What opioid analgesic (pain reliever) causes the least pruritus (itchiness)?

From the Guidelines

Buprenorphine is the opioid analgesic that causes the least itchiness among commonly used options, due to its unique mechanism of action as a partial opioid agonist with a high binding affinity for the μ-opioid receptor. When itching is a concern, buprenorphine would be preferred over other opioids such as morphine, hydromorphone, or codeine, which are more likely to cause pruritus 1. The typical dosing for buprenorphine depends on the formulation - for chronic pain, a transdermal patch is approved and can provide analgesia over a long period of time, with doses ranging from 5-20 mcg/hour 1.

Some key points to consider when using buprenorphine for pain management include:

• Buprenorphine has a ceiling effect on respiratory depression, making it a safer option for patients with respiratory concerns 1
• The transdermal patch formulation bypasses hepatic metabolism, providing better analgesia relative to the sublingual formulation 1
• Buprenorphine can be used in combination with other opioids, such as fentanyl or hydromorphone, for acute pain management 1
• If itching does occur with buprenorphine or other opioids, it can be managed with antihistamines like diphenhydramine or low-dose naloxone 1

It's worth noting that buprenorphine has proven efficacy and may be safer than full opioid agonists in the treatment of chronic pain, with fewer adverse events compared to transdermal fentanyl and morphine 1. Overall, buprenorphine is a good option for patients who experience itching with other opioids, due to its unique mechanism of action and favorable side effect profile.

From the Research

Opioid Analgesia and Itchiness

• Opioid administration can cause pruritus, which is an unpleasant and irritating sensation of the skin that provokes an urge to scratch or rub 2.
• The incidence of opioid-induced pruritus differs with different opioids and routes of administration, and the various mechanisms can be broadly divided into peripheral and central 2.
• Fentanyl is known to have a relatively small effect on peripheral vascular resistance compared to morphine, and it does not cause a significant increase in plasma histamine levels 3.

Comparison of Opioids

• Morphine produces peripheral vasodilation and frequently significant hypotension due to the release of histamine, whereas fentanyl does not have this effect 3.
• Fentanyl-like opioids do not affect currents through the 5-HT(3A) receptor significantly in the clinically relevant nanomolar concentration range, whereas hydromorphone is more potent and slows the current activation- and desensitization-kinetics significantly 4.
• The rank order of opioid potencies for human 5-HT(3A) receptors is opposite of that for opioid receptors, suggesting a specific interaction with 5-HT(3A) receptors for morphine and hydromorphone 4.

Opioid-Induced Pruritus Treatment

• Opioid receptor antagonists and mixed agonist and antagonists, especially μ-opioid antagonists and κ-opioid agonists, are effective in relieving opioid-induced pruritus 2, 5.
• A multimodal analgesic treatment regimen combined with a mixed antagonist and κ agonists, especially μ-opioid antagonists, and κ-opioid agonists, seems to be the current best treatment modality for the management of opioid-induced pruritus and pain 2.