Carbamazepine

Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.

The carbamazepine test is performed on a blood sample to measure the level of the antiepileptic drug carbamazepine in the bloodstream. It is used to help monitor therapeutic drug levels to ensure effective seizure control while avoiding toxicity, and to assess adherence or dose adjustment needs.

Also known as 
Tegretol®; Carbagen SR 
Formal name 
Carbamazepine (total)

Why get tested?

To determine the concentration of carbamazepine in the blood to establish an appropriate dose and to maintain a therapeutic level

When to get tested?

At the beginning of treatment to monitor the concentration of the drug in the blood.
When indicated to detect low or high (potentially toxic) concentrations.

Sample required?

A blood sample taken from a vein in your arm

Test preparation needed?

No test preparation is needed.

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 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.

The dose 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.

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, particularly those unresponsive to lithium.

Trigeminal neuralgia, a condition associated with facial nerve pain and muscle spasms, and paroxysmal choreoathetosis are also sometimes treated with carbamazepine. It is also sometimes used in the treatment of acute alcohol withdrawal (unlicensed use in the UK).

Common questions