Capsaicin patch safe, effective for long-term treatment of non-diabetic neuropathic pain
Capsaicin 8% patch shows potential as a long-term treatment option for non-diabetic patients with peripheral neuropathic pain, with a new study reporting that repeat treatment over 52 weeks is well tolerated, producing sustained reductions in average pain intensity with variable sensory function alteration and minimal chance of complete sensory loss.
The highly selective vanilloid receptor subtype 1 (TRPV1) agonist capsaicin triggers depolarisation of sensory afferents, producing a brief warming, burning, stinging or itching sensation.
“Exogenous agonists of TRPV1, such as capsaicin, are able to prolong this depolarisation, causing defunctionalisation of hyperactive nociceptors in the skin, leading to pain relief,” researchers said. “The capsaicin 8% patch delivers a high concentration of capsaicin directly into the skin to provide both acute and long-lasting pain relief.”
In the study, the application of up to six capsaicin 640 g/cm² (8 percent weight for weight) patch treatments at 9 to 12 week intervals over a 52-week period was well tolerated. The population comprised 306 patients—accounting for 107 who had post-herpetic neuralgia, 99 who had post-traumatic or post-surgical nerve injury, 80 who had HIV-associated distal sensory polyneuropathy (HIV-DSPN), and 20 who had other peripheral neuropathic pain. [J Clin Pain 2016; doi:10.1097/AJP.0000000000000473]
Treatment-emergent adverse events (TEAE) and drug-related TEAEs occurred in 82.4 and 67.6 percent of patients, respectively. Pain at the site of application was the most common drug-related TEAE (36.6 percent). There were no reports of serious drug-related TEAEs.
Sensory category shift analyses revealed that half of patients (50.4 percent) had a sensory deterioration/loss in at least one modality by study conclusion. Further, a few patients (1.1 to 3.6 percent; depending on modality) developed hyperaesthesia or allodynia. The number of patients who reported an improvement in a sensory modality post-treatment was between 25.2 and 32 percent.
In terms of efficacy, the treatment produced a sustained reduction in average pain intensity, with the average daily pain decreasing from 6.6 at baseline to 4.7 at month 12. The overall change in mean daily pain intensity during this period was -1.9 (95 percent CI, -2.19 to -1.59).
“As capsaicin causes defunctionalisation of hyperactive nociceptors, which leads to pain relief, impaired sensory perception may have been a potential effect of the patch following repeat treatment,” researchers explained.
“In addition, regenerating small diameter fibres may be sensitive and can therefore lead to unwanted cutaneous tenderness or frank pain. Indeed, both types of sensory changes were seen across all sensory modalities,” they continued.
They noted that the emergent hyperalgesia or allodynia reported in a minority of patients could be considered an unfortunate adverse effect, although the condition did not appear to have had an effect on the total pain of the patients.
Neuropathic pain is a common neurological condition that negatively affects health-related quality of life, particularly impairing physical, emotional and social functioning as well as sleep quality.
Given the findings, capsaicin 8% patch may be used to treat patients with peripheral neuropathic pain in the long term, researchers said. “[It has] minimal significant systemic absorption [which] limits the potential for drug-drug interactions or the need for dose adjustment in the elderly or patients with hepatic or renal impairment.”