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6. ADMINISTRATION OF SYSTEMIC
ANALGESIC DRUGS
Opioid and non‐opioid analgesic drugs can be administered systemically by a number of
different routes. The choice of route may be determined by various factors, including the
aetiology, severity, location and type of pain, the patient’s overall condition and the
characteristics of the chosen administration technique. Additional factors to consider with any
route of administration are ease of use, accessibility, speed of analgesic onset, reliability of
effect, duration of action, patient acceptability, cost, staff education and supervision available.
The principles of individualisation of dose and dosing intervals apply to the administration of
all analgesic agents, particularly opioids, by any route. A lack of flexibility in dose schedules has
often meant that intermittent and ‘prn’ (as needed) methods of pain relief have been
ineffective when the routes of administration discussed below have been used (Bandolier,
2003). Frequent assessment of the patient’s pain and their response to treatment (including
the occurrence of any side effects) rather than strict adherence to a given dosing regimen is
required if adequate analgesia is to be obtained.
The text in Sections 6.1 to 6.4 below relates to opioids, non‐selective non‐steroidal anti‐
inflammatory drugs (nsNSAIDs) and coxibs. For information about oral and parenteral routes
of administration of systemically administered adjuvant drugs, refer to Section 4.3.
CHAPTER 6 6.1 ORAL ROUTE
Oral administration of analgesic agents is simple, non‐invasive, has good efficacy in most
settings and high patient acceptability. Other than in the treatment of severe acute pain and
providing there are no contraindications to its use, it is the route of choice for the
administration of most analgesic drugs.
Limitations to the oral route include vomiting or delayed gastric emptying, when absorption is
likely to be impaired. If multiple doses of an oral analgesic drug are given before return of
normal gastric motility, accumulated doses may enter the small intestine at the same time
once emptying resumes (‘dumping effect’). This could result in an unexpectedly large systemic
uptake of the drug and an increased risk of adverse effects.
Rates of absorption will vary according to the formulation of the oral analgesic agent
(eg tablet, suspension, controlled‐release [CR] preparation). Bioavailability will also vary
between drugs because of the effects of first‐pass hepatic metabolism following uptake into
the portal circulation. Titration of pain relief with oral analgesic drugs is slower compared with
some of the other routes of administration discussed below.
Direct comparisons between oral opioid and non‐opioid analgesics, or between oral and other
routes of administration, are limited. Indirect comparisons, where the individual drugs have
been compared with a placebo, have been used to generate a ‘league table’ of analgesic
efficacy (see Table 6.1). This table is based on randomised, double‐blind, single‐dose studies
in patients with moderate to severe pain and shows the number of patients that need to be
given the active drug (NNT) to achieve at least 50% pain relief in one patient compared with
a placebo over a 4 to 6 hour treatment period (Moore et al, 2003).
The validity of this approach as a true method of comparison of drugs may be questioned as
there is no standardisation of the acute pain model or patient and only single doses of the
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