الوصف
Carbamazepine induces hepatic CYP enzymes involved in thyroid hormone metabolism, increasing levothyroxine clearance and potentially causing hypothyroid relapse in patients on replacement therapy.
الآلية
CYP3A4 and UGT induction by carbamazepine increases hepatic glucuronidation and oxidative metabolism of T4, raising levothyroxine requirements; TSH rises as free T4 levels fall.
الأهمية السريرية
Multiple studies confirm that carbamazepine reduces free T4 concentrations and raises TSH in hypothyroid patients on stable levothyroxine therapy, often requiring 20–30% dose increases.
التدبير
Monitor thyroid function tests 4–6 weeks after starting or dose-escalating carbamazepine; anticipate levothyroxine dose increases; conversely, reduce levothyroxine if carbamazepine is withdrawn.