Topical Morphine – An Experimental Approach to Chronic Pain

Practitioners who treat patients with chronic pain understand just how difficult management of that population can be. As of today, the evaluation of pain remains completely subjective; no lab tests or imaging studies can provide any meaningful insight into how much pain a patient feels. When the pain is severe and intractable, the only option becomes opioid analgesics, which have high potential for abuse and are laden with side effects ranging from constipation and sedation to respiratory depression, testosterone deficiency, and immuno-modulation. The trouble with opioids is that they must be ingested in an oral form with systemic absorption regardless of where the actual pain lies. Over the past few years, a quiet murmur has been rippling through the pain practitioner community about the possibility of dispensing morphine as a topical agent. Small scale clinical trials and animal models have shown some promise, and also raised some questions about this experimental approach.

Converting systemic agents to topical agents is not a new phenomenon. A few topical agents already exist for the treatment of pain. For example, aspirin-type products exist in topical form as a cream which is available over the counter. Similarly, topical capsaicin cream and gel is commercially available for the treatment of pain. In the prescription category, there has been recent approval of topical lidocaine (same as the novocaine used for dental anesthesia) for the use of chronic pain associated with diabetic peripheral neuropathy and post-herpetic neuralgia (also known as shingles). More recently, there has been FDA approval for topical diclofenac, an anti-inflammatory similar to ibuprofen, as both a patch and a gel for acute musculo-skeletal conditions and pain associated with arthritis.

In a recent issue of Practical Pain Management, a journal for pain practitioners, Dr. Forest Tennant detailed his practice-based clinical trial on a homemade formulation of topical morphine for patients who had failed all other management. The physician simply crushed up immediate-release morphine tablets and mixed it into a moisturizing cold cream which the patient supplied. The patients were instructed to apply the cream to painful areas as needed. For his observation study, he noted that almost all patients noted significant relief of their pain symptoms, which lasted for hours. Their side effects were negligible. It’s important to bear in mind that these are patients who had severe pain which failed to respond to any other conventional treatment. Results of this magnitude are profound in such a refractory population.

Not all the reviews have been positive, however. Some animal models have shown that topical morphine used on painful skin ulcers are associated with delayed wound healing. Also, while topical diclofenac shows 1-6% systemic absorption of medication depending on preparation, there are no convincing studies as of yet to measure how much topical morphine makes its way into the bloodstream. If that number is too high, then patients run the risk of all the adverse effects associated with opioids. Regardless, for patients with intractable pain limited to small areas, topical morphine holds promise as a useful agent when all else has failed.

References

Tennant, F. Topical Use of Morphine. Practical Pain Management. October 2008.

Rook JM, Hasan W, McCarson KE (2008). Temporal effects of topical morphine application on cutaneous wound healing. Anesthesiology, 109 (1), 130-136.