Central Institute of Psychiatry - 9 July 2022
Pharmacology
Medium
A patient is taking carbamazepine, which of the following lab finding is suggestive of a side effect of carbamazepine?
Appeared in: Central Institute of Psychiatry - 9 July 2022
Explanation
- Carbamazepine has a well-documented risk of causing bone marrow suppression, which can be a serious and life-threatening adverse effect.
- This suppression manifests as a decrease in blood cell production, leading to leukopenia (low white blood cell count), thrombocytopenia (low platelets), or aplastic anemia.
- A WBC count of 3,000/cu mm is below the normal range (typically 4,000-11,000/cu mm) and is a clear indicator of leukopenia, a direct side effect of the drug.
- This finding is clinically significant as it places the patient at a high risk for developing infections.
Why Other Options Were Wrong
- Option A: A sodium level of 140 mEq/L is within the normal range of 135-145 mEq/L.
- Option B: A Blood Urea Nitrogen (BUN) level of 10 mg/dl is within the normal range of 7-20 mg/dL, indicating adequate kidney function.
- Option D: A creatinine level of 3.5 mg/dl is significantly elevated (normal range is approx. 0.6-1.3 mg/dL) and indicates renal impairment. However, severe renal failure is not a common or characteristic adverse effect of carbamazepine.
Related Visual
Clinical Relevance
- Nursing practice connection: Use the key finding related to Adverse effects of carbamazepine and lab value interpretation to guide bedside assessment, documentation, and the next nursing action.
- Nurses must monitor the complete blood count (CBC) before initiating and periodically during carbamazepine therapy to detect bone marrow suppression early.
- Patient education is crucial. Instruct patients to immediately report any signs of infection (fever, sore throat, chills) or bleeding (petechiae, bruising, bleeding gums), as these can be early indicators of hematologic toxicity.
- What if? If the patient's lab results showed a sodium level of 128 mEq/L instead, that would also be a correct answer, as hyponatremia is another well-known adverse effect of carbamazepine.
How to Approach the Question
- First, identify the key elements of the question: the drug is carbamazepine, and you need to find a lab value that represents a side effect.
- Second, recall the major adverse effects associated with carbamazepine. The most critical ones to remember are bone marrow suppression (leading to low blood counts like leukopenia) and hyponatremia (low sodium).
- Third, systematically evaluate each lab value in the options against its normal range.
- Compare the abnormal findings to the known side effect profile of carbamazepine. A WBC count of 3,000/cu mm is low (leukopenia) and directly matches a known serious side effect.
- Eliminate the other options. The sodium and BUN levels are normal. The creatinine is high, but this is not a classic side effect of carbamazepine, making the low WBC the most direct and expected adverse reaction among the choices.
Concept Tested & Keywords
- Concept Tested: Adverse effects of carbamazepine and lab value interpretation.
- Stem keywords: carbamazepine, lab finding, side effect
- Lead-in keywords: suggestive of
- Negative lead-in flag: false
Question ID
QInEkJUjyWCnQ6Mh9oJES1
Reference Book
E6 Kaplan Sadock's Synopsis of Psychiatry-2022 (pp 1-3768 of 3768) pp. 2092-2094, 2086-2088
E6 Robert Boland, Marcia L. Verduin - Kaplan and Sadock's Comprehensive Text of Psychiatry-Wolters Kluwer Health (2024) (pp 1-16525 of 16525) p. 10670-10672
Practise the full Central Institute of Psychiatry - 9 July 2022
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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