Topical analgesics

A clinical and mechanistic study of topical borneol-induced analgesia

Bingpian is a time‐honored herb in traditional Chinese medicine (TCM). It is an almost pure chemical with a chemical composition of (+)‐borneol and has been historically used as a topical analgesic for millennia. However, the clinical efficacy of topical borneol lacks stringent evidence‐based clinical studies and verifiable scientific mechanism. We examined the analgesic efficacy of topical borneol in a randomized, double‐blind, placebo‐controlled clinical study involving 122 patients with postoperative pain. Topical application of borneol led to significantly greater pain relief than placebo did. Using mouse models of pain, we identified the TRPM8 channel as a molecular target of borneol and showed that topical borneol‐induced analgesia was almost exclusively mediated by TRPM8, and involved a downstream glutamatergic mechanism in the spinal cord. Investigation of the actions of topical borneol and menthol revealed mechanistic differences between borneol‐ and menthol‐induced analgesia and indicated that borneol exhibits advantages over menthol as a topical analgesic. Our work demonstrates that borneol, which is currently approved by the US FDA to be used only as a flavoring substance or adjuvant in food, is an effective topical pain reliever in humans and reveals a key part of the molecular mechanism underlying its analgesic effect.

Evaluation of the Percutaneous Absorption of Ketamine HCl, Gabapentin, Clonidine HCl, and Baclofen, in Compounded Transdermal Pain Formulations, Using the Franz Finite Dose Model

Objective. This study evaluates the ability of four commonly used analgesics (ketamine HCl, gabapentin, clonidine HCl, and baclofen), when incorporated into two transdermal compounding bases, Lipoderm and Lipoderm ActiveMax, to penetrate human cadaver trunk skin in vitro , using the Franz finite dose model.

Design. In vitro experimental study .

Methods. Ketamine HCl 5% w/w, gabapentin 10% w/w, clonidine HCl 0.2% w/w, and baclofen 2% w/w were compounded into two transdermal bases, Lipoderm and Lipoderm ActiveMax. Each compounded drug formulation was tested on skin from three different donors and three replicate skin sections per donor. The Franz finite dose model was used in this study to evaluate the percutaneous absorption and distribution of drugs within each formulation.

Results. Rapid penetration to peak flux was detected for gabapentin and baclofen at approximately 1 hour after application. Clonidine HCl also had a rapid penetration to peak flux occurring approximately 1 hour after application and had a secondary peak at approximately 40 hours. Ketamine HCl exhibited higher overall absorption rates than the other drugs, and peaked at 6–10 hours. Similar patterns of drug distribution within the skin were also observed using both transdermal bases.

Conclusions. This study suggests that the combination of these 4 analgesic drugs can be successfully delivered transdermally, using either Lipoderm or Lipoderm ActiveMax. Compounded transdermal drug preparations may then provide physicians with an alternative to traditional oral pain management regimens that can be personalized to the specific patient with the potential for enhanced pain control.

Visualizing dermal permeation of sodium channel modulators by mass spectrometric imaging

Determining permeability of a given compound through human skin is a principal challenge owing to the highly complex nature of dermal tissue. We describe the application of an ambient mass spectrometry imaging method for visualizing skin penetration of sodium channel modulators, including novel synthetic analogs of natural neurotoxic alkaloids, topically applied ex vivo to human skin. Our simple and label-free approach enables successful mapping of the transverse and lateral diffusion of small molecules having different physicochemical properties without the need for extensive sample preparation.

Use of topical medication in orofacial neuropathic pain: a retrospective study

OBJECTIVE

The objective of this study was to evaluate the effect of topical medications as a single treatment or in combination with systemic medications in the treatment of orofacial neuropathic pain conditions.

STUDY DESIGN

A retrospective chart review of 39 patients treated for orofacial neuropathic pain at the Orofacial Pain Clinic in the New Jersey Dental School was performed. In line with the treatment selection, the subjects were divided into 3 groups: topical medications only (n = 12), systemic medications only (n = 10), and a combination of both (n = 17).

RESULTS

The starting pain level as expressed in pain Visual Analog Scale for the 3 groups was significantly different. The combined treatment group baseline pain level (7.5 +/- 0.403 SEM; P = .0015) and the systemic treatment only group pain level (8.6 +/- 0.611 SEM; P = .0375) was significantly elevated compared to the topical only group (6.1 +/- 0.716 SEM; P = .1057). Following treatment, pain level was significantly reduced in all 3 groups. The combined group had the highest pain relief (52.0 +/- 6.676 SEM % reduction; P < .0001) followed by the systemic-only group (40.6 +/- 9.727 SEM % reduction; P = .0029) and the topicals-only group (40.9 +/- 10.775 SEM% reduction; P = .0048). The time taken for the topical treatment only to act was significantly shorter (3 weeks +/- 0.479 SEM; P = .0015) when compared with the systemic-only (4 weeks +/- 0.772 SEM; P = .3629) and the combined group (5.5 weeks +/- 0.912 SEM; P = .1738).

CONCLUSION

Topical medication as single treatment or in combination with systemic medications can reduce orofacial neuropathic pain severity. Further prospective research should be performed to validate this treatment option.

Pharmacological pain management in the elderly patient

With the increasing number of elderly patients the issue of pain management for older people is of increasing relevance. The alterations with aging of the neurobiology of pain have impacts of pain threshold, tolerance and treatment. In this review the available evidence from animal and human experimentation is discussed to highlight the differences between young and older subjects along with consideration of how these changes have practical effect on drug treatment of pain. Cognitive impairment, physical disability and social isolation can also impact on the accessibility of treatment and have to be considered along with the biological changes with ageing. Conventional pain therapies, while verified in younger adults cannot be automatically applied to the elderly without consideration of all these factors and in no other group of patients is a holistic approach to treatment more important.