People suffering CRPS commonly apply topical agents as part of their wider daily drug regime. This is despite allodynia inevitably making application difficult.
Topical vs Transdermal
The terms ‘topical’ and ‘transdermal’ are often used interchangeably, but it is important to differentiate between the two. Both refer to medication applied to the skin, but whereas ‘topical’ medications absorb passively into the skin producing a localised effect in and immediately around the area where they are applied, ‘transdermal’ medications incorporate compounds or technology to enhance skin penetration. In that way they increase the amount of the drug that crosses the skin barrier to the extent that the drug can then be circulated to, and affect, other areas of the body.
Examples of drugs delivered transdermally for CRPS include Fentanyl and Clonidine. Perhaps the most common examples of drugs applied topically for the condition are Lidocaine and Capsaicin.
Compound Analgesic Cream
Back in 2015, researchers at the University of Newcastle in Australia published a paper in the journal Pain Practice on the outcome of a small-scale trial of a multi-compound topical cream for treating early stage CRPS. The trial followed a study which suggested that a topical combination cream reduced allodynia in rats.
The authors of the study said that “Driven by these findings, we assessed the outcomes of CRPS patients treated with a compound analgesic cream (CAC) consisting of ketamine 10%, pentoxifylline 6%, clonidine 0.2%, and dimethyl sulfoxide 6% to 10%.”
The trial involved only 13 patients but 9 of them reported a moderate reduction in pain after using the CAC. “Six patients reported sustained benefits after 2 months of CAC use, and 2 patients reported complete resolution of pain/symptoms: one had early CRPS-I and the other received a partial CRPS diagnosis. An otherwise medication refractory and intolerant patient found partial benefit with the CAC.”
The limited number of people involved in this trial means that the results should be treated with great caution. And of course, statistically, a significant proportion of people with early stage CRPS achieve remission in any event.
In fairness to the authors, they went only so far as to conclude that “These results demonstrate promise for this topical combination as a useful treatment in multimodal therapy for patients with CRPS, with the potential to resolve pain/symptoms in early CRPS patients.”
What is somewhat puzzling is that despite this “promise” and “potential“, in four years since publication, no further trials have materialised.