Opiates

Opiate medication is your first choice for analgesia when patients rate their pain as moderate or severe.

RCEM recommends intravenous morphine, 0.1-0.2 mg/kg initially in patients with severe pain. Intramuscular or subcutaneous administration should be condemned, given the delayed absorption via this route and the pain involved in (repeated, perhaps) delivery.

Codeine or tramadol have a role in moderate pain.

Morphine

Morphine is likely to be the most widely used opiate in the ED. It is also the standard with which other opiates are compared.

One of the downsides to opiates in general is the variability in patient response. So do encourage frequent reassessment of pain scores and be prepared to prescribe further increments.

Morphine reaches peak effect within a few minutes when given intravenously and in general provides clinical effect for three to four hours.

Learning Bite

The College recommends intravenous morphine 0.1- 0.2mg/kg initially in patients with severe pain.

Diamorphine

Fig. 13 Diamorphine Hydrochloride (ampule)

Whilst there are no differences between parenteral diamorphine and morphine in terms of analgesia and side-effects, diamorphine can be absorbed (rapidly) by the transmucosal route.

This has given it a proven role intranasally in children⁴ and is an option in adults with difficult venous access.

Fentanyl

Fig. 14 Fentanyl (ampule)

The key advantage of fentanyl over morphine is its brief action, providing analgesia for 30-45 minutes, thereby giving it a role in procedural sedation. It can be administered intranasally to adults and is rapidly absorbed by the transmucosal route.

Ultra-short acting opiates have been developed such as remifentanil (duration of action <6 min) and alfentanil (about 10 min).

Whilst there are theoretical benefits, you should consider governance and training issues before using them. Besides, the more widespread use of propofol for procedural sedation is likely to limit the role of ultra-short acting opiates.

Codeine

Recommended by the College, codeine nevertheless has several limitations as an oral opiate:

• It compares poorly with both paracetamol and ibuprofen, even in doses of 60 mg
• Most of its analgesic effect is as a result of metabolism to morphine – nearly 10% of Caucasians and 1-2% of Asians lack the required enzyme

Learning Bite

Codeine compares poorly with paracetamol and ibuprofen, even in doses of 60 mg.

Tramadol

Fig.15 Tramadol hydrochloride (capsules)

Tramadol is widely used in continental Europe. Not all its effects are via opiate receptors.

The maximum dose is 100 mg every four hours.

Tramadol enjoys a much better safety profile than other opiates, notably less risk of respiratory depression.

Common adverse side effects of opiates

• Sedation (hence respiratory depression)
• Nausea and vomiting
• Histamine release causing pruritus and (mild) hypotension
• Slowing of gastrointestinal function (constipation)
• Urinary retention

The adverse effects tend to be dose related.

In general, opiates are metabolised in the liver and excreted in the kidneys. Hence there is a tendency to greater and longer lasting desired and undesired effects from accumulation in patients with liver and kidney dysfunction.