Top 10 Common Medication Errors-Drug #8: Carbamazepine

Medication errors in the pediatric population occur not only in the inpatient setting but also in the outpatient setting. In fact, pediatric medication errors occur in the latter setting at a rate of about 16% of cases.¹

Many potential medication errors may occur. In this series, I focus on 10 errors that are seen frequently in outpatient clinics. In previous articles, I focused on common errors associated with infant acetaminophen,² insulin,³ ceftriaxone,⁴ hydralazine and hydoxzyine,⁵ amoxicillin/clavulanic acid,⁶ ketorolac,⁷ and ciprofloxacin.⁸Medication Error #8: Carbmazepine
A 15-month-old girl (weight, 9 kg) with new-onset generalized tonic-clonic seizure was discharged home from the hospital with a prescription for carbamazepine suspension (45 mg PO bid [10 mg/kg/d]), a medication that the patient had been receiving for a few days in the hospital. A carbamazepine trough obtained during her clinic visit was found to be subtherapeutic (less than 4 μg/mL; goal, 4 to 12 μg/mL). Thus, the dose was increased to 68 mg PO bid (about 15 mg/kg/d).

A week later, the patient was seen again at the clinic and a carbamazepine trough was obtained. The level was once again subtherapeutic. Her parents stated that she was compliant with the medication; no doses were missed.

What’s the problem here?

Discussion
Carbamazepine is an effective medication for managing epilepsy in the pediatric population. This drug comes in various formulations, including immediate-release tablet, extended-release tablet or capsule, and oral suspension.⁹ In this case, the total daily dose was appropriate for this patient, but it should have been divided 4 times a day instead of twice daily.

The absorption and oral bioavailability of carbamazepine suspension are quite variable in the pediatric population. Most pediatric neurologists try to use the tablet formulation and, if possible, dose it twice a day or 3 times a day.¹⁰

Targeting therapeutic concentration with the suspension formulation can sometimes be challenging. This problem does not only occur with carbamazepine; it can also occur with other antiepileptic medications, such as phenytoin.

This error may have been prevented if either the physician or the pharmacist who filled the prescription realized that carbamazepine suspension should be dosed 4 times daily instead of twice a day.

References
1. Kaushal R, Goldmann DA, Keohane CA, et al. Adverse drug events in pediatric outpatients. Ambul Pediatr. 2007;7:383-389.
2. So J. Top 10 common medication errors-and how to avoid them: Drug #1: acetaminophen. September 19, 2011.
3. So J. Top 10 common medication errors-and how to avoid them: Drug #2: insulin. October 18, 2012.
4. So J. Top 10 common medication errors-and how to avoid them: Drug #3: ceftriaxone. November 28, 2012.
5. So J. Top 10 common medication errors-and how to avoid them: Drug #4: hydroxyzine and hydralazine. December 28, 2012.
6. So J. Top 10 common medication errors-and how to avoid them: Drug #5: hydroxyzine and hydralazine. February 1, 2013.
7. So J. Top 10 common medication errors-and how to avoid them: Drug #6: ketorolac. February 27, 2013.
8. So J. Top 10 common medication errors-and how to avoid them: Drug #7: ciprofloxacin. April 2, 2013.
9. Taketomo CK, Hodding JH, Kraus DM. Pediatric Dosage Handbook. 18th ed. Hudson, Ohio: Lexi-Comp; 2011.
10. Gilman JT. Carbamazepine dosing for pediatric seizure disorders: the highs and lows. Ann Pharmacother. 1991;25:1109-1112.