Single dose dihydrocodeine for acute postoperative pain

Dihydrocodeine is a synthetic opioid analgesic developed in the early 1900s. Its structure and pharmacokinetics are similar to that of codeine and it is used for the treatment of postoperative pain or as an antitussive. It is becoming increasingly important to assess the relative efficacy and harm caused by different treatments. Relative efficacy can be determined when an analgesic is compared with control under similar clinical circumstances.

To quantitatively assess the analgesic efficacy and adverse effects of single-dose dihydrocodeine compared with placebo in randomised trials in moderate to severe postoperative pain.

Published reports were identified from a variety of electronic databases including Medline, Biological Abstracts, Embase, the Cochrane Library and the Oxford Pain Relief Database. Additional studies were identified from the reference lists of retrieved reports.

The following inclusion criteria were used: full journal publication, clinical trial, random allocation of patients to treatment groups, double blind design, adult patients, pain of moderate to severe intensity at baseline, postoperative administration of study drugs, treatment arms which included dihydrocodeine and placebo and either oral or injected (intramuscular or intravenous) administration of study drugs.

Data collection and analysis: Summed pain intensity and pain relief data over 4-6 hours were extracted and converted into dichotomous information to yield the number of patients obtaining at least 50% pain relief. This was used to calculate relative benefit and number-needed-to-treat for one patient to obtain at least 50% pain relief. Single-dose adverse effect data were collected and used to calculate relative risk and number-needed-to-harm.

Fifty-two reports were identified as possible randomised trials which assessed dihydrocodeine in postoperative pain. Four reports met the inclusion criteria; all assessed oral dihydrocodeine. Three reports (194 patients) compared dihydrocodeine with placebo and one (120 patients) compared dihydrocodeine (30 mg or 60 mg) with ibuprofen 400 mg. For a single dose of dihydrocodeine 30 mg in moderate to severe postoperative pain the NNT for at least 50% pain relief was 8.1 (95% confidence interval 4.1 to 540) when compared with placebo over a period of 4-6 hours. Pooled data showed significantly more patients to have reported adverse effects with dihydrocodeine 30 mg than with placebo. When compared to ibuprofen 400 mg both dihydrocodeine 30 mg and 60 mg were significantly inferior.

A single 30 mg dose of dihydrocodeine is not sufficient to provide adequate pain relief in postoperative pain. Statistical superiority of ibuprofen 400 mg over dihydrocodeine (30 mg or 60 mg) was shown.