What is an opioid?

  • A drug that acts on opioid receptors
  • Opiates are a subset of opioids, which occur naturally, such as morphine
  • Opioids are commonly used to treat acute pain, and as co-induction agents for general anaesthesia
  • They are also used in regional anaesthesia techniques such as epidural and spinal blocks
  • Side effects include nausea and vomiting, respiratory depression, pruritus, constipation and confusion


  • Recall the pertinent chemical, pharmacokinetic and pharmacological properties of FentanylAlfentanilRemifentanilMorphine and Diamorpine
  • Compare and contrast the properties of these drugs and their clinical uses in anaesthetic practice
  • Use this knowledge and understanding to select an appropriate opioid for use at induction, for regional anaesthesia, for Awake Fibreoptic Intubation and for intra/post-operative analgesia in various clinical scenarios






What you need to know

  • Diamorphine = Heroin = Diacetylmorphine
  • Diamorphine has no intrinsic activity at opioid receptors
  • Once it is deacetylated, it can exert its effect in the form of morphine
  • 1mg Diamorphine = 2mg Morphine
  • Diamorphine is much more lipid-soluble than morphine, making it ideal for use in neuraxial anaesthesia (spinal / epidural) where barriers such as the dura need to be crossed in order for it to exert its effect

Try our Opioid MCQ Quiz

Created on By unicyclemedic


Test your knowledge of the commonly used opioids

1 / 15

Which of the following best explains why Alfentanil has a shorter duration of action than Fentanil?

2 / 15

Which of the following statements regarding Fentanyl is incorrect?

3 / 15

Which of the following is not a synthetic piperadine derivative?

4 / 15

Which Target-Controlled Infusion (TCI) model is used for Remifentanil?

5 / 15

Which of the following statements regarding opioids is incorrect?

6 / 15

A 35-year-old gentleman with a known grade 4 airway is scheduled on the emergency list by Maxillofacial Surgeons for extraction of dental abscesses. Your consultant plans to perform an Awake Fibre-Optic Intubation (AFOI) on this patient. In additional to topicalising the airway and vocal cords with local anaesthetic, which agent would be appropriate to give to facilitate this?

7 / 15

You are performing a modified RSI on a 20-year-old male patient for a laparoscopic appendicectomy. He is ASA1 and weighs 75kg. You have drawn up 200mg Propofol and 100mg Rocuronium ready for induction. You have also readied 10mg Morphine for intra-operative analgesia. Which of the following opioids would be appropriate to give at induction?

8 / 15

You have consented a 65-year old lady for General Anaesthetic and Spinal Anaesthetic for her Emergency Laparotomy for large bowel obstruction. She has a background of hypertension and mild asthma but has an excellent exercise tolerance. She is cardiovascularly stable.

A Spinal Anaesthetic is performed awake and the opioid is intended to provide post-operative pain relief.


Which of the following is the most appropriate opioid to inject intrathecally for this patient?

9 / 15

A 73-year-old lady is day 2 post-op for a laparotomy and is on a PCA to manage her pain. A decision was taken to use Fentanyl in the PCA as she has Chronic Kidney Disease (stage 4). The PCA is delivering 20mcg boluses (there is no background infusion). She has pressed her button 28 times in the past 24 hours. What is the equivalent dose of morphine she has received over the past 24 hours?

10 / 15

Which of the following is correct regarding Morphine?

11 / 15

You are asked to anaesthetise a 52-year-old male with a background of hypertension and NIDDM for an open inguinal hernia repair. You gave 230mg Propofol + 100mcg Fentanyl at induction and then maintain anaesthesia with Desflurane. You then choose to give Morphine for more prolonged analgesia.

Which of the following doses of Morphine is equivalent to 100mcg Fentanyl?

12 / 15

Which of the following is the most appropriate opioid to be used at induction as a bolus?

13 / 15

Morphine's slow onset is explained by which of the following?

14 / 15

Which of the following statements regarding Alfentanil is incorrect?

15 / 15

Which of the following is metabolised to inactive compounds by ester hydrolysis?

Your score is

The average score is 80%


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