The clinical usefulness of agonist-antagonistic opioid analgesics in chronic pain.

The mixed agonist-antagonist analgesics do not have a major role in the treatment of chronic pain. Pentazocine, the first and most widely used of this group of drugs has two major limitations: by mouth it is not a strong analgesic, but is closer in efficacy to the peripherally acting drugs aspirin and paracetamol than the weak opioids; and its use is associated with psychotomimetic side effects in 10-20 percent of patients. The weak opioid analgesics codeine and dextropropoxyphene are more effective and better tolerated than pentazocine. Buprenorphine is the most useful of the agonist-antagonists in chronic pain patients. It is potent, long-acting (6-9 h) and effective when given sublingually. However, it has a limited effective dose range and produces the same side effects as morphine-like drugs, possibly more frequently at equianalgesic doses. It may be used in the treatment of cancer pain, or in patients with chronic arthritides or other forms of chronic non-cancer pain who require a potent conventional analgesic, as an alternative to the weak opioids or to morphine in low doses. Nalbuphine and butorphanol are only available for parenteral administration which means that their usefulness in the treatment of chronic pain is limited. Meptazinol is restricted by its manufacturers to 'short term' treatment and there is little information on its use in chronic pain patients.