What types of pain can occur and which treatments are most suitable?
Drugs
Nociceptive pain
Neuropathic pain
pain may be mixed nociceptive/neuropathic
paracetamol
effective; most useful when taken regularly at maximal
recommended doses (negligible anti-inflammatory
effect)
less effective
opioids
effective
may be effective (depends on choice
and dose)
NSAIDs
effective (useful anti-inflammatory effects)
less effective
TCAs, parenteral local
anaesthetics, antiepileptics,
clonidine
rarely used
may be effective (TCAs and
antiepileptics are the treatments of
choice)
What long term issues may occur with chronic opioid use?
Most specialists in pain medicine agree that patients on opioids will always develop physical
dependence, will sometimes develop tolerance, but will rarely develop addictive disorders.
The actual risk is unknown, and will vary depending on many factors including genetic factors,
personality and psychiatric disorders, and the pharmacological and physicochemical properties of
the drug prescribed.
Patients need clarification and reassurance about what these terms mean and what to expect when
taking opioids long term.
Physical dependence is an ‘adaptation’ process, where the body becomes reliant on the externally
provided opioid. The patient will develop a ‘drug class–specific withdrawal syndrome’ if they cease
the opioid medication suddenly, or reduce the dose rapidly, or are administered an antagonist. The
time to onset will depend on the half-life of the opioid ceased. For methadone, withdrawal
symptoms can present from three days after cessation, and last as long as 21 days. Features of
withdrawal syndrome are shown in Box 1.3.
Ceasing the opioids slowly over several weeks to months (depending on the drug and the dose) can
prevent withdrawal symptoms. Safe reduction rates are about 10% of the dose, weekly. Patients and
their doctors often consider withdrawal symptoms as an indication of addiction, but withdrawal is
purely a physiological response to lack of drug (see Drug addiction below).
Tolerance is an adaptation process, in which exposure to the drug induces changes that diminish the
drug’s effects. Over time the patient will require increasing doses of the drug, or the same dose
more frequently, to have the same effect. These increases need to be carefully considered and
discussed. High doses of opioids can cause their own problems, so most chronic pain specialists have
maximum doses with which they feel comfortable based on clinical experience—morphine 180
mg/day, oxycodone 120 mg/day, and methadone 60 mg/day are considered reasonable maximum
daily doses.
Tolerance is felt to be less likely with long-acting opioid preparations.
An adaptation occurs to all opioid therapeutic and adverse effects, but at different rates—and
adaptation to constipation occurs last (see Table 1.5).
Drug addiction is a chronic neuropsychobiological disorder, with genetic, psychosocial and
environmental factors influencing its development and manifestation. It is characterised by aberrant
drug-seeking and drug-taking behaviours that can include cravings, compulsive use, impaired control
over drug use, and continued use despite harm.
What was the total daily dose of Michael’s documented opioid consumption?
Drug
Endone 15mg
Codeine 12.8
Codeine 30
Frequency
5
4
2
Opioid dose
75 mg
51.2 mg
60 mg
186 mg
Equianalgesic
When changing opioid, start at 50% of the approximate equianalgesic dose; then titrate according to
response (see alsoEquianalgesic dosing).
Approximate dose
equivalent to 10 mg
IM/SC morphine1
Approximate
duration of action
(hours)2
Comments
codeine3 (analgesic only)
120–130 mg SC/IM;
200 mg oral
3–4
mild-to-moderate pain
dextropropoxyphene3
unknown
4–6
mild-to-moderate pain; not
recommended
fentanyl
100–150 mcg SC
0.5–1
moderate-to-severe acute or
chronic pain; preferred in renal
impairment
hydromorphone3
1.5–2 mg SC/IM;
6–7.5 mg oral
2–4; 24 (controlled release)
moderate-to-severe acute or
chronic pain
methadone (analgesic
only)
10 mg SC/IM;
20 mg oral4
8–24 (chronic dosing)
severe chronic pain
morphine3
30 mg oral
2–3; 12–24 (controlled
release)
moderate-to-severe acute or
chronic pain
Drug
Agonists
Drug
Approximate dose
equivalent to 10 mg
IM/SC morphine1
Approximate
duration of action
(hours)2
Comments
oxycodone
15–20 mg oral
3–4; 12–24 (controlled
release)
moderate-to-severe acute or
chronic pain
pethidine3
75–100 mg IM
2–3
not recommended
tramadol3
100–120 mg IM/IV;
150 mg oral
3–6; 12–24 (controlled
release)
moderate-to-severe pain
0.4 mg IM;
0.8 mg sublingual
6–8
not first line for analgesia
Partial agonists
buprenorphine(analgesic
only)
Compare and contrast the opioid pain patches marketed in Australia
Norspan (buprenorphine)
Partial agonist
High affinity for opiod
receptors
Prolonged onset and duration
of action
Takes 3 days to reach ss
Not first line for analgesia
20 ug/hr is patch is
approximately equivalrent to
100-150 mg/day of oral
tramadol OR 36 mg/day of oral
morphine
20 ug/hr patch is LESS potent
than the LOWEST strength
fentanyl patch (12 ug/hr)
Adapted from AMH 2011
Durogesic (Fentanyl)
Patch is efctive for 72 hoursf
Takes 24-72 hrs to reach
maximum effect, ss may not be
reached until the second patch
is applied.
Moderate to severe acute pain
or chronic pain
12 ug/hr patch is
approxiametely equivalent to
45 mg/day oral morphine