I frequently work with patients and caregivers who are managing patients at the end of life and in hospice-type situations. Knowing and understanding differences between common opioids is critical to my work as a clinical pharmacist. In this article, I’ll discuss a comparison of morphine versus oxycodone.
Morphine Versus Oxycodone – Dosage Forms
Dosage form flexibility is important in geriatric and hospice in general. One advantage of morphine is that it has a ton of different dosage forms compared to oxycodone. Oxycodone can only be given orally (United States) which may be an issue in some patients. The most commonly used dosage form with oxycodone is tablets, but there is an oral solution as well. Morphine has a variety of dosage forms which allows for easier administration regardless of the clinical situation. Morphine dosage forms include oral, rectal, and injectable. With a variety of dosage forms, comes great responsibility. Recall a previous post where I discussed understanding the differences between various morphine strengths.
Renal Function
Renal function is important to think about with both medications. The issue with morphine in renal impairment has been much more publicized than oxycodone. Specifically with morphine, it has metabolites that can accumulate. Morphine-3-glucuronide has been reported to lower seizure threshold and morphine-6-glucuronide has been associated with opioid effects. Accumulation of both can lead to potential toxicities. Patient monitoring and possibly taking a more conservative approach for both oxycodone and morphine may be warranted in patients with poor renal function.
Morphine Versus Oxycodone – CYP Enzymes
A unique characteristic of morphine is that it avoids the CYP enzymes as a major breakdown pathway. Oxycodone differs in that it is altered by CYP2D6 and CYP3A4. This could lead to variable results based upon pharmacogenomic alterations as well as drug interactions. In patients who are non-responders to oxycodone or very sensitive to its effects, the reason for this may lie in the activity related to these two enzymes. CYP3A4 inhibitors would be likely to increase the action of oxycodone while inducers would be likely to reduce the activity of the drug. Morphine would be unaffected.
Antiplatelet Agents Interaction
Morphine has been reported to affect antiplatelet agents. More specifically, there is some data that demonstrates its potential to impair the effects of P2Y12 inhibitors such as clopidogrel. I’m not aware of any evidence of oxycodone causing this issue. This is something to consider when selecting agents in patients taking P2Y12 inhibitors.
Morphine Versus Oxycodone – Potency
In general, oxycodone is considered to be slightly more potent than morphine. In an ORAL to ORAL comparison of these agents, 15 mg of morphine is approximately equivalent to 10 mg of oxycodone. You MUST remember that these equivalencies are not exact and can vary from patient to patient. I’ve discussed opioid equivalencies in greater detail in this previous post (Youtube Video included).
What other differences between morphine and oxycodone are important in your practice?
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