A nurse is reviewing the orders of a newly admitted client who has a prescription for a fentanyl transdermal patch for severe pain. Which new prescription should the nurse be concerned about causing a serious drug-drug interaction?

A. Levothyroxine 125 mcg once daily: Levothyroxine does not have significant interactions with fentanyl. Co-administration does not increase the risk of respiratory depression or sedation and is generally safe in pain management contexts. B. Ibuprofen 400 mg PO every 6 hours PRN: NSAIDs like ibuprofen can be safely used alongside fentanyl for additional analgesia. There is no significant pharmacologic interaction that would increase the risk of severe adverse effects such as respiratory depression. C. Lorazepam 1 mg PO every 8 hours PRN: Both fentanyl and lorazepam are central nervous system (CNS) depressants. Concurrent use can lead to additive effects, significantly increasing the risk of respiratory depression, profound sedation, hypotension, and even death, making this combination particularly concerning. D. Penicillin 500 mg IV every 8 hours: Penicillin does not interact with fentanyl in a way that would enhance CNS depression or cause serious adverse effects. Co-administration is generally considered safe.