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To the Editor:

We note with interest Dr. Mercadante's experience in the multifaceted nature of pain in patients on dialysis. No doubt our patient's pain could have been exacerbated by many factors, including the enforced confinement of dialysis and his inability to smoke during a session. We cannot prove our hypothesis that his fentanyl was removed by dialysis in the absence of serum fentanyl levels, but report strong anecdotal evidence of pain exacerbation following dialysis of a patient on transdermal fentanyl. Both the patient and his wife commented on this frequently and came to dread dialysis because of the predictable exacerbation of his pain immediately after. Indeed, this pattern was continued when the patient was changed from transdermal fentanyl to a subcutaneous infusion of sufentanil.

This case did not have the characteristics of opioid-induced hyperalgesia on two accounts. First, the increasing pain experienced by our patient over time was completely consistent with the relentless progression of his metastatic disease. Secondly, his pain control was often well controlled on the day prior to dialysis. Toward the end of his life, the clinical picture was complicated by many things, including emotional distress, polypharmacy, comorbidity, and his reluctance to stay in hospital because of his wish to use recreational drugs at home. It would be difficult to attribute his distress to a single factor, such as opioid-induced hyperalgesia.

The issue regarding dialyzate filters deserves further investigation. The system used in our patient was a Fresenius F10 HPS low flux 2.4 polysulphone membrane. We would be interested to know of the experience of other clinicians using this system in maintaining pain control in patients on dialysis. As has been referenced,¹ it is possible that fentanyl is dialyzable by some membranes but not others.

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Reference 

1. Joh J, Sila MK, Bastani B. Nondialyzability of fentanyl with high-efficiency and high-flux membranes. [Letter] Anesth Analg. 1998;86:447
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