Study to determine the efficacy of topical morphine on painful chronic skin ulcers

Topical opioid use in dermatologic disease: A systematic review

Topical opioid formulations offer a potential solution to manage pain and decrease the use of systemic opioids. Synthesis of use and efficacy of topical opioids in dermatological conditions has not been well characterized. We conducted a systematic search of the PubMed, Embase, and Cochrane databases from 1980 to February 2021. This study analyzed data from 14 articles and 263 patients on the use of topical opioids for pain related to chronic ulcers, burns, oral lichen planus, photodynamic therapy, and split-thickness skin grafts. Topical opioids included in this review were topical morphine and diamorphine. Common formulations consisted of 0.2-10 mg of opioid compounded with hydrogel or IntraSite gel. Topical opioids were variably effective in the use for pain control related to chronic ulcers and other dermatologic conditions. For example, the use of topical opioids appears to be effective in the reduction of pain related to pressure ulcers. Topical opioids were generally well tolerated. Insufficient data exist to adequately evaluate the efficacy and safety of topical opioid use in the context of nonpressure ulcers, burns, oral lichen planus, photodynamic therapy, and split-thickness skin grafts.

Dressings and topical agents for treating pressure ulcers

BACKGROUND

Pressure ulcers, also known as bedsores, decubitus ulcers and pressure injuries, are localised areas of injury to the skin or the underlying tissue, or both. Dressings are widely used to treat pressure ulcers and promote healing, and there are many options to choose from including alginate, hydrocolloid and protease-modulating dressings. Topical agents have also been used as alternatives to dressings in order to promote healing.A clear and current overview of all the evidence is required to facilitate decision-making regarding the use of dressings or topical agents for the treatment of pressure ulcers. Such a review would ideally help people with pressure ulcers and health professionals assess the best treatment options. This review is a network meta-analysis (NMA) which assesses the probability of complete ulcer healing associated with alternative dressings and topical agents.

OBJECTIVES

To assess the effects of dressings and topical agents for healing pressure ulcers in any care setting. We aimed to examine this evidence base as a whole, determining probabilities that each treatment is the best, with full assessment of uncertainty and evidence quality.

SEARCH METHODS

In July 2016 we searched the Cochrane Wounds Specialised Register; the Cochrane Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE; Ovid MEDLINE (In-Process & Other Non-Indexed Citations); Ovid Embase and EBSCO CINAHL Plus. We also searched clinical trials registries for ongoing and unpublished studies, and scanned reference lists of relevant included studies as well as reviews, meta-analyses, guidelines and health technology reports to identify additional studies. There were no restrictions with respect to language, date of publication or study setting.

SELECTION CRITERIA

Published or unpublished randomised controlled trials (RCTs) comparing the effects of at least one of the following interventions with any other intervention in the treatment of pressure ulcers (Stage 2 or above): any dressing, or any topical agent applied directly to an open pressure ulcer and left in situ. We excluded from this review dressings attached to external devices such as negative pressure wound therapies, skin grafts, growth factor treatments, platelet gels and larval therapy.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed study selection, risk of bias assessment and data extraction. We conducted network meta-analysis using frequentist mega-regression methods for the efficacy outcome, probability of complete healing. We modelled the relative effectiveness of any two treatments as a function of each treatment relative to the reference treatment (saline gauze). We assumed that treatment effects were similar within dressings classes (e.g. hydrocolloid, foam). We present estimates of effect with their 95% confidence intervals for individual treatments compared with every other, and we report ranking probabilities for each intervention (probability of being the best, second best, etc treatment). We assessed the certainty (quality) of the body of evidence using GRADE for each network comparison and for the network as whole.

