Lesson 4 of 5 · 26 min

Carbamazepine: Induction, HLA-B*1502 & Blood Counts

Learning objectives

Describe autoinduction and CYP3A4 induction
Identify who needs HLA-B*1502 screening
Monitor for agranulocytosis and hyponatremia

Carbamazepine (extended-release formulation) is used for acute mania and mixed episodes. It is a potent inducer of CYP3A4 and induces its own metabolism (autoinduction) over the first several weeks.

Boxed warnings include serious dermatologic reactions strongly associated with HLA-B*1502 (more common in some Asian ancestries — screening is recommended before starting in at-risk patients), and aplastic anemia/agranulocytosis.

It can cause SIADH-like hyponatremia. As an inducer, it lowers levels of many drugs, including hormonal contraceptives, making them less effective.

Key points

Strong CYP3A4 inducer + autoinduction
Screen HLA-B*1502 in at-risk ancestry
Monitor CBC, sodium, LFTs

Exam pearls

◆ Carbamazepine makes oral contraceptives LESS effective
◆ Fever, sore throat, bruising → check CBC
◆ Hyponatremia: confusion, headache, nausea

Educational content for exam preparation; verify dosing and monitoring with current prescribing information. References: [APA 7 placeholder — to be supplied by author].

Lesson check

Question 1 · carbamazepine

Before starting carbamazepine in a patient of Han Chinese ancestry, which test is recommended?

Question 2 · carbamazepine

A patient on oral contraceptives starts carbamazepine. What is the MOST important counseling point?