TRYING alternative analgesics for pain relief until an effective one is found is impractical as pain specialists tend not to “flip-flop” between drugs of the same class, says an Australian pain expert.

Associate Professor Pam Macintyre, director of the acute pain service at Royal Adelaide Hospital, was commenting on the review of single-dose oral analgesics for acute postoperative pain in adults, published in the latest edition of The Cochrane Library. (1)

The review authors said commonly used analgesic drugs at the recommended or licensed doses produced good pain relief in some, but not all, patients with pain. They suggested that doctors should find alternative analgesic drugs or procedures that do work for their patients.

Dr Macintyre said anaesthetists usually did not switch between drugs of the same class in an attempt to improve pain relief. For example, they would add a non-steroidal anti-inflammatory drug (NSAID) to paracetamol and, if that was not effective, they would not change the NSAID but add an opioid.

“And if an opioid was not working we would try increasing the dose as there is no evidence that one works better than another”, she said.

Single dose studies were not very helpful and the review was simply a guide for comparison of numbers needed to treat (NNT) for 50% or more pain relief over 4 to 6 hours compared to placebo, Dr Macintyre said.

The review included 35 Cochrane reviews of randomised trials of the analgesic efficacy of individual drug interventions in acute postoperative pain, with results from about 45 000 patients in about 350 individual studies. It found reliable results for 46 drug-dose combinations in all painful postoperative conditions, 45 in dental pain and 14 in other painful conditions such as orthopaedic and abdominal surgery. It also identified drugs for which there were unreliable, inadequate or no data.

“Not all participants had good pain relief and for many drug/dose combinations 50% or more did not achieve at least 50% maximum pain relief over 4 to 6 hours”, the authors said.

Dr Macintyre said the review included very little data on opioid medications. The NNT for opioids was debatable because they should be titrated for each patient and there were huge inter-individual variations in requirements for pain relief.

But there was some useful information in the review, such as the fact that the combination of dextropropoxyphene and paracetamol is not better than paracetamol alone, she said.

Professor Stephan Schug, director of pain medicine at Royal Perth Hospital, said the review was a very pure and scientifically clean summary of many excellent meta-analyses but it did not reflect clinical reality.

“It is uncommon to use single doses of a drug to treat acute pain; patients are not always as healthy as the patients in these studies, and most pain is treated by combinations of analgesics which are not studied, with the exception of a few”, he said.

The review was of limited value for postoperative pain control in general because many patients would not be able to take oral medications immediately after surgery.

“However, it is of help for treating all types of painful conditions where patients usually take painkilling tablets, for example, toothache or pain after outpatient surgery”, he said.

“Opioids and aspirin showed some adverse effects and this information and consideration of comorbidities might influence choice of analgesic more than assumed efficacy in a specific patient”, Professor Schug said.

– Cathy Saunders

1. Cochrane Database of Systematic Reviews 2011; issue 9

Posted 12 September 2011

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