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In general, there is no good evidence that nsNSAIDs given parenterally or rectally are more
effective, or result in fewer side effects, than the same drug given orally for the treatment of
postoperative pain (Tramer et al, 1998 Level I). Only in the treatment of renal colic do IV
nsNSAIDs result in more rapid analgesia (Tramer et al, 1998 Level I).

6.1.3 Paracetamol
Paracetamol is an effective analgesic for acute pain (Toms et al 2008 Level I; Toms et al, 2009 Level
I; Weil et al, 2007 Level I). However, as noted above, the effects of different analgesics may vary
with different pain models (Oscier & Milner, 2009). In a re‐analysis of data available for
paracetamol, it was found to be significantly less effective for pain relief after orthopaedic
than after dental procedures (Gray et al, 2005 Level I).
The oral bioavailability of paracetamol is good at between 63% and 89% (Oscier & Milner, 2009).
However, early postoperative oral administration can result in plasma concentrations that can
vary enormously after the same dose and may remain subtherapeutic in some patients (Holmer
Pettersson et al, 2004 Level II).
In the same doses, orally administered paracetamol was less effective and of slower onset
than paracetamol given by IV injection, but more effective and of faster onset than
paracetamol administered by the rectal route (see below).
Paracetamol effervescent tablets were absorbed significantly faster than ordinary paracetamol
(Rygnestad et al, 2000 Level II).

6.2 INTRAVENOUS ROUTE

Analgesic drugs given by the IV route have a more rapid onset of action compared with most
other routes of administration. CHAPTER 6

6.2.1 Opioids and tramadol
Intermittent intravenous bolus doses
Titration of opioids for severe acute pain is best achieved using intermittent IV bolus doses as
it allows more rapid titration of effect and avoids the uncertainty of drug absorption by other
routes. The optimal doses and dose intervals for this technique have not yet been established.
In a postoperative care unit, 2 mg or 3 mg bolus doses of morphine given at 5‐minute dose
intervals as needed and with no limitation on the number of bolus doses administered, was
more effective and resulted in no greater incidence of side effects than the same doses given
at 10‐minute intervals or when a maximum of 5 doses only was allowed (Aubrun et al, 2001
Level III‐3). In a comparison of IV fentanyl and morphine bolus doses every 5 minutes as
needed for prehospital analgesia over a period of just 30 minutes, no difference was found in
pain relief or incidence of side effects (Galinski et al, 2005 Level II).
Titration of IV bolus doses of an opioid is frequently accomplished using a treatment algorithm
to guide management, which includes age‐based bolus doses of opioid given at 3‐ or 5‐minute
intervals as needed (Macintyre & Schug, 2007).
IV tramadol was found to be more effective than the same dose given orally after dental
surgery; however it was recognised that the difference in bioavailabilty of a single dose of
tramadol may be up to 30% (Ong et al, 2005 Level II).

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