Carbamazepin

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 stabilize the moods of patients with bipolar disease and to help alleviate some types of nerve pain (e.g trigeminal neuralgia). It may be prescribed by itself or in combination with other antiepileptic drugs.

Carbamazepine levels are monitored because the drug must be maintained within a relatively narrow concentration range. If the level is too low, the patient may experience a recurrence of symptoms (i.e. seizures, mania, or pain) and if the level is too high, the patient may experience increased toxic side effects. This balance can be difficult to achieve for several different reasons:

• Oral doses of carbamazepine are absorbed in the stomach and intestine at widely variable rates.
• Since carbamazepine is metabolised by the liver, anything that affects the function of the liver can affect blood levels of the drug.
• Much of the drug is bound to proteins in the blood plasma, but it is the free portion of the drug that has the therapeutic effect. Conditions that affect the extent of protein binding of the drug may affect therapeutic effectiveness.
• The product of carbamazepine metabolism, carbamazepine-10,11 epoxide, is also an active compound and contributes to the overall effect of the medication.
• Several drugs, if taken in conjunction with carbamazepine, may alter the effect 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 required to reach this steady state will vary from person to person and may change over time.

Carbamazepine is usually monitored long-term because it is prescribed for chronic conditions which require long-term treatment. Seizure disorders affect the brain’s ability to transmit electrical impulses and to regulate nerve activity. During a seizure, a patient may experience changes in consciousness, alterations in sight, smell, and taste, and may experience convulsions (fits). Seizures are associated with acute conditions, such as high fevers and head trauma, and with chronic conditions such as metabolic disorders and brain tumours. In many cases, the cause is not known. The frequency of seizures varies from a single episode, to occasional seizures, to recurrent seizures. Seizures are categorised by the parts of the brain and body that are affected.  Carbamazepine is prescribed to help prevent specific types of recurrent seizures, particularly those unresponsive to lithium.

Bipolar disorder is a psychiatric condition that is characterised by cycles of depression and mania that may last for days, weeks, months, or years. During a depressive episode those affected may feel sad, hopeless, worthless, and have thoughts of suicide. During a manic episode, those affected may be extremely happy and excited, irritable, have poor judgment, and participate in risky behaviour. 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, and paroxysmal choreoathetosis are also sometimes treated with carbamazepine.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.