MAIN RESULTS

We included 51 studies (2947 participants) in this review and carried out NMA in a network of linked interventions for the sole outcome of probability of complete healing. The network included 21 different interventions (13 dressings, 6 topical agents and 2 supplementary linking interventions) and was informed by 39 studies in 2127 participants, of whom 783 had completely healed wounds.We judged the network to be sparse: overall, there were relatively few participants, with few events, both for the number of interventions and the number of mixed treatment contrasts; most studies were small or very small. The consequence of this sparseness is high imprecision in the evidence, and this, coupled with the (mainly) high risk of bias in the studies informing the network, means that we judged the vast majority of the evidence to be of low or very low certainty. We have no confidence in the findings regarding the rank order of interventions in this review (very low-certainty evidence), but we report here a summary of results for some comparisons of interventions compared with saline gauze. We present here only the findings from evidence which we did not consider to be very low certainty, but these reported results should still be interpreted in the context of the very low certainty of the network as a whole.It is not clear whether regimens involving protease-modulating dressings increase the probability of pressure ulcer healing compared with saline gauze (risk ratio (RR) 1.65, 95% confidence interval (CI) 0.92 to 2.94) (moderate-certainty evidence: low risk of bias, downgraded for imprecision). This risk ratio of 1.65 corresponds to an absolute difference of 102 more people healed with protease modulating dressings per 1000 people treated than with saline gauze alone (95% CI 13 fewer to 302 more). It is unclear whether the following interventions increase the probability of healing compared with saline gauze (low-certainty evidence): collagenase ointment (RR 2.12, 95% CI 1.06 to 4.22); foam dressings (RR 1.52, 95% CI 1.03 to 2.26); basic wound contact dressings (RR 1.30, 95% CI 0.65 to 2.58) and polyvinylpyrrolidone plus zinc oxide (RR 1.31, 95% CI 0.37 to 4.62); the latter two interventions both had confidence intervals consistent with both a clinically important benefit and a clinically important harm, and the former two interventions each had high risk of bias as well as imprecision.

AUTHORS' CONCLUSIONS

A network meta-analysis (NMA) of data from 39 studies (evaluating 21 dressings and topical agents for pressure ulcers) is sparse and the evidence is of low or very low certainty (due mainly to risk of bias and imprecision). Consequently we are unable to determine which dressings or topical agents are the most likely to heal pressure ulcers, and it is generally unclear whether the treatments examined are more effective than saline gauze.More research is needed to determine whether particular dressings or topical agents improve the probability of healing of pressure ulcers. The NMA is uninformative regarding which interventions might best be included in a large trial, and it may be that research is directed towards prevention, leaving clinicians to decide which treatment to use on the basis of wound symptoms, clinical experience, patient preference and cost.

Topical application of morphine for wound healing and analgesia in patients with oral lichen planus: a randomized, double-blind, placebo-controlled study

OBJECTIVE

The objective of this study was to investigate the effect of topical morphine on erosive/ulcerative lesions in patients with oral lichen planus (OLP). Previous studies reported on an enhanced remission of skin wounds when morphine was applied topically.

MATERIALS AND METHODS

This was single-center, prospective, double-blind, placebo-controlled, randomized, multi-arm (3), phase II study (RCT). Patients diagnosed with erosive and/or ulcerative OLP applied 0.2 or 0.4 mg morphine dissolved in glycerine, three times a day for 5 days. The primary outcome was the extent of healing. Secondary outcomes were as follows: (1) effect on pain, (2) presence and severity of opioid-related central and local side effects, (3) whether patients required 'rescue medication' for treatment of pain, and (4) total intake of test substance.

RESULTS

A total of 123 patients were screened for eligibility, 45 patients were recruited into the study, and 43 completed it. Patients applied a solution of either placebo or 0.2 or 0.4% morphine in groups of n = 12, n = 15, and n = 16, respectively. Extent of healing was similar in the three groups. Severity of pain was minor pre-treatment and throughout the course of the study. Only minor adverse events were reported (dry mouth, burning sensation).

CONCLUSION

Morphine did not enhance wound healing compared to placebo-treated patients. Healing was observed in all groups, which may be attributed to an effect of glycerine or to the natural course of the disease. Patients experienced only mild levels of pain, rendering the model insensitive for assessing pain.

CLINICAL RELEVANCE

OLP is a chronic disease and current treatment options are limited. Healing occurred in all three study groups, an effect we attribute to the carrier.

A randomized, controlled, clinical pilot study assessing the analgesic effect of morphine applied topically onto split-thickness skin wounds

OBJECTIVES

To assess the effect of an opioid administered topically onto a standardized skin wound in patients without significant comorbidity. Findings to date are contradictory, often obtained from multimorbid patients with wounds lacking uniformity.

