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Decreased responsiveness to oxycodone: A case of a pharmacokinetic drug interaction?
Doreen Pon1, Joon Hwang2, Teresa Lo2
1Assistant Professor, Department of Pharmacy Practice and Administration, College of Pharmacy, Western University of Health Sciences, Pomona, California; Faculty in Residence, Department of Pharmacy, City of Hope National Medical Center, Duarte, California.
Abstract:
Concurrent administration of oxycodone and phenytoin may cause, through induction of CYP3A4 enzymes, decreased analgesic effects of oxycodone. However, no descriptions of this interaction exist. A patient who was on oxycodone for chronic back pain was admitted to the hospital. Five days after initiating fosphenytoin, the patient experienced a dramatic escalation in his pain and lack of response to oxycodone breakthrough doses. Changing oxycodone to hydromorphone resulted in significantly improved analgesia. Concurrent use of fosphenytoin and oxycodone may increase the conversion of oxycodone to inactive metabolites, resulting in decreased analgesia. This may be avoided using hydromorphone, morphine, or oxymorphone.
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