Opioid Dosing

The pronounced individual variability in opioid response, combined with changes in responsiveness over time, mandates individualization of opioid doses based on a continuing process of assessment (analgesia and adverse effects) and dose titration. Table 18.3 lists the recommended starting doses for moderate-to-severe pain in the postoperative period for opioid-na'ive patients. If a patient is not receiving enough pain relief at a given dose, increase the dose by 25-50%. If a patient is having pain before the next dose is due, reduce the interval and/or increase the dose.

Rotation from one opioid to another may be necessary in several circumstances. One situation is if a few attempts have been made at increasing the dose of an opioid, such that a patient is on a "reasonable" dose and they are still not receiving any pain relief, rotation to a different opioid may provide better analgesia. A second situation is if a patient is having intolerable side effects not treated with appropriate agents, again rotation to a different opioid may provide a better side effect profile. A third situation is if a particular opioid is not available by the route of administration required in a given patient. A fourth situation would be if a patient has been on an opioid for an extended period of time and is

Table 18.3 Recommended starting doses of opioids for adults over 50 kg.

Agonist

Oral

Intravenous (IV)

Codeine

15-60 mg q 3-4 h

n/a

Hydrocodone

5-10 mg q 3-6 ha

n/a

Tramadol

50-100mg q 4-6hb

n/a

Oxycodone

5-10mg q 3-4h

n/a

Morphine

10-30 mg q 3-4 h

5-10mg q 2-4h

Hydromorphone

2-6 mg q 3-4h

1-1.5 mg q 3-4 h

Oxymorphone

10-20 mg q 4-6 h

1 mg q 3-4 h

n/a = not applicable.

aDaily dose limited by acetaminophen component in available preparations bMaximum recommended 24-h dose: 400mg in adults <75 years old; 300mg in adults

>75 years old.

n/a = not applicable.

aDaily dose limited by acetaminophen component in available preparations bMaximum recommended 24-h dose: 400mg in adults <75 years old; 300mg in adults

>75 years old.

demonstrating signs of tolerance to the analgesic effects, again rotation to a different opioid may provide better analgesia, usually at less than the expected equianalgesic dose due to incomplete cross-tolerance. This means that patients will not be "as tolerant" to the new opioid agonist as they were to the one they were on previously. Thus, when converting between opioids, for any of the reasons mentioned, the calculated equianalgesic dose of the new agent must be reduced by 25-75% in order to prevent over-sedation and/or respiratory depression.

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