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6.3 INTRAMUSCULAR AND SUBCUTANEOUS ROUTES

IM and SC injections of analgesic agents (usually opioids) are still commonly employed for the
treatment of moderate or severe pain. Absorption may be impaired in conditions of poor
perfusion (eg in hypovolaemia, shock, hypothermia or immobility), leading to inadequate early
analgesia and late absorption of the drug depot when perfusion is restored.
6.3.1 Opioids and tramadol

IM injection of opioids has been the traditional mainstay of postoperative pain management,
despite the fact that surveys have repeatedly shown that pain relief with prn IM opioids is
frequently inadequate. Although IM opioids are often perceived to be safer than opioids given
by other parenteral routes, the incidence of respiratory depression reported in a review
ranged from 0.8 (0.2 to 2.5)% to 37.0 (22.6 to 45.9)% using respiratory rate and oxygen
saturation, respectively, as indicators (for comparisons with PCA and epidural analgesia,
see Section 7; for comments on respiratory rate as an unreliable indicator of respiratory
depression, see Section 4.1.3) (Cashman & Dolin, 2004 Level IV).
Single doses of IM morphine 10 mg (McQuay et al, 1999 Level I) and IM pethidine (meperidine)
100 mg (Smith et al, 2000 Level I) have been shown to be effective in the initial treatment of
moderate to severe postoperative pain.
The use of an algorithm allowing administration of IM morphine or pethidine hourly prn and
requiring frequent assessments of pain and sedation, led to significant improvements in pain
relief compared with longer dose interval prn regimens (Gould et al, 1992 Level III‐3).
The quality of pain relief was less with intermittent IM regimens compared with IV PCA
(Hudcova et al, 2005 Level I).
The placement of SC plastic cannulae or ‘butterfly’ needles allows the use of intermittent CHAPTER 6
injections without repeated skin punctures. In healthy volunteers, median time to reach
maximum serum concentration (T max) after SC injection of morphine was 15 mins (Stuart‐Harris
et al, 2000). In elderly adults, mean T max after a single SC injection of morphine was
15.9 minutes and the rate of absorption and the variability in the rate of absorption were
similar to those reported after IM injection (Semple et al, 1997 Level IV). In patients given a
second and same dose of SC morphine 5 hours after the first, it was shown that there can
also be significant within‐patient variations in absorption (Upton et al, 2006).
In children, there was no difference in rate of onset, analgesic effect and side effects when
SC injections of morphine were compared with IM morphine injections, and there was a
significantly higher patient preference for the SC route (Cooper, 1996 Level II; Lamacraft et al,
1997 Level IV). A comparison of IM and SC morphine in patients after Caesarean section
reported no significant differences in side effects, patient satisfaction or pain relief at rest,
but lower pain scores after SC administration at 12, 16 and 20 hours after surgery (Safavi &
Honarmand, 2007 Level II).
A comparison of the same dose of morphine given as either a single SC or IV injection, showed
that use of the IV route resulted in more rapid onset of analgesia (5 minutes IV; 20 minutes SC)
and better pain relief between 5 minutes and 25 minutes after injection, but also led to higher
sedation scores up to 30 minutes after injection, and higher PCO 2 levels (Tveita et al, 2008
Level II). However, a comparison of intermittent IV and SC doses of hydromorphone (the
doses adjusted in a similar manner according to the patients’ pain scores and given at intervals
of no less that 3 hours) showed no differences in pain relief or side effects over a 48‐hour

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