METHODS

Forty-four patients undergoing surgery for skin grafting were randomly assigned to receive morphine (0.25, 0.75 or 1.25 mg/100 cm(2) wound size) in hydroxyethylcellulose gel or placebo applied onto the excised split-thickness donor wound at the end of surgery. Pain, supplementary systemic opioids and adverse effects were assessed during the first 24 h after application. Healing was examined when the dressings were removed.

KEY FINDINGS

Morphine doses ranged from 0.25 to 5.4 mg (mean 1.93 ± standard deviation 1.34 mg). No differences in pain scores or use of supplementary analgesics were found between the groups. Serious adverse effects did not occur; healing was not impaired. Large intragroup variability was observed for pain scores, wound sizes and supplementary analgesia.

CONCLUSIONS

Patients treated with topically applied morphine gel onto standardized skin wounds did not report lower pain scores compared with placebo-treated patients. Larger groups would be required to arrive at definitive conclusions. The split-thickness skin graft model can be used for future research.

Topical analgesics in the management of acute and chronic pain

Oral analgesics are commonly prescribed for the treatment of acute and chronic pain, but these agents often produce adverse systemic effects, which sometimes are severe. Topical analgesics offer the potential to provide the same analgesic relief provided by oral analgesics but with minimal adverse systemic effects. This article describes the results of a systematic review of the efficacy of topical analgesics in the management of acute and chronic pain conditions. A literature search of MEDLINE/PubMed was conducted using the keywords topical analgesic AND chronic pain OR acute pain OR neuropathic pain and focused only on individual clinical trials published in English-language journals. The search identified 92 articles, of which 65 were eligible for inclusion in the review. The most commonly studied topical analgesics were nonsteroidal anti-inflammatory drugs (n=27), followed by lidocaine (n=9), capsaicin (n=6), amitriptyline (n=5), glyceryl trinitrate (n=3), opioids (n=2), menthol (n=2), pimecrolimus (n=2), and phenytoin (n=2). The most common indications were acute soft tissue injuries (n=18), followed by neuropathic pain (n=17), experimental pain (n=6), osteoarthritis and other chronic joint-related conditions (n=5), skin or leg ulcers (n=5), and chronic knee pain (n=2). Strong evidence was identified for the use of topical diclofenac and topical ibuprofen in the treatment of acute soft tissue injuries or chronic joint-related conditions, such as osteoarthritis. Evidence also supports the use of topical lidocaine in the treatment of postherpetic neuralgia and diabetic neuropathy. Currently, limited evidence is available to support the use of other topical analgesics in acute and chronic pain.

Topical agents or dressings for pain in venous leg ulcers

BACKGROUND

Venous leg ulcers affect up to 1% of people at some time in their lives and are often painful. The main treatments are compression bandages and dressings. Topical treatments to reduce pain during and between dressing changes are sometimes used.

OBJECTIVES

To determine the effects of topical agents or dressings for pain in venous leg ulcers.

SEARCH METHODS

For this third update the following databases were searched: Cochrane Wounds Group Specialised Register (searched 9 May 2012); The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 4); Ovid MEDLINE (2009 to April Week 4 2012); Ovid MEDLINE (In-Process & Other Non-Indexed Citations May 08, 2012); Ovid EMBASE (2009 to 2012 Week 18); and EBSCO CINAHL (2009 to May 2 2012). No date or language restrictions were applied.

SELECTION CRITERIA

Published or unpublished randomised controlled trials (RCTs) that evaluated the effects of topical agents or dressing for the treatment of pain in venous ulcers were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed trial selection, data extraction and risk of bias assessment.

MAIN RESULTS

Six trials (343 participants) evaluated Eutectic Mixture of Local Anaesthetics (EMLA): lidocaine-prilocaine cream for the pain associated with ulcer debridement. The between-group difference in pain measured on a 100 mm scale was statistically significant in favour of EMLA (MD -20.65, 95% CI -12.19 to -29.11). No significant between-group differences in burning or itching were observed.Two trials (470 participants with venous leg ulcers) evaluated ibuprofen slow-release foam dressings for persistent venous leg ulcer pain. Compared with local best practice, significantly more participants in the ibuprofen dressing group achieved the outcome of >50% of the total maximum pain relief score between day 1 and day 5 than participants in the local best practice group (RR 1.63, 95% CI 1.24 to 2.15). The number needed to treat was 6 (95% CI 4 to 12). In the second trial, compared with an identical non-ibuprofen foam dressing, there was no statistically significant difference in the proportion of participants experiencing slight to complete pain relief on the first evening of treatment.Limited data were available to assess healing rates or adverse events.

