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Opioid-naïve patients with severe pain should generally begin one of
the opioids conventionally used for severe pain at a dose equivalent to,
or less than, 5 to 10 mg parenteral morphine every 3 to 4 hr. Equivalent
doses of these opioids are calculated from the relative potency ratios published
in equianalgesic dose tables (Table 1). A switch to a new opioid, or a new
route of administration, is also accomplished by consulting an equianalgesic
table. The doses indicated on this table should be viewed as broad guidelines,
the use of which must be tempered by clinical judgment and the condition
of the patient (Table 2).
Table 1: Equianalgesic Opioid Doses (.pdf)
Table 2: Empirical Guidelines for Opioid Rotation (.pdf)
Individualization of the opioid dose is accomplished by dose titration,
the goal of which is adequate analgesia without intolerable and unmanageable
side effects. Titration of the opioid dose may be necessary at the start
of therapy and repeatedly during the patient’s course.
Because the concentration-response relationship for opioid drugs is best
characterized as log-linear, dose increments are best considered as percentages
of the existing dose, rather than any absolute amount. A dose increment
of 30-50% is safe and usually large enough to observe a meaningful change
in effects. If pain is severe and the patient is not predisposed to opioid
toxicity, a higher increment, up to 100% of the existing dose, may be considered.
This percentage dose increment applies irrespective of the specific opioid
or route of administration. The calculation should include both the fixed
schedule drug and the as needed drug.
An alternative approach to dose titration is possible in those who are coadministered
an “as needed” opioid dose for breakthrough pain. The total
amount of supplemental drug used during the prior day or two can be summed
and converted into the fixed scheduled administration. Whatever the amount,
safety is assured if the patient has tolerated it during the prior day.
The milligram opioid dose is immaterial as long as the patient attains a
favorable balance among analgesia, other functional goals, and side effects.
One retrospective survey of 100 cancer patients with challenging pain problems
found that the average daily opioid requirement was equivalent to 400 mg
to 600 mg of parenteral morphine, but approximately 10% of patients required
greater than 2000 mg and one patient required over 30,000 mg/24 hr. Based
on most surveys, patients with chronic nonmalignant pain usually will require
less than a dose equivalent to few hundred milligrams of oral morphine per
day. If a patient requires a relatively high dose, careful assessment is
needed to ensure that the outcomes (including analgesia and side effects)
are consistently favorable and responsible drug-taking is occurring.
References
Hanks GWC, Cherny N, Fallon M. Opioid analgesic therapy. In: Doyle D, Hanks GWC, Cherny NI, Calman K, eds. Oxford Textbook of Palliative Medicine, Third Ed. Oxford: Oxford University Press, 2004, pp 316-341. |
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