PAIN MANAGEMENT IN ACUTE PORPHYRIA
When treating pain in this group one is dealing
with patients with high disease activity and
therefore at maximum risk of inadvertently worsening
an acute attack.
The principle therefore is:
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to choose
a drug which is definitely known to be safe
as demonstrated by repeated use in this
group of patients and
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a drug which fulfils
the optimum characteristics for the clinical
situation, e.g. rapid onset of action, lack
of side effects. Pain management is a major
aspect of the clinical management of acute
porphyria, and there is therefore extensive
clinical experience on the use of certain
analgesics. Safe alternatives exist for
all classes of analgesic drugs and a list
based on the experiences of several porphyria
groups is included at the end of this article. |
I. MANAGEMENT OF PAIN DURING
AN ACUTE ATTACK
Opiates are the analgesics of choice as they
can be given intravenously, subcutaneously or
intramuscularly which ensures onset of action
is rapid. When used as a continuous infusion,
usually via a syringe driver, the amount of
opiate can be adjusted to the needs of the patient
and in many cases can be controlled by the patients
themselves. There is wide clinical experience
with the safe use of morphine and pethidine,
which should be the first choice in this group
of patients. Although reported as safe, there
has been less experience with the use of fentanyl
and alfentanyl. There appears to be little
justification for the use of oral or transdermal
opiate analgesia (patches) in this group of
patients, as onset of action is slow and only
reaches a maximum effect after 12 hours.
One of the main side effects of all opiate-based
painkillers is nausea, which may also be a symptom
of acute porphyria. Effective treatment with
an anti-emetic is essential during an acute
attack and experience has shown that prochlorperazine,
domperidone and cyclizine are safe.
II. MANAGEMENT OF PAIN
BETWEEN ACUTE ATTACKS
It should not always be assumed that abdominal
or other pain is always due to the porphyria and
a careful history to find out whether the nature
of the pain has changed can help to determine
this. Patients with acute porphyria are also at
risk of common causes of abdominal pain, which
may require specific treatment.
It is vital that regular use of opiate analgesia
in between acute attacks be avoided if at all
possible to avoid opiate dependence. It is hoped
that all patients with porphyria will ultimately
experience a decrease in disease activity, which
will allow them to lead a normal life, and this
should include absence of dependence on opiates.
Patients should therefore be encouraged to use
simple measures to control their pain such as
oral paracetamol or a safe non-steroidal anti-inflammatory
(NSAID) such as aspirin or ibuprofen. Other safe
alternative NSAID's are listed below.
A small minority of patients experience chronic
neuropathic pain which may be present almost continuously.
Where analgesia with a NSAID has failed to control
pain, and the pain is assumed to be neuropathic
in origin adjunct therapy with a safe drug may
be tried. Of the drugs used for this purpose,
gabapentin and amitriptyline appear to be safe.
However as these patients have particularly active
disease they should be carefully monitored during
treatment.
Safe analgesics
| Opiates
analgesics : |
Morphine, pethidine, alfentanil,
fentanyl, dihydrocodeine |
| Non-opiate
analgesics : |
Aspirin, ibuprofen, paracetamol (per
os), naproxen, indomethacin, fenbufen |
| Anti-emetics
: |
Prochlorperazine, domperidone
(usually given with opiates) |
| Adjunct
drugs : |
Amitryptiline |
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