The use of pentazocine as a strong analgesic in urological practice

Opioid agonist-antagonist drugs in acute and chronic pain states

The agonist-antagonist opioid analgesics are a heterogeneous group of drugs with moderate to strong analgesic activity comparable to that of the pure agonist opioids such as codeine and morphine but with a limited effective dose range. The group includes drugs which act as an agonist or partial agonist at one receptor and an antagonist at another (pentazocine, butorphanol, nalbuphine, dezocine) and drugs acting as a partial agonist at a single receptor (buprenorphine). These drugs can be classified as nalorphine-like or morphine-like. Meptazinol does not fit into either classification and occupies a separate category. Pentazocine, butorphanol and nalbuphine are weak mu-antagonists and kappa-partial-agonists. All three drugs are strong analgesics when given by injection: pentazocine is one-sixth to one-third as potent as morphine, nalbuphine is slightly less potent than morphine, and butorphanol is 3.5 to 7 times as potent. The duration of analgesia is similar to that of morphine (3 to 4 hours). Oral pentazocine is closer in analgesic efficacy to aspirin and paracetamol (acetaminophen) than the weak opioid analgesics such as codeine. Neither nalbuphine nor butorphanol is available as an oral formulation. At usual therapeutic doses nalbuphine and butorphanol have respiratory depressant effects equivalent to that of morphine (though the duration of such effects with butorphanol may be longer). Unlike morphine there appears to be a ceiling to both the respiratory depression and the analgesic action. All of these 3 drugs have a lower abuse potential than the pure agonist opioid analgesics such as morphine. However, all have been subject to abuse and misuse, and pentazocine (but not the others) is subject to Controlled Drug restrictions. Buprenorphine is a potent partial agonist at the mu-receptor, and by intramuscular injection is 30 times as potent as morphine. A ceiling to the analgesic effect of buprenorphine has been demonstrated in animals and it is also claimed in humans. However, there are no reliable data available to define the maximal dose of buprenorphine in humans. A practical ceiling exists for sublingual use in that the only available formulation is a 2 micrograms tablet and few patients will accept more than 3 or 4 of these in a single dose. The duration of analgesia is longer than that of morphine, at 6 to 9 hours. There have been suggestions that buprenorphine causes less respiratory depression than morphine, but viewed overall it appears that in equianalgesic doses the 2 drugs have similar respiratory depressant effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Pentazocine

Published clinical studies and extensive experience has shown that pentazocine, the first of the practical agonist/antagonist analgesics, is a potent analgesic with wide application in clinical medicine. It has been shown to have a spectrum of pharmacological activity which has qualitative differences from pure opiate agonists and these have important implications in clinical medicine. Pentazocine can provide analgesia as great as the opiates including morphine and meperidine, but does not have the same effect on mood. It is, therefore, less effective than the opiates in those situations where an anxiolytic effect is desired. Conversely, it produces less CNS depression in particular with regard to respiratory depression and nausea and vomiting. It also does not have the same potential for producing hypotension. The parenteral administration of pentazocine produces rapid strong analgesia which is of less duration than with morphine or meperidine. The oral administration of pentazocine is less predictable with regard to response but in appropriate patients it is capable of providing a similar degree of analgesia to that achieved with parenteral pentazocine. The dependence liability of pentazocine is substantially less than that with the opiates, and where abuse of parenteral pentazocine alone has taken place, it has usually been in medical and paramedical personnel seeking a support for inadequate personalities. Though physical and psychic dependence to parenteral pentazocine is undoubtedly possible, its incidence is extremely low with regard to the extent of the therapeutic use of pentazocine.