Indelicato and Portenoy reported a method for dosing when switching between opioids in a patient with refractory cancer pain. The authors are from Beth Israel Medical Center in New York City.
(1) Determine the equianalgesic dose for the new opioid.
(2) Reduce the equianalgesic dose based on the new opioid selected.
Equianalgesic Dose Adjustment
do not reduce
reduce by 75-90% (median 82%)
reduce by 25-50% (median 37%)
(3) Adjust the dose based on patient characteristics.
more of a dose reduction
significant comorbid condition
less of a dose reduction
(4) Calculate a rescue dose as 5-15% (median 10%) of the total daily opioid dose and administer it at an appropriate interval.
(5) Titrate the dose based on severity of pain, severity of side effects and number of rescue doses administered.
Rationale for reducing opioid dose with this method:
(1) Cross tolerance between opioid drugs may be incomplete. A high dose of a longer acting opioid may result in serious side effects.
(2) There is a large interindividual variability in the relative potencies among opioid.
(1) This method does not address the half-life or duration of analgesic effect for each agent.
(2) If transdermal fentanyl is selected for baseline analgesia, another agent with a quicker onset of action is needed to for the rescue dose.
Comparison with the method of Nelson et al (see previous section):
(1) Nelson did not reduce the equianalgesic dose when using parenteral morphine. Nelson's patients were on continuous therapy for terminal cancer pain.
(2) The rescue dose was about 2% of the daily dose opioid dose but was given every 2 hours (up to 12 times a day).
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Specialty: Pharmacology, clinical