AUTHORS' CONCLUSIONS

There is some evidence to suggest that ibuprofen dressings may offer pain relief to people with painful venous leg ulcers. EMLA (5%) appears to provide effective pain relief during the debridement of venous leg ulcers. Further research should consider standardised pain assessment methods and assess both the effect on ulcer healing and the impact of long term use of these treatments.

Topical morphine gel in the treatment of painful leg ulcers, a double-blind, placebo-controlled clinical trial: a pilot study

Chronic painful wounds, a major health problem, have a detrimental impact on the quality of life due to associated pain. Some clinical reports have suggested that local administration of morphine could be beneficial. The aim of this study was to evaluate the analgesic effect of topically applied morphine on chronic painful leg ulcers. Twenty-one patients were randomly assigned to receive either morphine or placebo in a randomised, placebo-controlled, crossover pilot study. Each patient was treated four times in total. Pain was measured by the visual analogue score (VAS) before application of gel, directly after and after 2, 6, 12 and 24 hours. Although an overall, clinically relevant, reduction of pain was observed upon treatment with morphine, the difference was not statistically significant. Morphine reduced pain scores more than placebo on treatment occasions 1 and 2. The difference was statistically significant only 2 hours after dressing on the first treatment occasion. Thus, our study did not demonstrate a consistent and globally significant difference in nociception in patients treated with morphine. However, the relatively small number of patients included in our study and other methodological limitations makes it difficult for us to draw general conclusions regarding efficacy of topically applied morphine as an effective treatment for some painful ulcers. Further studies are warranted to evaluate the value of topically applied morphine in the treatment of patients with chronic painful leg ulcers.

Should topical opioid analgesics be regarded as effective and safe when applied to chronic cutaneous lesions?

Objectives

The induction of analgesia for many chronic cutaneous lesions requires treatment with an opioid analgesic. In many patients suffering with these wounds such drugs are either contraindicated or shunned because of their association with death. There are now case reports involving over 100 patients with many different types of chronic superficial wounds, which suggest that the topical application of an opioid in a suitable gel leads to a significant reduction in the level of perceived pain.

Key findings

Some work has been undertaken to elucidate the mechanisms by which such a reduction is achieved. To date there have been no proven deleterious effects of such an analgesic system upon wound healing. Although morphine is not absorbed through the intact epidermis, an open wound provides no such barrier and for large wounds drug absorption can be problematic. However, for most chronic cutaneous lesions, where data has been gathered, the blood levels of the drug applied ranges from undetectable to below that required for a systemic effect.

Summary

If proven, the use of opioids in this way would provide adequate analgesia for a collection of wounds, which are difficult to treat in patients who are often vulnerable. Proof of this concept is now urgently required.

The management of cancer pain

The experience of pain in cancer is widely accepted as a major threat to quality of life, and the relief of pain has emerged as a priority in oncology care. Pain is associated with both the disease as well as treatment, and management is essential from the onset of early disease through long-term survivorship or end-of-life care. Effective relief of pain is contingent upon a comprehensive assessment to identify physical, psychological, social, and spiritual aspects and as a foundation for multidisciplinary interventions. Fortunately, advances in pain treatment and in the field of palliative care have provided effective treatments encompassing pharmacological, cognitive-behavioral, and other approaches. The field of palliative care has emphasized that attention to symptoms such as pain is integral to quality cancer care.

Care of chronic wounds in palliative care and end-of-life patients

The aim of this paper was to provide a literature synthesis on current wound care practices for the management of chronic wounds in palliative care and end-of-life patients, focusing on the control of wound-related symptoms for comfort and improved quality of life. These wounds included pressure ulcers, venous and arterial leg ulcers, diabetic ulcers and fungating malignant wounds. Wound-related symptoms included pain, exudate, malodour, infection, bleeding, dressing comfort and negative psychological and social functioning. Best care wound practices were formulated for each wound type to ease suffering based on the literature review. Although symptom management strategies for comfort may work in tandem with healing interventions, it is important to recognise when efforts towards wound closure may become unrealistic or burdensome for the patient at end of life. Thus, unique aspects of palliative wound care feature clinical indicators for early recognition of delayed healing, quality of life measurement tools related to chronic wounds, and comfort care strategies that align with patient wishes and realistic expectations for wound improvement.

