At a Glance
Why Get Tested?
To determine the concentration of carbamazepine in the blood and to maintain a therapeutic level
When to Get Tested?
At regular intervals to monitor the drug’s level; when indicated to detect low or excessive (potentially toxic) concentrations
A blood sample drawn from a vein in your arm
The Test Sample
What is being tested?
This test measures the amount of carbamazepine in the blood. Carbamazepine is a drug that is primarily used to treat certain seizure disorders (also called epilepsy) but is also prescribed to stabilise the moods of patients with bipolar disease and to help alleviate some types of nerve pain. It may be prescribed by itself or in combination with other antiepileptic drugs. Seizure disorders affect the brain's ability to transmit electrical impulses and to regulate nerve activity. Carbamazepine is prescribed to help prevent specific types of recurrent seizures.
Bipolar disorder is a mental condition that is characterised by cycles of depression and mania that may last for days, weeks, months, or years. Carbamazepine is prescribed to help even out the moods of the person with bipolar disorder, especially mania.
Trigeminal neuralgia, a condition associated with facial nerve pain and muscle spasms is also sometimes treated with carbamazepine.
Carbamazepine is sometimes used to treat the alcohol withdrawal sydrome.
Carbamazepine levels are monitored because the drug must be maintained within a narrow therapeutic range. If levels are too low, the patient may experience a recurrence of symptoms (i.e. seizures, mania or pain); too high of a level and the patient may experience increased toxic side effects.
This balance can be a challenge to achieve for several different reasons:
- Oral doses of carbamazepine are absorbed in the gastrointestinal tract at widely variable rates.
- Since carbamazepine is metabolised by the liver, anything that affects liver function can affect blood levels of the drug.
- Much of the drug is bound to plasma protein, but it is the free portion of the drug that is active. Conditions that affect protein binding of the drug may affect therapeutic effectiveness.
- The metabolite of carbamazepine, carbamazepine-10 11 epoxide, is also active and contributes to the overall effect of the medication.
- Several drugs, if taken in conjunction with carbamazepine, may interact or affect metabolism and blood levels.
Dosages of carbamazepine must be adjusted carefully until a steady concentration in the blood is reached. The actual amount of drug that it takes to reach this steady state will vary from person to person and may change over time.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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