Which of the following medications is affected by MDR1 mutation?

The correct choice is acepromazine, a medication that is indeed affected by the MDR1 (Multi-Drug Resistance 1) mutation. The MDR1 gene encodes for P-glycoprotein, a critical component in the blood-brain barrier that helps to export certain drugs out of the brain and other tissues. When there is a mutation in the MDR1 gene, this transport mechanism is compromised, which can lead to increased toxicity when certain drugs are administered.

Acepromazine, an antipsychotic and tranquilizer commonly used in veterinary medicine, can accumulate in the central nervous system in animals with the MDR1 mutation. This increased accumulation can lead to adverse effects or even overdose, particularly in breeds such as Collies and related herding breeds that are known to have this mutation.

In contrast, ibuprofen, dexamethasone, and fentanyl do not have their pharmacological effects significantly influenced by the MDR1 mutation. Ibuprofen is a nonsteroidal anti-inflammatory drug, dexamethasone is a corticosteroid, and fentanyl is an opioid analgesic. These medications typically do not interact with P-glycoprotein in the same way, making them less affected by changes in the MDR1