Topical agents or dressings for pain in venous leg ulcers

BACKGROUND

Venous leg ulcers affect up to 1 per cent of people at some time in their lives. The main treatments are compression bandages and dressings. As these ulcers are often painful some clinicians choose particular dressings and topical treatments (analgesia/ local anaesthetic) to reduce the pain both during and between dressing changes.

OBJECTIVES

To assess the effectiveness of dressings, local anaesthetics or topical analgesia for pain relief in venous leg ulceration.

SEARCH STRATEGY

For this update the search strings were revised and the following databases were searched: The Cochrane Wounds Group Specialised Register (Searched 16/12/09) The Cochrane Central Register of Controlled Trials (CENTRAL) - The Cochrane Library Issue 4 2009; Ovid MEDLINE - 1950 to November Week 3 2009; Ovid EMBASE - 1980 to 2009 Week 50; EBSCO CINAHL - 1982 to December 16 2009. No date or language restrictions were applied.

SELECTION CRITERIA

Randomised controlled trials which evaluated local interventions used to relieve venous leg ulcer pain were considered. Pain was defined as either persistent pain or pain at dressing changes or debridement. Ulcer healing and reported adverse events were also considered as further outcomes.

DATA COLLECTION AND ANALYSIS

Eligibility for inclusion was confirmed by two review authors who independently assessed the potential trials.

MAIN RESULTS

Two trials evaluating interventions for persistent venous leg ulcer pain were identified for this review update. Both studies evaluated ibuprofen slow release foam dressings; one comparing it with local best practice and the other with an identical foam comparator. The primary end point for both studies was "pain relief achieved". When compared with a foam dressing alone, there was no evidence of a statistically significant effect of the ibuprofen foam dressing in terms of achieving some pain relief the first evening after treatment: 74% in the ibuprofen group (46/62) had pain relief compared with 58% (35/60) in the foam group (no significant difference: RR 1.27, 95%CI 0.98 to 1.65). In the second study 100% (32/32) of people with venous ulcers achieved some pain relief with the ibuprofen dressing on the first evening of treatment compared with 93% (26/28) in the local best practice group (no significant difference: RR 1.08, 95% CI 0.96 to 1.21). Pooling these studies in a meta-analysis (using a random effects model as significant heterogeneity present (p=0.1), I(2) = 64%) there is no evidence that ibuprofen dressings increase the pain relief experienced by the first evening of use (RR 1.15, 95% CI 0.91 to 1.44). We were not able to extract sufficient data to combine other pain outcomes from these trials. There was no difference in healing rates but slightly more adverse events with ibuprofen dressings than with a similar foam dressing without ibuprofen.Six trials evaluated interventions for the pain associated with debridement and were considered sufficiently similar to pool. There was a statistically significant reduction in debridement pain scores with 5% Eutectic Mixture of Local Anaesthetics (EMLA): lidocaine-prilocaine cream; the difference in means (measured on a 100 mm scale) was 20.6 mm (95% CI 12.19 to 29.11). Of these six trials, only one small trial measured healing as an outcome and found no difference in the numbers of ulcers healed at the end of the study.

AUTHORS' CONCLUSIONS

There is no evidence that ibuprofen dressings offer pain relief, as measured at the first evening of use, to people with painful venous leg ulcers compared with foam dressings or best practice.EMLA appears to provide effective pain relief for venous leg ulcer debridement but the effect (if any) of EMLA on ulcer healing remains unknown.

Effectiveness of topical administration of opioids in palliative care: a systematic review

The discovery of peripheral opioid receptors has become the scientific basis for topical use of opioids in malignant and nonmalignant ulcers and oropharyngeal mucositis. This systematic review aimed to assess the quality of published literature and to examine whether topical opioids are effective in controlling pain in palliative care settings. After a systematic literature review, 19 studies (six randomized controlled trials [RCTs] and 13 case reports) met the inclusion criteria for the review. Eighteen studies favored topical opioids in pain relief, as evidenced by reductions in post-treatment pain scores, but time to onset and duration of analgesia varied widely. Because of the heterogeneity of the studies, meta-analysis was not possible. Despite clear clinical benefits described in small RCTs, there is a deficiency of higher-quality evidence on the role of topical opioids, and more robust primary studies are required to inform practice recommendations. N-of-1 trials should be encouraged for specific clinical circumstances.

