between 15 and 40 mg/L; if the test result shows that the level is within this target range, the dose should be working effectively and the patient should not be suffering any unpleasant side-effects.

If the test result shows that the level is lower than the target range, this indicates that the dosage is too low and the drug may not be working effectively; the patient may still be suffering from seizures. The doctor will probably increase the dosage if the test result is low.

If the result shows that the level of Phenobarbital is too high, this may mean that the patient is receiving too much of the drug; this may cause symptoms of toxicity. In some cases, a high dose may be very dangerous and could potentially be life-threatening. If the test result is too high, the doctor will lower the dose.

Specific Blood Tests

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