Prescribing Notes: Pain Assessment

Prescribing Notes: Pain Assessment

Assessment of pain is essential for its correct treatment. As pain is subjective any assessment is best based on the patient's own verbal report and clinical signs. In addition to taking a full clinical and analgesic history, to making a physical examination and psychosocial, assessment, the patient should be questioned on the severity, quality and site of pain, its frequency and duration, and its effect on lifestyle. In chronic pain, a body chart can be used to indicate and to record the site of the pain, while a pain diary and visual analogue scale (VAS) ranging from 0 to 10 can be used to record the severity of pain. Using this approach and continuing it during follow-up, will allow you to assess the efficacy of treatment, to monitor adverse effects and to determine whether continuing pain is related to disease progression or a different cause.

Always attempt to treat the underlying cause of the pain, eg, the use of hormones or hormone antagonists in gynaecological pain, and consider alternative approached or adjunctive therapy if pain is not controlled.

Who Analgesic Ladder
The World Health Organisation's (WHO) analgesic ladder ascending from non-opioids through weak opiodis to strong opiodis according to the severity of the pain is widely regarded as the best approach to the management of acute pain, chronic non-malignant pain, and chronic malignant pain. the objective of treatment in all types of pain, irrespective of origin, is to achieve symptom control and improve the patient's quality of life.

Mild Pain
Analgesics such as aspirin, paracetamol or NSAIDs are indicated for mild pain. They are even effective in patients already receiving strong opioids who develop mild pains such as tension headaches.

Aspirin has analgesic and antipyretic activity and, in higher doses, anti-inflammatory activity. It is particularly effective for tension headache and musculoskeletal pain. It may cause gastric irritation and, because of the risk of Reye's syndrome, should not be used in children except for Still's disease, and then only under close supervision. Dispersible tablets are useful for a rapid effect. Enteric-coated tablets maybe used to reduce gastric irritation but they do delay onset of action.

Paracetamol has analgesic and antipyretic activity, but no anti-inflammatory action. It causes less gastric irritation than aspirin and may be preferable for elderly patients. Solid dose, liquid and suppository formulations are available. It should not be used if there is liver impairment and, in overdose, is dangerously hepatotoxic. Fixed dose formulations combining paracetamol with methionine (Paradote) offer some degree of protection against liver damage should overdose occur.

NSAIDS (non-aspirin) have analgesic, anti-inflammatory and anti-pyretic activity. They can be used to relieve acute pain such as headache, dysmenorrhoea and musculoskeletal pain, or used long term to alleviate chronic pain such as rheumatoid or osteoarthritis, with additional analgesics taken when required for breakthrough pain. In cancer pain they have an opioid sparing effect, and are particularly suitable for pain associated with bone metastases. NSAIDs have ceilings to their efficacy, and patient tolerance and response to NSAIDs is variable. If the desired response is not obtained at the upper limit of the recommended dose, or if side effects are unacceptable, an NSAID from a different chemical class should be tried, they should not be combined.

Moderate Pain
Weak opioids used alone or in conjunction with mild analgesics are the treatment of choice for moderate pain. Dextropropoxyphene with paracetamol (co-proxamol), dihydrocodeine with paracetamol (co-dydramol), codeine with paracetamol (co-codamol) and codeine with aspirin (co-codaprin) are usually used first-line. However, the low content of the weak opioid in these preparations means that they are usually only effective in treating mild to moderate pain. If a greater analgesic response is required, proprietary fixed-dose combinations such as Kapake, Remedeine, Solpadol - or Tylex, which have a greater dose of weak opioid than the standard formulations, should be employed.

Towards the top end of the moderate pain scale, fixed dose combinations may be less suitable because of the risk of exceeding the maximum dose of the non-opioid. In such circumstances, it is better to use codeine, dihydrocodeine or tramadol as single ingredient formulations, adding in paracetamol, aspirin or an NSAID separately if required. Weak opioids, particularly codeine, can cause severe constipation. Laxatives may be used prophylactically rather than being witheld until constipation develops. Tramadol is considered to be almost non-constipating.

Severe Pain
Strong opioids such as morphine, diamorphine, fentanyl, buprenorphine, dextromoramide, methadone, oxycodone and phenacozine may be required for most forms of severe continuous pain such as cancer pain but may not be very effective in neuropathic pain. Intermittent pain does not respond well to opioids. Strong opioids may also be used in severe musculoskeletal pain, but long term use should be avoided. Morphine is the most commonly used of the strong opioids and is particularly suitable for severe continuous pain of visceral or soft tissue origin.

