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Which opioid to choose?

This article describes the principles of choosing a strong opioid.
Boxes of medication on shelves in a dispensary
© Newcastle University
Terry and his GP agree that he needs a strong opioid but which opioid to choose?

Morphine is the strong opioid of choice

The most common reason to start with an opioid other than morphine is renal failure (which we will cover later in this course). Some patients report that they are allergic or intolerant of morphine, based on previous experiences. True allergy to morphine is very rare so any reported reason not to prescribe it should be investigated. Often the starting dose was too high or side-effects had not been proactively managed (again we cover these issues later in the course). It’s worth noting that opioid side-effects can be very unpleasant and may leave a lasting impression. Clinicians should therefore provide their patients with clear explanations and plenty of reassurance if necessary.

Oral administration is the route of choice

Exceptions to this are, if the patient is unable to swallow, is vomiting or if absorption from the gastro-intestinal tract is known to be poor (for instance in subacute bowel obstruction). If the oral route is not an option, the strong opioid should be given subcutaneously. We will show you how to prescribe this later in this section.
Never prescribe transdermal opioids (patches) for pain which is unstable.
This includes the initiation of a strong opioid (i.e. when moving to step 3 of the WHO analgesic ladder). This is because, by definition, the pain is not controlled at step 2 of the ladder.

Starting dose

When calculating the starting dose of a strong opioid, you must take into consideration any weak (step 2) opioids that the patient is already taking. This is because drugs like codeine and tramadol are equivalent in strength to morphine. If this is not factored in, the patient may actually take less opioid analgesic at step 3 than they did at step 2.
In the next section we will take you through the process of safely initiating a strong opioid. In practice, if you are uncertain or if your patient is complex you should always consult available guidance and/ or seek specialist advice.
© Newcastle University
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