Описание
Valproic acid displaces phenytoin from protein binding and inhibits its metabolism, leading to increased free phenytoin levels despite total levels that may appear unchanged or decreased.
Механизм
Valproate displaces phenytoin from albumin (protein binding competition) and inhibits its CYP2C9-mediated metabolism; free phenytoin fraction increases.
Клиническое значение
Standard total phenytoin levels may be misleadingly normal while free levels are toxic; nystagmus, ataxia, and mental status changes may develop.
Тактика ведения
Monitor free (unbound) phenytoin levels rather than total levels; watch for phenytoin toxicity signs and adjust dose accordingly.
Медицинский отказ от ответственности
This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making medication decisions.