Use of Analgesics in mental health

 In Mental Health, Pharmacy Information

Pain is a commonly experienced symptom and this article looks at some points to consider when prescribing analgesics for patients with a mental health condition.

There are four main groups of analgesic drugs:

Paracetamol

Paracetamol is a widely used drug and is relatively safe at the recommended daily dose of 4 grams for adults. However, it is a very toxic in overdose with single doses as small as 10 grams being enough to cause liver damage. Where the liver is already compromised by, for example, excessive alcohol consumption or an eating disorder toxicity can occur with as little as 5 grams.

In the UK, paracetamol overdose is the leading cause of admission to hospital due to poisoning and is a major cause of acute liver damage. Therefore, it is essential that service users who are prescribed paracetamol and who are deemed to be at high risk of self-harm or suicide are regularly assessed to ensure that they only have access to an appropriate number of tablets. This can sometimes be difficult to manage, for example during a weekend leave.

For inpatients, using the soluble tablets or liquid formulation will prevent patients from hoarding supplies and reduce suicide risk.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

The NSAIDs include aspirin, ibuprofen, naproxen and diclofenac. They work by reducing the production of inflammatory mediators in the body called prostaglandins. As well as mediating inflammation, prostaglandins modulate blood flow, platelet aggregation and kidney function.
NSAIDs may reduce kidney function. Ibuprofen and diclofenac have been shown to raise lithium levels by on average 23% and 25%, which can lead to lithium toxicity. Increased monitoring of lithium plasma levels is recommended for patients taking NSAIDs as the dose of lithium must be kept within its narrow therapeutic range.

NSAIDs also increase the risk of bleeding due to a reduction in platelet aggregation, and cause an especially large increase in the risk of an upper GI tract bleed as prostaglandins also exert a protective effect here. Selective serotonin re-uptake inhibitors (SSRIs) and venlafaxine also have been shown to reduce platelet aggregation, and service users taking these with an NSAID have been shown to have an increased chance of an upper GI bleed.

Opioids

The opioid analgesics include codeine, morphine, diamorphine and methadone. They can cause addiction, so must be used with caution for patients with personality disorder or a history of addiction. Simulation of symptoms in order to gain opioids is common, but this risk shouldn’t prevent patients from receiving treatment. Opioids commonly cause drowsiness, which can be exacerbated by other psychotropic drugs.  Higher doses can also cause respiratory depression, which can be worsened with benzodiazepines. This combination can increase mortality risk particularly with illicit use. Opioids cause constipation, and this is made more severe by antimuscarinics drugs such as clozapine. This can increase the risk of the development of ileus, a potentially life threatening complication, where the gastrointestinal tract becomes completely blocked.

Tramadol has noradrenergic and serotonergic action in addition to its opioid effects. This can increase the risk of side-effects with antidepressants such as tricyclics and SSRIs and may lead to serotonin syndrome.

Nefopam

Nefopam is a centrally acting non-opioid analgesic which is chemically related to the anti-muscarinic drug, orphenadrine. It has anti-muscarinic side effects and so is liable to increase the same side effects in other drugs that cause these such as clozapine and the tricyclic antidepressants. People taking mono-amine oxidase inhibitor (MAOI) antidepressants are advised not to take nefopam due to the risk of a build-up of excitatory neurotransmitters.

Nefopam can sometimes cause false positive readings on urine screening drugs tests, causing service users to appear to test positive for benzodiazepines or opioids when none have been taken.

Summary
There are a number of important cautions and interactions to consider when prescribing analgesics for service users with a mental health diagnosis. However, by taking into account these factors it is usually possible to prescribe an effective, safe and well tolerated analgesic regimen.

 

Written by:

Matthew Roberts,

Clinical Pharmacist

 

By Katy Warner from Orlando, FL, USA (rapid release (02-18-08)) [CC BY-SA 2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

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