Oxford league table of analgesics in acute pain

This league table was constructed for analgesics in acute pain. Information was from systematic reviews of randomised, double-blind, single-dose studies in patients with moderate to severe pain. For each review the outcome was identical – that is at least 50% pain relief over 4-6 hours. The pain measurements were standardised, and have been validated.

The league table works because it only has apples, and is not a fruit salad. Only like is compared with like, and there is a common comparator throughout, namely placebo. Information is presented in a number of formats, but the definitive source is the full Table , which has the number of patients in the comparison, the percent with at least 50% pain relief with analgesic, the number-needed-to-treat (NNT) and the high and low 95% confidence interval. This Table will be updated as more information becomes available. PDF versions of the FULL league table and of the TRUNCATED version are available following updating in 2007. There is also a listing for oral COMBINATION analgesics.

Much of the information is about drugs or doses not commonly used, and which is therefore of academic interest only. Figure 1 shows the NNTs for a number of common drugs and doses. The details are in Table 1, with links to the full reviews.

Figure 1: 2007 League table of number needed to treat (NNT) for at least 50% pain relief over 4-6 hours in patients with moderate to severe pain, all oral analgesics except IM morphine

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Effective relief can be achieved with oral non-opioids and non-steroidal anti-inflammatory drugs. Analgesic efficacy is expressed as the NNT, the number of patients who need to receive the active drug for one to achieve at least 50% relief of pain compared with placebo over a 4-6 hour treatment period. The most effective drugs have a low NNT of just over 2. This means that for every two patients who receive the drug one patient will get at least 50% relief because of the treatment (the other patient may or may not obtain relief but it does not reach the 50% level).

The NNT is treatment-specific, which is useful for comparison of relative efficacy. Because these NNT comparisons are against placebo, the best NNT of 2 means that 50 of 100 patients will get at least 50% relief specifically because of the treatment. Another twenty will have a placebo response giving them at least 50% relief. With ibuprofen 400 mg, therefore, about 70 of 100 in total will have effective pain relief. For comparison, with 10 mg intramuscular morphine about 53% of patients get more than 50% pain relief. Because the effect of placebo is added in, the comparisons between analgesics are not as stark as with NNT.

It is clear that the oral NSAIDs do extremely well in this single-dose postoperative comparison. At these doses they all have NNT values of between 2 and 3, and the point estimate of the mean is below that of (i.e. better than) 10 mg of intramuscular morphine, even though the confidence intervals overlap. The simple analgesics, aspirin and paracetamol are significantly less effective than 10 mg intramuscular morphine. The point estimates of the NNT are higher, and there is no overlap of the confidence intervals. Weak opioids perform poorly in single doses on their own. Combining them with simple analgesics improves analgesic efficacy.

Drawbacks of the league table

The most important drawback is size. Small trials (or small data sets) cannot accurately estimate the magnitude of the analgesic effect. To know that the NNT of an analgesic is 3.0 with a confidence interval of 2.5 to 3.5 we need almost 1000 patients in a comparative trial. So as you contemplate the numbers, be conscious of the amount of information upon which NNTs and percent of patients with at least 50% pain relief are based. In practice any comparison with more than 250 or so patients is probably adequate.

For instance, ibuprofen 800 mg is at the top of the league, with an NNT of 1.6 and with 100% of patients achieving at least 50% pain relief. But only 76 patients have ever been involved in comparative trials with placebo. This makes the apparent wonderful result less so, and you should treat it cautiously.

The information is presented here, warts and all, so that professionals and public can make their own assessments.

What is missing?

Adverse effects from single-dose analgesic trials are rarely helpful with simple analgesics and NSAIDs, though they may be much more helpful with opioids. Work on adverse effects is being done, and a summary of this will appear on this site later in 1999.

Some analgesics used commonly outside the UK may not be represented. Again work is ongoing to plug these gaps, but so often the randomised trials (placebo-controlled, randomised, double-blind and with proper outcome measures and entry criteria), have not been done.

Finally cost information is not given here, because it can vary so much throughout the world.

This page used to be available at https://www.medsci.ox.ac.uk/ but now gives error 404. Reproduced here because the information remains useful.