Single dose oral mefenamic acid for acute postoperative pain in adults Stable (no update expected for reasons given in 'What's new')

Abstract

Abstract Background

Mefenamic acid is a non‐steroidal anti‐inflammatory drug (NSAID). It is most often used for treating pain of dysmenorrhoea in the short term (seven days or less), as well as mild to moderate pain including headache, dental pain, postoperative and postpartum pain. It is widely available in many countries worldwide.

Objectives

To assess the efficacy of single dose oral mefenamic acid in acute postoperative pain, and any associated adverse events.

Search methods

We searched Cochrane CENTRAL, MEDLINE, EMBASE and the Oxford Pain Relief Database for studies to December 2010.

Selection criteria

Single oral dose, randomised, double‐blind, placebo‐controlled trials of mefenamic acid for relief of established moderate to severe postoperative pain in adults.

Data collection and analysis

Studies were assessed for methodological quality and the data extracted by two review authors independently. Summed total pain relief (TOTPAR) or pain intensity difference (SPID) over 4 to 6 hours was used to calculate the number of participants achieving at least 50% pain relief. These derived results were used to calculate, with 95% confidence intervals, the relative benefit compared to placebo, and the number needed to treat (NNT) for one participant to experience at least 50% pain relief over 4 to 6 hours. Numbers of participants using rescue medication over specified time periods, and time to use of rescue medication, were sought as additional measures of efficacy. Information on adverse events and withdrawals was collected.

Main results

Four studies with 842 participants met the inclusion criteria; 126 participants were treated with mefenamic acid 500 mg, 67 with mefenamic acid 250 mg, 197 with placebo, and 452 with lignocaine, aspirin, zomepirac or nimesulide. Participants had pain following third molar extraction, episiotomy and orthopaedic surgery. The NNT for at least 50% pain relief over 6 hours with a single dose of mefenamic acid 500 mg compared to placebo was 4.0 (2.7 to 7.1), and the NNT to prevent use of rescue medication over 6 hours was 6.5 (3.6 to 29). There were insufficient data to analyse other doses or active comparators, or numbers of participants experiencing any adverse events. No serious adverse events or adverse event withdrawals were reported in these studies.

Authors' conclusions

Oral mefenamic acid 500 mg was effective at treating moderate to severe acute postoperative pain, based on limited data. Efficacy of other doses, and safety and tolerability could not be assessed.

Author(s)

Rachel Moll, Sheena Derry, R Andrew Moore, Henry J McQuay

Abstract

Plain language summary

Single dose oral mefenamic acid for acute postoperative pain in adults

Mefenamic acid is a non‐steroidal anti‐inflammatory drug (NSAID) that is used as a painkiller (analgesic). Four studies involving a total of 842 participants were included in this review. Because fewer than 200 participants were treated with mefenamic acid within these four studies, results must be treated with caution. A good level of pain relief is experienced by almost half (48%) of those with moderate to severe postoperative pain after a single dose of mefenamic acid 500 mg, compared to about 20% with placebo, and fewer will need additional analgesia within 6 hours (47% versus 62%). This level of pain relief is comparable to that experienced with paracetamol 1000 mg. Adverse events could not be assessed in these studies.

Author(s)

Rachel Moll, Sheena Derry, R Andrew Moore, Henry J McQuay

Reviewer's Conclusions

Authors' conclusions

Implications for practice

Mefenamic acid 500 mg is likely to be an effective analgesic, but there is insufficient evidence from this limited data set to give a reliable estimate of the size of its effect. No serious adverse events were reported in any of the studies, though numbers were too small to exclude rare but serious harm.

Implications for research

Given the large number of available drugs of this and similar classes to treat postoperative pain, there is no urgent research agenda. More studies could more accurately determine efficacy, but are unlikely to be performed because of well known alternatives. Such studies would need to improve reporting of outcomes other than pain relief and pain intensity difference, such as adverse events and time to remedication. 

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