Shaky Evidence Supporting Amitriptyline For Neuropathy

Today's post from cochrane.org (see link below) looks at the evidence supporting the use of amitriptyline as a treatment for neuropathic pain and as many other serious investigations in the past have done; has found that the drug is of very little benefit to neuropathy sufferers. Or at least, there's just not enough research and evidence to prove otherwise. Yet it is drug number one on the lists of standard treatments for nerve pain...why? It's more of a 'following the logic' sort of reasoning; you begin small and build up. Basically that predicts a trajectory ending with opiates but is of little benefit to patients. Apart from the associated side effects of taking anti-depressants, amitriptyline has not been proved to be of any significant benefit in reducing neuropathy symptoms, yet doctors routinely begin with it, in the hope that what they see as, only a very mild drug, will be enough to quell the symptoms. It's been the standard start-up drug of choice for decades; isn't it about time that the industry looked at the evidence and stopped putting us at risk from unnecessary side effects? The evidence suggests that other drugs are far better for the task but unfortunately we still have to go through the hope and ultimate failure of amitriptyline before any relief can be found by moving on to more effective treatments.
 

Amitriptyline for neuropathic pain in adults  
Published: 1 August 2015 Authors: Moore R, Derry S, Aldington D, Cole P, Wiffen PJ

Neuropathic pain is pain coming from damaged nerves, and can have a variety of different names. Some of the more common are painful diabetic neuropathy, postherpetic neuralgia, or post-stroke pain. It is different from pain messages that are carried along healthy nerves from damaged tissue (for example, a fall, or cut, or arthritic knee). Neuropathic pain is treated by different medicines to those used for pain from damaged tissue. Medicines such as paracetamol or ibuprofen are not usually effective in neuropathic pain, while medicines that are sometimes used to treat depression or epilepsy can be very effective in some people with neuropathic pain.

Amitriptyline is an antidepressant, and antidepressants are widely recommended for treating neuropathic pain. Amitriptyline is commonly used to treat neuropathic pain conditions, but an earlier review found no good quality evidence to support its use. Most studies were small, relatively old, and used methods or reported results that we now recognise as making benefits seem better than they are.

In March 2015 we performed searches to look for new studies in adults with neuropathic pain of at least moderate intensity. We found only two additional small studies that did not provide any good quality evidence for either benefit or harm. This is disappointing, but we can still make useful comments about the drug.

Amitriptyline probably does not work in neuropathic pain associated with human immunodeficiency virus (HIV) or treatments for cancer. Amitriptyline probably does work in other types of neuropathic pain, though we cannot be certain of this. Our best guess is that amitriptyline provides pain relief in about 1 in 4 (25%) more people than does placebo, and about 1 in 4 (25%) more people than placebo report having at least one adverse event, which may be troublesome, but probably not serious. We cannot trust either figure based on the information available.

The most important message is that amitriptyline probably does give really good pain relief to some people with neuropathic pain, but only a minority of them; amitriptyline will not work for most people.

Authors' conclusions:

Amitriptyline has been a first-line treatment for neuropathic pain for many years. The fact that there is no supportive unbiased evidence for a beneficial effect is disappointing, but has to be balanced against decades of successful treatment in many people with neuropathic pain. There is no good evidence of a lack of effect; rather our concern should be of overestimation of treatment effect. Amitriptyline should continue to be used as part of the treatment of neuropathic pain, but only a minority of people will achieve satisfactory pain relief. Limited information suggests that failure with one antidepressant does not mean failure with all.

Background:

This is an updated version of the original Cochrane review published in Issue 12, 2012. That review considered both fibromyalgia and neuropathic pain, but the effects of amitriptyline for fibromyalgia are now dealt with in a separate review.

Amitriptyline is a tricyclic antidepressant that is widely used to treat chronic neuropathic pain (pain due to nerve damage). It is recommended as a first line treatment in many guidelines. Neuropathic pain can be treated with antidepressant drugs in doses below those at which the drugs act as antidepressants.

Objectives:

To assess the analgesic efficacy of amitriptyline for relief of chronic neuropathic pain, and the adverse events associated with its use in clinical trials.

Search strategy:

We searched CENTRAL, MEDLINE, and EMBASE to March 2015, together with two clinical trial registries, and the reference lists of retrieved papers, previous systematic reviews, and other reviews; we also used our own hand searched database for older studies.

Selection criteria:

We included randomised, double-blind studies of at least four weeks' duration comparing amitriptyline with placebo or another active treatment in chronic neuropathic pain conditions.

Data collection and analysis:

We performed analysis using three tiers of evidence. First tier evidence derived from data meeting current best standards and subject to minimal risk of bias (outcome equivalent to substantial pain intensity reduction, intention-to-treat analysis without imputation for dropouts; at least 200 participants in the comparison, 8 to 12 weeks' duration, parallel design), second tier from data that failed to meet one or more of these criteria and were considered at some risk of bias but with adequate numbers in the comparison, and third tier from data involving small numbers of participants that were considered very likely to be biased or used outcomes of limited clinical utility, or both.

Main results:

We included 15 studies from the earlier review and two new studies (17 studies, 1342 participants) in seven neuropathic pain conditions. Eight cross-over studies with 302 participants had a median of 36 participants, and nine parallel group studies with 1040 participants had a median of 84 participants. Study quality was modest, though most studies were at high risk of bias due to small size.

There was no first-tier or second-tier evidence for amitriptyline in treating any neuropathic pain condition. Only third-tier evidence was available. For only two of seven studies reporting useful efficacy data was amitriptyline significantly better than placebo (very low quality evidence).

More participants experienced at least one adverse event; 55% of participants taking amitriptyline and 36% taking placebo. The risk ratio (RR) was 1.5 (95% confidence interval (CI) 1.3 to 1.8) and the number needed to treat for an additional harmful outcome was 5.2 (3.6 to 9.1) (low quality evidence). Serious adverse events were rare. Adverse event and all-cause withdrawals were not different, but were rarely reported (very low quality evidence).


http://www.cochrane.org/CD008242/SYMPT_amitriptyline-neuropathic-pain-adults