Which of the following medications is NOT affected by the MDR1 mutation?

The medication that is not affected by the MDR1 mutation is penicillin. The MDR1 gene encodes for P-glycoprotein, a membrane transporter that plays a critical role in drug absorption, distribution, and excretion. This mutation is particularly relevant in certain dog breeds, such as Collies, where it can result in severe adverse reactions to medications that are substrates of P-glycoprotein.

Penicillin, an antibiotic used to treat bacterial infections, does not rely on P-glycoprotein for its pharmacokinetics. It is primarily eliminated through the kidneys and does not accumulate in the central nervous system, making it safe for use in dogs with MDR1 mutations. This contrasts with the other drugs mentioned, which are influenced by the MDR1 gene. For instance, milbemycin, doxorubicin, and acepromazine can be harmful to dogs with this mutation since their proper absorption and toxicities can be notably affected, leading to potential serious side effects.

Understanding the implications of the MDR1 mutation is crucial for veterinary technicians when prescribing medications, to ensure the safety and well-being of sensitive breeds.