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Evidence-based Analgesic League Table

Abstract of a paper for
1st Pan African Congress on Pain
Alexandria 9-11 November
(see meetings sections)

Geoff Gourlay
Pain Management Unit, Flinders Medical Centre, Bedford Park, South Australia, AUSTRALIA 5042

Physicians are inundated with information and data from a vast variety of sources regarding the diagnosis and treatment of the myriad of conditions and diseases for which patients visit their doctor. In the areas of the drug treatment of acute, chronic and cancer pain, like many other areas of pharmacotherapy, this information has differing degrees of accuracy and reliability. The gold standard study design to establish the efficacy of a particular drug relative to placebo or other active control continues to be the randomised, controlled, double blind study (RCT’s). Historically, such studies were undertaken in Hospital and University Departments and usually involved small patient numbers; yet we continue to make important population based predictions from these studies. In more recent times, large multi-centred trials in various countries (often sponsored by pharmaceutical companies) recruited significantly greater patient numbers thereby hopeftilly providing greater reliability in the extrapolation of results to the population at large. The alternative approach is meta-analysis or systematic reviews, which involves combining the results of similar studies using the same drug where particular attention is given to study selection on the basis of methodology and outcome measures. Frequently, systematic reviews fail to provide useftil recommendations because of the poor quality of the primary studies.

Studies from the Pain Relief Unit in Oxford have undertaken a number of systematic reviews of various opioids and NSATD’s in acute pain control (both post-operative pain and dental pain models) as well as the efficacy on antidepressants, anticonvulsants and other therapies in chronic pain. In the majority of these studies, the outcome measure is the Number Needed to Treat (NNT) for at least 50% pain relief. For example, a single 10 mg IM morphine injection for acute pain control has a NNT of 2.9 - i.e. 1 in 2.9 patients with moderate to severe pain obtained the outcome of 50% pain relief, who would not have done so if administered placebo. This approach has confirmed dose response relationships for different doses of the same drug. For acute pain, these reviews indicate, inter alia, the following; (1) the first dose of opioid provides poor pain relief (already known), (2) NSAID’s frequently provide equivalent or superior pain relief than opioids (diclofenac 50mg, NNT = 2.3), (3) codeine alone or in combinations provides poor pain relief (codeine 60mg, NNT = 16.7) and (4) topical NSAID’s are effective in acute (and chronic) pain.

For chronic neuropathic pain (trigeminal neuralgia, diabetic neuropathy), anticonvulsants and antidepressants have similar NNT’s for pain relief, minor and major side effects (the equivalent term is NNH or Numbers Needed to Harm).

See also:

Pharmacokinetics of opioids
New perspectives on the oldest drug

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