42 - Long-term treatment with capsaicin 8% patches: a subgroup analysis in patients with postherpetic neuralgia from an open-label study

¹NYU Langone Health, New York, NY, USA. ²Grünenthal GmbH, Aachen, Germany. 3Grünenthal Inc., Morristown, NJ, USA

Purpose
Painful neuropathy or peripheral neuropathic pain (PNP) is a common neurological condition estimated to affect ~7–8% of the general population in Europe. Managing patients with PNP is challenging; it often becomes chronic and can have a significant impact on quality of life. According to the revised International Association for the Study of Pain (IASP) recommendations for ICD11, PNP is considered to be a distinct chronic pain condition (Scholz et al., 2019).¹ Postherpetic neuralgia (PHN) following shingles infection, has specifically been named as one of the PNP conditions. High concentration 8% capsaicin patch (HCCP) is commonly recommended as a second line therapy for PHN. HCCP is indicated for the treatment of peripheral neuropathic pain (PNP) in the EU and for the treatment of neuropathic pain associated with postherpetic neuralgia (PHN) and for neuropathic pain associated with diabetic peripheral neuropathy (DPN) of the feet in the US. Capsaicin is a highly selective, potent and high-affinity exogenous agonist for the transient receptor potential cation channel subfamily V member 1 (TRPV1) receptors which, through a combination of activities, defunctionalizes nociceptor fibres and reduces cutaneous hypersensitivity. As a result, capsaicin is an attractive peripherally acting treatment to control localized pain, hyperalgesia, or allodynia (Anand and Bley, 2011).² The HCCP delivers the drug effectively and directly to the skin while limiting the risk of systemic effects and drug interactions. Whilst controlled trials have demonstrated the safety and effectiveness of capsaicin patches, the STRIDE study was designed to investigate the long-term safety of repeated patch administration in patients with non-diabetic neuropathic pain (Gálvez et al., 2017).³ The present analysis considers the effect on treatment outcomes among a subgroup of patients with PHN included in the STRIDE study.
Methods
The STRIDE study was an open-label, multicenter, 52-week observational trial conducted in Europe. A diagnosis of PHN was based on pain persisting since shingles vesicle crusting, for a minimum of 3 months. Prior treatment with capsaicin patches and a history of diabetes were among the exclusion criteria. Patients received up to 6 capsaicin 640 g/cm² (8% weight for weight) HCCP treatments at 9- to 12-week intervals. At each application visit, a maximum of 4 patches equivalent to an area of up to 1120 cm² were applied for 60 minutes. HCCP retreatment was at the investigator’s discretion and according to patient feedback. Long-term tolerability and safety were the primary objectives of the study. In addition, areas of spontaneous pain and allodynia were monitored, and various scales were used to assess pain, quality of life and overall treatment outcome at each retreatment assessment timepoint. Descriptive statistics (including means and standard deviations) are presented; missing observations were not imputed.
Results
Of the 107 PHN patients included in the study, 66 completed the trial. The reason for withdrawal was lack of efficacy (14.95%), adverse events in (4.67%) and other reasons (18.69%). HCCP was applied once in 22 patients, twice in 26, three times in 24 and ≥4 times in 35. All but 1 patient used preapplication topical anesthesia during the study, and 79.4% used concomitant medications for neuropathic pain.
73% of patients experienced possible or probable drug-related adverse events, mostly associated with transient application site reactions (57.9%). The maximum severity was mild or moderate in 57% of cases, and only 1 drug-related event required treatment discontinuation.
The average daily pain score was reduced from a baseline value of 6.6 (SD, 1.46) to 5.0 (1.99) after 6 months and 4.6 (2.18) after 12 months. The overall change in mean daily pain intensity by the end of study was approximately -1.7. The proportion of responders (≥30% decrease from baseline on a Numerical Pain Rating Scale) progressively increased during the study, to 22.7% after 3 months, and 33.3% and 39.7% after 6 and 12 months, respectively. Over 50% of patients showed at least minimal improvement according to the assessment of their condition by the end of study. The area of allodynia/hyperplasia and the extent of spontaneous pain (reported in most patients at baseline, mainly on the torso) decreased during the study by just over 20%.
Conclusions
HCCP repeat application over 12 months in patients with PHN was well tolerated, with mostly transient local adverse events directly linked to the site of application. Progressive and sustained reduction in pain intensity was achieved, as well as reductions in the area of allodynia and spontaneous pain. Overall, the findings from this study demonstrate that repeated HCCP application is a well-tolerated and effective long-term treatment option in patients with PHN.