AGONIST/ANTAGONIST ANALGESICS

This group of drugs includes:

• Buprenorphine

• Pentazocine

• Nalbuphine

These are effective analgesics for moderate pain. Buprenorphine has a small place in the management of cancer pain, but the other drugs have no advantages over buprenorphine in this situation, and should be avoided.

Buprenorphine is a strong narcotic, but has a low ceiling effect. It is rapidly metabolized by the liver, and (where available) the sublingual route allows systemic absorption which is almost as potent as by IM injection. About 20% of patients complain of unacceptable nausea or dizziness.

All three drugs have two disadvantages. First, above a certain dose the incidence of side effects increases with no increase in analgesia (the ceiling effect). Second, their high affinity for morphine mu receptors (agonist action) blocks the effect of morphine (antagonist action).

«  Buprenorphine and morphine should never be given together. If buprenorphine is given to a patient on morphine it can displace morphine from the receptor and cause pain (and sometimes withdrawal symptoms of yawning & sweating, rhinorrhea, nausea and restlessness).

The author and publisher have taken precautions to ensure that the information in this book is error-free. However, readers must be guided by their own personal and professional standards of good practice in evaluating and applying recommendations made herein. The contents of this book represent the views and experience of the author, and not necessarily those of the publisher.