Prescribing analgesia

When assessing pain, ensure you begin by taking a history to characterise the pain as neuropathic pain, inflammatory pain and oncological pain all respond to different analgesia. SOCRATES is a helpful way to systematically take this history as it will help identify any serious underlying disease that is causing the pain and whether any further investigations or assessment is required.

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Introduction

Before prescribing analgesia, ensure you check the renal function & for any contraindications (allergy, peptic ulcer for NSAIDs etc.). Their weight is also important, for example, lower doses of paracetamol are used in those under 50kg to avoid toxicity.

WHO Ladder

The WHO analgesic ladder is a commonly used tool to escalate analgesia in a stepwise fashion. However, it is designed predominantly for cancer-related pain and therefore may not be the most appropriate strategy for every patient.

Before you escalate above the ladder, consider:

  • If analgesia is prescribed regularly, is it at its maximum dose?
  • If analgesia is prescribed on the PRN side, has the patient used it at its maximum frequency?
  • Has analgesia been prescribed according to the pain ladder?
  • What type of pain is it and is the prescribed painkiller appropriate? E.g. neuropathic pain responds better to amitriptyline, duloxetine, pregabalin, gabapentin & trigeminal neuralgia responds better to carbamazepine
Step 1: Non-opioid ± adjuvants
  • Paracetamol 1 gram QDS: Those with low body weight (e.g. <50kg) or with risk factors for hepatotoxicity should receive 500mg QDS.
  • ± NSAIDs e.g. Ibuprofen 200/400mg TDS. PPIs (e.g. Lansoprazole 30mg OD) should be considered in any patients who are at higher risk for gastric ulceration. Avoid use in the elderly, those with gastric ulcers, asthma or AKI/CKD & be cautious in those with congestive cardiac failure.
  • Adjuvants can be additionally used depending on the type of pain (see more below).
Step 2: Above & weak opioid
  • Codeine 30-60mg QDS. It can cause quite significant constipation, so all patients should be prescribed PRN laxatives and have their bowels monitored. Due to genetic differences, it may not be effective in all patients so if there is no response at all, consider switching to another drug.
  • Alternatively, consider Tramadol 50-100 mg QDS. It is usually more potent than codeine & may have some neuropathic pain targets
Step 3: Above & strong opioid
  • If on the maximum dose of weak opiates, consider morphine sulphate oral solution (a.k.a. “oramorph”) 2.5-5mg every 4 hours on the PRN section for breakthrough pain. It is good practice to prescribe this with antiemetics, laxatives and naloxone (although nursing staff should always inform a doctor if they give naloxone!).
  • Seniors may recommend larger or more frequent dosing in a young patient with a large build
  • Elderly, frail or patients with reduced GCS should be given the lowest possible doses & be discussed with seniors
  • For patients with impaired renal function (AKI or CKD), oxycodone is frequently used instead. Note that it is twice as strong (i.e. 10mg oral morphine solution = 5mg oral oxycodone solution)
Step 4: Converting PRN opiates to regular
  • If the patient is requiring regular PRN doses then they should be started on modified-release preparations to give better cover throughout the day. Aim to stop the weak opiate when giving regular strong opiates.
  • Calculate this by totalling 24 hours worth of opiate dosing from the PRN section & splitting an amount just below this across twice daily modified-release preparations. For example, if a patient takes 35mg of oramorph per 24 hours, then split 30mg over two doses: Morphine sulphate tablets 15mg BD
  • Continue the PRN doses at 1/6th of the total dose. In our above example, 35mg/6 = 5.8mg. Therefore, you could prescribe 5mg oramorph on the PRN section
  • Remember to also prescribe antiemetics, laxatives and naloxone on the PRN side as above
  • Be wary that subcutaneous preparations are twice as strong as oral. Therefore: 10 mg oral morphine = 5 mg subcut morphine = 5 mg oral oxycodone = 2.5 mg subcut oxycodone
  • You are not expected to start buprenorphine/fentanyl patches nor start methadone prescriptions without direct supervision
  • Pallcare.info offers a great tool for opiate conversion in patients or you can talk to your seniors & the acute pain team

Acute Pain Team

This service is often provided by specialist nurses (with support from usually a consultant anaesthetist) who advise on best pain management strategies. They are excellent at giving advice on appropriate agents, different types of pain, opioid conversions and advanced opiates such as patches or PCA. They are very helpful – but before contacting them, make sure that the WHO analgesic ladder is applied correctly or this will be their first advice.

Other types of pain

  • For MSK conditions, paracetamol and NSAIDs more effective. TENS machines can also be considered.
  • For inflammatory pain, NSAIDs are highly effective e.g. gout, dysmenorrhoea. These can be given topically if the pain is localised. For osteoarthritis, lidocaine patches over the area, ice or intraarticular steroids can all be effective.
  • For neuropathic pain, consider amitriptyline or gabapentin. Capsaicin cream is an alternative option but can be significantly more expensive
  • For migraines, triptans can be very effective
  • For cardiac pain, GTN can be more effective
  • For gastrointestinal pain (e.g. cramps), buscopan can be very helpful

Further Tips

  • Be wary of paracetamol. It is easy to prescribe paracetamol with another paracetamol containing product e.g. co-codamol which can result in overdose
  • Avoid combining regular opiates e.g. codeine, tramadol & oramorph. They can cause confusion, drug errors and unpredictable overdose
  • Remember you can always give more strong opiates should the patient remain in pain. You do not need to give large doses you are uncomfortable with from the start as you can always assess the patient in 1-2 hours, to review if they need some more. This is safer than giving a patient respiratory compromise.
  • Consider PRN antiemetics, laxatives and naloxone. Naloxone has a short half-life therefore infusion or repeated doses are likely to be necessary.
  • Seek senior or expert guidance before starting a patient newly on a opiate patch
  • Discuss patients who have bowel obstruction or surgery with your seniors before prescribing laxatives with opioids
  • Consider alternatives to opiate analgesia in those with chronic pain that is non-malignant. Long term dependence on opiates is unlikely to be beneficial in the long term

Useful Resources

Written By Dr Saman Jalilzadeh Afshari (FY2)
Edited by Dr Akash Doshi (ST3)

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4 thoughts on “Prescribing analgesia”

  1. I just had one question. You mention when changing from step two to step 3 you calculate the 24hr dose of PRN oromorph and convert this to equivalent MST dose and prescribe, however shouldn't you total the codeine and PRN oromporph dose to give you a 24hr value which is then converted to MST dose.

  2. Excellent question! Technically you are completely correct – 30mg QDS would be the equivalent of 12mg oral morphine. However, we tend to reduce dosing by ~25% when we convert up for safety & because often the patients don't need as much when they've got good background control. Provided appropriate PRNs are written up this shouldn't cause any issues. Hence I don't include the codeine in these calculations.

    If you're curious why, there's at least 3 reasons:
    1) Converting shorter acting opiates to longer acting ones risks overdoing the dose with prolonged & more concerning adverse effects.
    2) A feature called incomplete cross-tolerance – the built up tolerance to a certain opiate doesn't completely transfer to another opiate so they might experience more adverse effects particularly in the elderly.
    3) About 6-10% of caucasians lack CYP2D6 which means codeine has no effect. Lower doses of morphine may be enough for them.

  3. So if I understand this correctly. If I gave 15 mg oramorph MR tablets BD as a regular. I can add also give 1/6th of that PRN which is 5 mg.

    So the prescription chart would be:

    Regular: PO 15 mg morphine sulfate MR tablet BD

    PRN: PO 5 mg oramorph solution 4 hourly

    Is that correct?

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