A patient taking phenytoin for seizures is newly prescribed enteral tube feeds. Which pharmacokinetic interaction is the technician most likely to hear the pharmacist discussing?
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AEnteral feeds increase phenytoin bioavailability by stimulating CYP2C9 induction
BPhenytoin chelates calcium in the feed, causing severe hypocalcemia
CEnteral feeds significantly decrease phenytoin absorption, requiring the feeds to be held around dose times and serum levels to be monitored
DEnteral feeds have no documented interaction with phenytoin
✓ Correct answer: C. Enteral feeds significantly decrease phenytoin absorption, requiring the feeds to be held around dose times and serum levels to be monitoredContinuous enteral nutrition reduces phenytoin oral bioavailability substantially (mechanism not fully elucidated, possibly protein binding or adsorption to the feeding tube); standard practice is to hold feeds 1–2 hours before and after phenytoin doses and monitor drug levels closely.
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