Single dose oral diclofenac for postoperative pain

Diclofenac is a benzene-acetic acid derivative that acts, like other NSAIDs, by inhibiting cyclo-oxygenase isoforms that mediate the body's production of the prostaglandins implicated in pain and inflammation. Diclofenac is widely available as a sodium or potassium salt. Diclofenac potassium tablets are known as 'immediate-release' diclofenac as absorption takes place in the gastrointestinal tract whereas 'delayed-release' (enteric-coated) diclofenac tablets resist dissolution until reaching the duodenum. An existing review showed that diclofenac was an effective treatment for acute postoperative pain but did not address the distinction between potassium and sodium salts due to lack of data. The aim of this update is to gather and add appropriate information published subsequently and, data permitting, examine any potential differences between the two different diclofenac formulations.

To assess single dose oral diclofenac for the treatment of acute postoperative pain and determine whether there are differences between the different formulations.

We searched the Cochrane Library (Issue 2, 2003), MEDLINE (1966 to May 1996), EMBASE (1980 to 1996), Biological Abstracts (1985 to 2003), the Oxford Pain Relief Database (1950 to 1994), PubMed (1996 to 2003) and reference lists of articles.

Randomised, double-blind, placebo-controlled clinical trials of single dose, oral diclofenac sodium or diclofenac potassium for acute postoperative pain in adults.

Two reviewers independently assessed trials for inclusion in the review, quality and extracted data. The area under the pain relief versus time curve was used to derive the proportion of patients prescribed diclofenac or placebo with at least 50% pain relief over four to six hours using validated equations. The number needed to treat (NNT) was calculated. Information on adverse effects was also collected.

One additional trial was included and added to the six trials included in the original review. All seven trials provided data for quantitative analysis: 581 patients were treated with diclofenac and 364 were treated with placebo. The NNT for at least 50% relief over four to six hours with diclofenac 25 mg, 50 mg and 100 mg compared with placebo was 2.8 (95% CI 2.1 to 4.3), 2.3 (2.0 to 2.7) and 1.9 (1.6 to 2.2) respectively. Though higher doses produced lower (better) NNTs, statistical significance was not achieved. There was no significant difference between diclofenac 50 mg and placebo in the proportion of patients experiencing dizziness, headache, nausea or vomiting. The weighted median duration of analgesia was 2 hours for placebo, 6.7 hours for diclofenac 50 mg and 7.2 hours for diclofenac 100 mg. Sensitivity analyses for drug formulation, pain model, trial size and quality did not reveal any statistically significant differences.

Oral diclofenac is an effective single-dose treatment for moderate to severe postoperative pain. There was no significant difference between diclofenac and placebo in the incidence of adverse effects, or between diclofenac sodium and potassium, different pain models, smaller and larger trials and trials of higher and lower quality.