This Page Intentionally Left Blank - Int Medical

NSAIDs and opioids 65
agent or another (perhaps from genetic variability), but the general equivalence
of the opioids is demonstrated by a wealth of data.
One caveat to the general rule of opioid equivalence is that mixed agonist–
antagonist agents have clinical characteristics that differ from those of the
pure mu receptor agonists. The agonist–antagonists can be associated with
more dysphoria and may precipitate withdrawal symptoms in patients who
are not opioid naïve. Unless there is a specific reason, we prefer use of
traditional pure mu agonists (e.g. morphine). (As a related point, the ED
provider should be wary of administration of naloxone to patients in whom
opioids may be necessary for analgesia; subsequent pain control can be
complicated by the difficulty of overcoming opioid reversal agents.)
The second caveat to considering opioid deals with the imprecision of
“opioid potency equivalence tables.” The case of hydromorphone, which can
be illustrated with high-quality data, serves well as an illustration of the
difficulty of arriving at an evidence-based level of “equipotency” compared
with morphine. A recent ED study found a dose of 0.015 mg/kg hydromorphone
to be equally efficacious to 0.1 mg/kg morphine. 16 The resulting
ratio of 15:1 markedly differs from what pain experts denote as the accepted
standard: 7:1. 17 The situation is further obfuscated by trial evidence suggesting
that, for PCA dosing, the hydromorphone:morphine potency ratio is roughly
3:1. 17 Confusion can be compounded when considering pediatric studies,
which demonstrate risk for hydromorphone underdosing when adult equipotency
data are applied in younger patients. 18 We do not recommend wholesale
distrust or abandonment of equianalgesia tables, but we do suggest that acute
care providers should not be dogmatic about applying such data.
The equianalgesia tables do provide an important opioid dosing starting
point, the utility of which is underlined by another tenet we wish to emphasize.
An opioid, like any other drug, ought to be given a fair trial in an
individual patient before concluding that it is not efficacious. All too frequently,
a few small doses of an opioid are given, then clinicians switch to a
second opioid because of “failure” of the initial agent. This practice represents
unnecessary polypharmacy. In the case of morphine, we have seen
countless instances where providers wish to switch to a second opioid
because of continuing pain after 10 mg (or less) – this switch despite the