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:
|to choose a drug which is definitely known to be safe as demonstrated by repeated use in this group of patients and|
|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.|
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.
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.