Serum Carbamazepine (Tegretol)

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Test

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

When this test is required

Carbamazepine tests are requested frequently on commencing treatment, then as needed to ensure that appropriate blood concentrations are maintained. Additional carbamazepine tests may be requested if the dose of the drug is changed, if a patient starts or stops taking additional medications (to judge their effect, if any, on carbamazepine levels), or if a patient has a recurrence of symptoms such as a seizure, nerve pain, or bipolar mood swings. Once blood concentrations of carbamazepine have stabilized, concentration monitoring may not be necessary, but levels are sometimes monitored at regular intervals to ensure that they remain within the therapeutic range.The carbamazepine test may also be requested when a patient’s condition does not appear to be responding to therapy. This may be because concentrations are not be high enough, because the patient may not be taking the medication regularly, or the drug may be ineffective for that person.Carbamazepine tests may also be requested when a patient experiences a troublesome level of side effects and/or develops complications. Side effects that may be seen at any dose but are related to higher concentrations include Dizziness Dry mouth Fatigue Uncoordinated movement Sleepiness Blurred or double vision Nystagmus— an involuntary movement of the eyeballOther side effects may include: A red itchy rash Nausea Diarrhoea Constipation Headache Confusion Vision disordersCarbamazepine can also sometimes cause liver function abnormalities, low blood sodium concentrations, a decrease in white blood cells (WBCs) or an increase in eosinophils (a type of WBC). In some cases, the severity of side effects may cause the patient and doctor to select a different medication for the disorder being treated.Some individuals of Han Chinese or Thai origin are at increased risk of a serious skin disorder (Stevens-Johnson syndrome) if prescribed carbamazepine and the drug should be avoided unless there is no alternative. The HLA-B*1502 test may be used to assess susceptibility in such individuals.Carbamazepine should not be used in acute porphyria.Patients should talk to their doctor about the timing of the sample collection. Often, the recommended time is just before the next dose is taken (“trough level”, when concentrations are at their lowest).

What the Test Detects

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…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). See MoreSee Less

Preparation for the Test

No test preparation is needed.

Sample Requirements

A blood sample taken from a vein in your arm

Additional Notes

Carbamazepine can affect or be affected by many prescribed and over-the-counter medications – such as paracetamol, warfarin, fluconazole, isoniazid, theophylline, erythromycin, , the combined oral contraceptive pill and immunosuppressant drugs (ciclosporin, sirolimus, tacrolimus). Also, the metabolism of carbamazepine can be increased by other antiepileptic drugs such as phenobarbital, primidone and phenytoin. The effect of this increased metabolism is to decrease carbamazepine concentrations in the blood. Some of these drugs may also require monitoring with blood tests. Herbal supplements, such as St. John’s Wort, can also affect carbamazepine concentrations. Tell your doctor about all medication and supplements that you are taking. Further information on drug interactions is available on the NICE BNF web site.Carbamazepine can increase the risk of certain birth defects and foetal death, and can decrease the effectiveness of oral contraceptives. Women of childbearing age should talk to their doctors about this.

Selected Tests