The use of high dose topical capsaicin in the management of peripheral neuropathy: narrative review and local experience

The multicomponent Passerini reaction as a means of accessing diversity in structure, activity and properties: Soft and hard vanilloid/cannabinoid modulators

A growing body of evidence points to the existence of a crosstalk between the endovanilloid (EV)- and the endocannabinoid (EC) systems, leading to the concept of a single system based on a shared set of endogenous ligands and regulation mechanisms. The EV/EC system encompasses the ion channel TRPV1, the G protein coupled receptors CB1 and CB2, their endogenous ligands and the enzymes for biosynthesis and inactivation. Disorders in which the EV/EC interaction is involved are inflammation, pain, neurodegenerative diseases and disorders of bones and skin. In the present paper, with the aim of targeting the EV/EC system, the Passerini reaction is used in a diversity-oriented approach to generate a series of α-acyloxycarboxamides bearing different substructures that resemble endogenous ligands. Compounds have been screened for activity on TRPV1, CB1 and CB2 and metabolic stability in skin cells, liver subcellular fractions and plasma. This protocol allowed to generate agents characterized by a diverse activity on TRPV1, CB1 and CB2, as well as heterogeneous metabolic stability that could allow different routes of administration, from soft drugs for topical treatment of skin diseases to hard drugs for systemic use in inflammation and pain. Compared to natural mediators, these compounds have a better drug-likeness. Among them, 41 stands out as an agonist endowed with a well-balanced activity on both TRPV1 and CB2, high selectivity over TRPM8, TRPA1 and CB1, metabolic stability and synthetic accessibility.

Capsaicin-Loaded Melanin Nanoparticles for Long-Lasting Nociceptive-Selective Nerve Blockade

Clinically used amino-ester and amino-amide local anesthetics, such as bupivacaine and lidocaine, face two primary challenges: inadequate duration of action and nonselective action on both sensory and motor neurons, resulting in motor function loss alongside pain relief. In this work, we developed capsaicin-loaded melanin nanoparticles (Cap-MNPs) to address these two challenges. Capsaicin selectively acts on sensory neurons without affecting motor neurons, thereby achieving nociceptive-selective nerve blockade. Melanin is known for its exceptional biocompatibility, biodegradability, and abundance in pigmented human tissue. Melanin's inherent chemical structure and hydrophobic nature enable the encapsulation and sustained release of amino-ester and amino-amide local anesthetics with aromatic rings through π-π interactions and hydrophobic interactions. The drug loading efficiency of Cap-MNPs was 82.99 ± 1.55%, the drug loading capacity was 67.47 ± 4.24%, and capsaicin was continuously released for more than 360 h. In rats, a single injection of Cap-MNPs containing 8.04 mg of capsaicin produced a sciatic sensory nerve block lasting for 6 h without causing any local toxicity and capsaicin-related systemic toxicity. Cap-MNPs show promise as clinically useful therapeutics for pain management.

The role of the capsaicin 8% patch in the treatment of painful diabetic peripheral neuropathy

Treatment of painful diabetic peripheral neuropathy (PDPN) is challenging and often limited by drug tolerability and adverse effects. This review article focuses on the high-dose (8%) capsaicin patch that allows for improved efficacy and reduced application frequency in comparison to low-dose capsaicin formulations. Systemic absorption is minimal resulting in fewer systemic side effects than first-line oral medications. There is evidence that capsaicin patch treatment is well-tolerated, safe and provides effective pain relief maintained for several weeks; well-powered studies are needed to confirm these findings. The capsaicin 8% patch may benefit patients at high risk for adverse effects from oral medication, polypharmacy or inadequate pain relief from first-line therapies.

Scoping Review of Off-Label Topical Analgesia in Palliative, Hospice and Cancer Care: Towards Flexibility in Evidence-Based Medicine

Purpose

Scoping reviews address the nature of the literature per se rather than inferring evidence-based treatment guidelines. Scoping reviews of the published literature are intended to describe the aggregated nature of the evidence surrounding some agent or intervention, in contrast to systematic reviews that seek when possible to guide clinical practice. We conducted a scoping review to identify reports of potential clinical utility of off-label topical analgesics and adjuvants when FDA-approved treatments have proven inadequate.

Methods

We performed a comprehensive search of three databases (PubMed, Web of Science and Embase) for articles dating from 1947 to the present. Mindful that FDA-approved and WHO-recommended analgesic medications often prove inadequate for individual patients in extremis with palliative, hospice or cancer pain, we used broad, structured inclusion criteria to retrieve articles.

Results

We retrieved 12,100 articles; after screening, we had 39 reports addressing 19 different topical agents out of the 32 chemical entities. Our scoping review disclosed evidence about agents that might not have met inclusion criteria for clinical practice guidelines.

Discussion

Although generally considered lower quality evidence, case reports or series present suggestions for diverse topical medications to manage pain in challenging circumstances when high-quality evidence for agents and routes of administration is lacking.

Conclusion

Patients with the greatest need for evidence to identify and guide lesser-used agents during aggressive pain management are the most difficult to enroll and follow in standardized, controlled and/or blinded clinical trials. This scoping review identifies medications, dosages, and routes of topical agents reported to be effective in these often-challenging circumstances. Until larger and higher quality studies are completed, we must rely on the best available evidence even if of lower quality.