Carbamazepine Toxicity Workup

Updated: Apr 29, 2020
  • Author: Muhammad Waseem, MBBS, MS, FAAP, FACEP, FAHA; Chief Editor: Stephen L Thornton, MD  more...
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Workup

Laboratory Studies

The workup in a patient with suspected carbamazepine poisoning should include appropriate comprehensive serum and urine drug screening, plus analysis of the following:

  • Alcohol level, if alcohol toxicity is suspected.

  • Serum electrolyte levels, including glucose, calcium, magnesium, phosphate, serum bicarbonate, blood urea nitrogen (BUN), and serum creatinine levels; hyponatremia can be seen with long-term use [24]  but rarely is noted in acute overdose.

  • Liver function tests, because elevated liver enzyme levels, hepatitis, and hyperammonemia may be noted with chronic toxicity

Serum drug testing should be based on the history of ingestion and/or the patient’s toxidrome.

A serum and urine drug screen may not detect carbamazepine; therefore, the serum carbamazepine level should also be determined if the patient has access to carbamazepine. Structural similarity between carbamazepine and tricyclic antidepressants (TCAs) may cause false-positive results with immunoassay for TCAs. Patients who are taking carbamazepine should have therapeutic drug monitoring using serum carbamazepine levels. [25]

Because carbamazepine absorption varies, the serum concentration may not peak for as long as 24-72 hours. With controlled-release formulation, levels may continue to rise until 4 days postingestion. In fact, the initial carbamazepine level may be misleading. For this reason, serial measurements documenting a declining carbamazepine level and prolonged observation are recommended when managing these overdoses. [26]

Initial serum levels of more than 35 mg/L (127 µmol/L) suggest serious toxicity. However, lower initial serum levels do not necessarily indicate a benign course and the patient still needs to be closely monitored for signs and symptoms of significant toxicity.

The serum concentration may not always directly correlate with the clinical picture. The severity of toxicity is assessed on the basis of the clinical status and not only the serum carbamazepine concentration.

Toxicity may result from carbamazepine itself or its active epoxide metabolite. However, measuring epoxide levels along with the carbamazepine level provides no additional advantage.

The complete blood cell count (CBC) with a differential should be obtained. Rarely, hematologic adverse effects, including agranulocytosis, thrombocytopenia, and aplastic anemia, have been reported with long-term carbamazepine use. [27]

Although in utero exposure to carbamazepine has not been associated with adverse neuropsychological function, it has been associated with reduced verbal abilities.Therefore, a urine pregnancy test should be obtained on adolescent girls and women and if they are pregnant they should be counseled as to the possible effects of carbamazepine on the development of the fetus. [28]

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Imaging Studies

Obtain an abdominal radiograph, because patients with rising serum levels may have a bezoar of undigested tablets that may be visualized radiographically.

Obtain a chest radiograph if crackles or rales are heard on physical examination and pulmonary edema is suspected or to confirm endotracheal (ET) placement if respiratory depression occurs.

Computed tomography of the head maybe warranted as part of evaluation for altered mental status.

With acute carbamazepine toxicity, ultrasonography may reveal chemical pancreatitis. These patients may have no accompanying pain or other signs and symptoms.

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Other Tests

Obtain a 12-lead electrocardiogram (ECG). Abnormalties found may include the following [8] :

  • QRS widening
  • Sinus tachycardia
  • Varying degrees of atrioventricular block
  • QT prolongation

Carbamazepine is incorporated and retained in hair, depending on the blood levels. Sectional hair analysis can help investigators determine if chronic poisoning is an issue. [29]

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