When initiating therapy, start with an oral dose of 2.5 mg to 5 mg four hourly. Titrate by increasing the dose by 50 per cent to 100 per cent every four hours until pain is controlled. Once control is established switch to a sustained-release formulation with a dose interval of 12 hours (MST Continus or Oramorph SR) or of 24 hours (Morcap SR, MXL capsules). It is imperative that doses are given "around the clock"; do not wait until the patient experiences pain. If there is breakthrough pain, immediate release formulations should be given at 1/6th of the total daily dose. Review regularly the total daily dose and adjust the dose of the sustained-release formulation if necessary.

Contrary to popular misconception, there is no maximum dose for morphine in such circumstances. When used to control true continuous pain, there is no danger of addiction, tolerance or respiratory depression. As long as with each incremental dose an incremental degree of analgesia is obtained, then it is safe to continue to titrate upwards to optimum pain control. There is no ceiling effect. Constipation with morphine is severe, so laxatives such as co-danthramer or co-danthrusate must be used prophylactically from the start of therapy in malignant pain. Liquid formulations of morphine are available for patients who have difficulty in swallowing. For parenteral administration, eg when the patient is unable to swallow or there is persistent vomiting, diamorphine is preferable to morphine since its greater solubility allows a smaller dose volume. It is usually given subcutaneously at 1/3 rd the oral dose of morphine.

Transdermal fentanyl (Durogesic) is an alternative to morphine in the relief of chronic intractable cancer pain. Each patch provides 72 hours continuous pain relief equivalent to that of morphine, but possibly with a lower incidence and severity of constipation. The strength of patch chosen depends on the patient's opioid history. Opioid-naive patients or those taking weak opioids should start with the 25 microgram/hr patch. Opioid tolerant patients should use a patch strength based on the previous 24 hour morphine (or equivalent) dose (morphine 24hr dose:patch- 0-135 mg:25 microgram/hr; 135-224 mg:50 microgram/hr; 225-314mg:75 microgram/hr; 315-404 mg:100 microgram/hr). As it can take 24 hours to reach optimal plasma levels, previous analgesic therapy should be continued during this period. Assessment of analgesic efficacy should be made after 72 hours. Immediate release oral morphine must be available prn to cope with breakthrough pain or symptoms of withdrawal.

When the patient has pain that responds to morphine but cannot tolerate side effects, oxycodone, phenazocine (Narphen) and methadone may be used. Oxycodone as suppositories can be useful when oral therapy is no longer possible and obviates the need for a syringe driver. Phenacozine has a short half-life permitting severe pain to be treated promptly without the risk of accumulation. Methadone may be a useful analgesic in occasional patients who have severe chronic pain that is non-responsive to morphine. Transfer using a dose of methadone of 10 per cent of the daily morphine dose but, because methadone has a long half-life, dosages should be prescribed 8-12 hourly. Regular users/abusers of opioids may require larger doses than normal for acute painful episodes.

Adjunctive Therapy
Some types of pain, eg, bone pain, incident-related pain, nerve and cerebral compression pain, and neuropathic pain are only partially responsive to opioids and may require adjunctive therapy. Adjuvant drugs can be used at all stages of the analgesic ladder to enhance the analgesic effect. Corticosteroids can be considered for patients with neuropathic pain from nerve compression or infiltration, bone pain, hepatomegaly, and raised intracranial pressure.

Dexamethasone and betamethasone are the drugs of choice due to their high glucocorticoid activity relative to their mineralocorticoid activity. They have an anti-inflammatory effect and reduce compression pain by reducing oedema. Although not all are licensed, low doses of antidepressants (amitriptyline, desipramine, imipramine, mianserin), anticonvulsants (clonazepam, carbamazepine, valproate) and antiarrhythmics (lignocaine, flecainide, mexilitine) have been shown to be of value in neuropathic pain. Diazepam can be used to relieve associated muscle spasm in musculo-skeletal pain but should only be used for the acute episode.

Physical measures such as rest/ice/compression/elevation (RICE) or aspiration of effusions may also be used to relieve musculo-skeletal pain associated with sprains and strains. If pain control cannot be achieved by drugs, non-pharmacological procedures such as acupuncture, transcutaneous electrical nerve stimulation (TENS) and neuronal blockade may be performed in specialist centres.

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