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Large IV bolus doses of tramadol can result in a high incidence of emetic symptoms. This effect
can be reduced by slowing delivery of the drug or, in the surgical setting, by giving it before
the patient emerges from general anaesthesia (Pang et al, 2000 Level II).
Continuous infusions
A continuous infusion of opioids results in constant blood levels after approximately 4 half‐
lives of the opioid used. The aim of an infusion is to avoid the problems associated with the
peaks and troughs of intermittent administration techniques. However, the variation in patient
response, the changing intensity of acute pain with time and the delay between any alteration
of the infusion rate and its subsequent effect, may result in inadequate treatment of incident
pain or delayed onset of side effects, such as respiratory depression. Very close monitoring is
therefore essential with continuous infusions of opioids.
Compared with PCA, continuous IV opioid infusions in a general ward setting resulted in a
5‐fold increase in the incidence of respiratory depression (Schug & Torrie, 1993 Level IV).
6.2.2 Non-selective non-steroidal anti-inflammatory drugs
and coxibs
There are only a limited number of nsNSAIDs or coxibs available for IV injection at present and
fewer still where Level I evidence for individual efficacy is available. In single doses as the sole
analgesic agent, the coxib parecoxib IV 20 to 40 mg has been shown to be effective (Lloyd et al,
2009 Level I).
The formulation of drug used may affect efficacy. Comparison of a polyethylene glycol and
benzyl alcohol (PG‐BA) diclofenac solution with one that used hydroxypropyl beta‐cyclodextrin
CHAPTER 6 more rapid onset of analgesia (Leeson et al, 2007 Level II). The incidence of moderate to severe,
(HPβCD) to solubilise diclofenac in a small volume showed that IV HPβCD diclofenac resulted in

but not mild thrombophlebitis may be less with IV diclofenac (Colucci et al, 2009).
In most cases the route of administration does not seem to alter efficacy. IV nsNSAIDs or
coxibs are more expensive than oral or rectal nsNSAIDs although their efficacy and likelihood
of side effects is similar (Tramer et al, 1998 Level I). A more recent comparison of rectal
diclofenac and IV parecoxib showed no difference in pain relief, side effects or rescue
analgesic requirements (Ng et al, 2008 Level II). Efficacy and times to onset of analgesia were
similar with IV and IM parecoxib (Daniels et al, 2001 Level II).
For renal colic, the onset of action of NSAIDs was faster when given IV compared with IM, oral
or rectal administration (Tramer et al, 1998 Level I).

6.2.3 Paracetamol
IV paracetamol was an effective analgesic after surgery (Sinatra et al, 2005 Level II). It was of
faster onset than the same dose given orally (Moller, Sindet‐Pedersen et al, 2005 Level II) but, as
with IV NSAIDs, it is more expensive.
While of equal analgesic efficacy, the incidence of local pain at the infusion site was
significantly less after IV paracetamol compared with the prodrug propacetamol (Moller, Juhl et
al, 2005 Level II).
Due to the good bioavailability and tolerability of oral paracetamol, the use of the IV form
should be limited to clinical circumstances where use of the enteral route is not appropriate.

156 Acute Pain Management: Scientific Evidence