Other analgesics

Summary of recommendations: other analgesics

Topicals

There are a number of topical agents including rubefacients and capsaicin products. They may previously have had a role in therapy, but there is limited evidence for their clinical value.

Topical rubefacients

Indications and effectiveness

• Many rubefacients or counter irritants have been identified as items of low clinical value and should not be prescribed on the NHS.
• Rubefacients are topical preparations that may contain nicotinate compounds, salicylate compounds, essential oils, and camphor. They cause irritation and reddening of the skin due to increased blood flow.
• They have been used to relieve pain in musculoskeletal conditions, however this is not supported by the most recent published evidence.
• Menthol e.g. menthol in aqueous cream can give additional benefit, cooling the skin for several hours. This is available in a variety of strengths.
• Individuals can be signposted to non-pharmacological heat and cold therapies, such as hot water bottles, microwavable wheat bags and reusable gel warmers, icepacks and cooling gel packs.
  
  

Risks and harms

• Adverse effects are usually limited to localised reactions such as dry skin, reddening, burning sensations and contact dermatitis. Individuals may be advised to test on a small area of skin first.

Capsaicin

Indications and effectiveness

• Capsaicin products have a limited place in therapy.93 See licensed indications in the table below.
• Capsaicin reduces pain messaging to the spinal cord and to the brain, by desensitising sensory (nociceptive) nerve fibres.
• Capsaicin is available as a cream or as a cutaneous patch (see the table below for licensed indications).
• Patch use is generally reserved to specialist clinics as there are specific application and monitoring requirements.
• Individuals may or may not feel the warming sensation on application and should be advised this is not linked to efficacy of the product.

 

Licensed indications for use of capsaicin

Please note that the table below may need to be scrolled horizontally or vertically in order to view all information, depending on your device.

Product	Indication	Dose	NNT
0.025% Cream	Osteoarthritis	Apply three to four times daily not more often than every four hours	Not known
0.075% Cream	- Post herpetic neuralgia - Painful diabetic neuropathy	Apply three to four times daily not more often than every four hours	Not known
8% cutaneous patch	- Peripheral neuropathic pain	Applied under specialist supervision	11-1294

Risks and harms

With creams:

• Individuals should be advised to wash hands immediately after use and avoid hot showers or baths just before application.
• Localised burning sensation if too much applied or applied too frequently.
• Some people report increased cough and they should be advised to report any exacerbation of pre-existing asthma conditions.

Nefopam

Indications and effectiveness

• Nefopam is a non-opioid, centrally-acting analgesic. The mechanism of action is not well understood. It is known to inhibit the re-uptake of neurotransmitters including serotonin, noradrenaline and dopamine
• There is limited clinical evidence available for the effectiveness of nefopam in the treatment of chronic pain as outlined in Scottish Government guidance on medicines of low and limited clinical value
• Nefopam may be considered for specific individuals⁹⁵, when choice of alternative analgesia is limited due to other co-morbidities e.g. people with renal failure
  • Particular caution should be used in adults who would be at elevated risk of anticholinergic side effects e.g. older adults or in cognitive impairment
• There is no evidence that nefopam is more potent than non-steroidal anti-inflammatory drugs (NSAIDs), but is commonly associated with adverse drug reactions and is toxic in overdose^95,96
  
  

Risks and harms

• Common side-effects include: confusion, nausea, nervousness, urinary retention, dry mouth, light-headedness. It is toxic in overdose
• Nefopam scores two on the anticholinergic burden scale (ACB) therefore sympathomimetic and antimuscarinic side-effects may be troublesome
  • Confusion and urinary retention are a particular problem in the elderly

The side effects of nefopam can be cumulative with other anticholinergic medications see Scottish Government Polypharmacy Guidance.  

Lidocaine plasters

Indications and effectiveness

• Lidocaine plaster use should be limited to licensed indications for pain relief.
• This is symptomatic relief of neuropathic pain associated with previous herpes zoster infection (post herpetic neuralgia) in adults (see Scottish Medicines Consortium advice). Its use is restricted to individuals who are intolerant of first-line systemic therapies or where these therapies have been ineffective.
• The place in therapy of lidocaine medicated plasters is currently unclear. Evidence supporting both their licensed use in post herpetic neuralgia and in other unlicensed indications is limited.
• NICE guidance on chronic pain does not recommend lidocaine plasters for treating neuropathic pain. 

Risks and harms

• Caution in use in severe renal impairment.

Medicinal cannabis

Indications and effectiveness

Cannabis-based medicinal products (CBMP) should not be prescribed for chronic pain due to the low numbers of NNH (6) and the high number of NNT (24)⁹⁷.

CBMPs have been shown in some systematic reviews to have a low to moderate effect on chronic pain^98-106. However, the studies included in these reviews have often been considered low quality and the effect shown has not been considered clinically important. 

Risks and harms

Participants receiving CBMPs were more likely to experience side effects compared with placebo. These included anxiety, attention disorder or deficit, confusion, delusions, depression, suicidal thoughts, disorientation, dizziness, euphoria, falls, hallucinations, mania, memory impairment, nausea, paranoia, sedation, diarrhoea and vomiting.

Although trials of CBMPs in pain have shown limited serious adverse effects the trials are usually of short duration. High-quality harms data from long-term controlled studies for chronic non-cancer pain are lacking. 

Methocarbamol

Indications and effectiveness

• It is licensed for short term symptomatic treatment of acute painful muscular tension, especially in the lower back in adults.
• Methocarbamol is a centrally acting muscle relaxant which does not directly relax tense skeletal muscles.
• There are few high-quality studies and no meta-analyses comparing methocarbamol to placebo or alternative agents for muscle spasms.
• It is less suitable for prescribing due to clinical efficacy not being well established.

Risks and harms

Side effects include: confusion, convulsions, drowsiness, restlessness, anxiety, hypotension, vertigo, nausea and vomiting.

• If methocarbamol is used concomitantly with centrally acting drugs such as barbiturates, opioids and appetite suppressants, the effects can be mutually enhanced
• The consumption of alcohol during treatment with methocarbamol can increase the effect
• The effects of anticholinergics, such as atropine and some psychotropic drugs, may be potentiated by methocarbamol
• Methocarbamol may reduce the effect of pyridostigmine bromide. Therefore, methocarbamol should not be used by people with myasthenia gravis, particularly those being treated with pyridostigmine

Benzodiazepines

Indications and effectiveness

• There is no indication in chronic pain, specifically:
  • Sciatica (lumbar radiculopathy): benzodiazepines should not be used
  • chronic primary pain in people aged 16 years and over: NICE recommends ‘do not initiate benzodiazepines to manage this’

Risks and harms

• Adverse events are considered as cognitive (memory loss, confusion, disorientation), psychomotor (reports of dizziness, loss of balance, or falls); and morning hangover effects (residual morning sedation)
• The number needed to harm for any adverse event is 6
• Older adults and frail people are more susceptible to adverse effects and harms
• Increased risk of respiratory depression if prescribed with an opioid
• Consider the total benzodiazepine-type medicine load prescribed per day – as benzodiazepines, z-drugs and gabapentinoids provide synergistic effects such as sedation and respiratory depression