Adjuvants and acute pain – the evidence

Dr Tom Smith,
Consultant in Anaesthetics and Pain Medicine,
Guy's and St Thomas' NHS Foundation Trust.

Biography
I am a consultant in anaesthesia and pain medicine at Guys and St Thomas’ Hospitals, London.  I have worked in Australia, Germany, the USA and the UK.  I have always wished to minimise post-operative pain.  While working in Germany I did an MD thesis looking at the use of local anaesthetic blocks in small children and subsequently I maintained an interest in regional anaesthesia, as well as the use of agents such as gabapentin and ketamine in an effort to provide superior post-operative pain relief.

Abstract
Adjuvants are pharmacological agents added to a drug treatment to increase or aid treatment effect.  For the purpose of this review - and true to the biopsychosocial model that we pain professionals aspire to follow - I will expand the definition to include some non-pharmacological “adjuvants”.  I will not look at the evidence for adding adjuvants to intrathecal/epidural drug mixtures.

A great place to start for any examination of evidence based pain treatments is the Oxford Pain Site “ Bandolier” and its giant brother the Cochrane Database. Here experts gather the data from relevant trials, sift and weight it, before pronouncing considered verdicts.

Anticonvulsants: Bandolier and the Cochrane database say that there is no evidence for benefit of gabapentin or pregabalin in acute pain.  But these reviews are old.  Numerous positive studies have since been published pointing to a worthwhile adjuvant affect of one off pre-op dose of these drugs.  I will look at this new evidence.  Other anticonvulsants cannot be recommended for non-neuropathic acute pain.

Ketamine: A 2006 Cochrane review reported that Ketamine reduces post-operative morphine requirements, reduces PONV with minimal side-effects. Current data could not be translated to a specific treatment regimen.

Steroids: Studies suggest a pre-incisional single dose of dexamethasone reduces post-operative pain not just in oral surgery - but also in gynaecological, orthopaedic surgery and other surgeries.  This has not been the subject of a Cochrane/Bandolier review as yet.

Muscle Relaxants: Cochrane review (2003) reported that muscle relaxants relieved acute low back pain, but warned of a high incidence of CNS adverse events

Antipsychotics: Cochrane review (2008) found evidence for decreased acute pain, but that extrapyramidal side-effects are a concern.

TENS: Cochrane review (2009) reported that studies on TENS in acute pain are not of sufficient quality to analyse.

Acupuncture: A Cochrane review (2003) reported insufficient evidence to comment.

Music: Cochrane review (2009) reported a small reduction in pain (NNT 5) and opioid use (15-20%)

References:

Cochrane Web Site: www.cochrane.org/reviews

Bandolier Web-Site: www.medicine.ox.ac.uk/bandolier