Topical dressings to manage pain in venous leg ulceration

The pain experienced by patients with venous leg ulceration can be severe, disabling and have an impact on their quality of life. Pain assessment should be an integral part of leg ulcer assessment, since unless pain is successfully managed, the patient may not be able to comply with compression bandaging or exercise and elevation, all of which are crucial components in the successful management of venous leg ulceration. Neuropathic pain can be difficult to identify for both patient and healthcare professional, if it is unrecognized and untreated the patient's ulceration may persist due to an inability to tolerate dressings or bandaging.

Incorporating wound healing strategies to improve palliation (symptom management) in patients with chronic wounds

BACKGROUND

Palliative wound care should be centered on symptom management and is a viable option for patients whose chronic wounds do not respond to standard interventions, or when the demands of treatment are beyond the patient's tolerance or stamina. Palliative wound care is the incorporation of strategies that prioritize symptomatic relief and wound improvement ahead of wound healing (total closure). Palliative wound care strategies must also work in conjunction with curative treatment objectives as wounds often heal completely in spite of serious illness and advanced disease. Palliative wound care is much more than pain, exudate and odor management. Common curative treatment goals such as physical correction of the underlying pathology, addressing nutrition and other supportive aspects of care, and sensible (nonharmful) local wound treatments should never be ignored.

OBJECTIVE

(1) To provide a fresh and effective approach to palliative wound care by integrating individual clinical expertise with clinical and laboratory evidence from the (curative) wound healing literature and (2) to share our (Calvary Hospital) experience and approach to palliative wound care in an inpatient, home, and outpatient setting. This approach can be summarized with the mnemonic S-P-E-C-I-A-L (S = stabilizing the wound, P = preventing new wounds, E = eliminate odor, C = control pain, I = infection prophylaxis, A = advanced, absorbent wound dressings, L = lessen dressing changes). Throughout this paper we will offer rationale, principles and recipes, for each of the steps of the "SPECIAL" approach in an effort to facilitate the caring for chronic wounds in palliative medicine.

CONCLUSIONS

A practical marriage of wound palliation (symptom management) with current wound healing concepts to provide options for the palliative care provider and improve the practice of palliative medicine.

A randomised controlled trial to test the analgesic efficacy of topical morphine on minor superficial and partial thickness burns in accident and emergency departments

OBJECTIVES

To test the analgesic efficacy of topical morphine on superficial burns within the emergency department by comparing pain scores, comfort ratings and analgesia taken by participants.

METHOD

A placebo-controlled three-treatment randomised controlled trial was undertaken. 59 participants were randomly allocated to receive a dressing containing Intrasite gel and morphine sulphate, Intrasite gel and water or the conventional Jelonet dressing. The study design enabled double-blinding between the two Intrasite gel treatments.

RESULTS

49 participants were included in the final analysis as 10 were lost to follow-up. No significant differences were observed between the pain scores or comfort ratings of the three treatments. Participants receiving Jelonet and the placebo reduced their pain scores by the greatest amount overall. However, participants receiving morphine were the only group to reduce pain scores by >20 mm on two consecutive time intervals (2 and 6 h). At 12 h the morphine group reported the highest pain scores. Only 4/15 participants receiving topical morphine administered additional analgesia compared with 12/17 receiving the Jelonet dressing and 6/17 receiving Intrasite and water (p = 0.055). However, when all analgesia was taken into account, the morphine group was administered the greatest amount. Overall, the placebo group reported their dressings to be the most comfortable and took the least amount of analgesia. Minor adverse reactions included itching, burning and a rash. No serious adverse reactions were reported.

CONCLUSIONS

Topical morphine sulphate does not seem to be as effective when used for the pain associated with superficial burns as when used for the pain associated with chronic inflammatory wounds. (The European Clinical Trials Database number for this study is 2005-003285-42.).

Topical agents for the treatment of chronic pain

Unlike systemic analgesics, topical analgesics exert their analgesic activity locally and without significant systemic absorption. This is in contrast to transdermal analgesics, which require systemic absorption for clinical benefit. The mechanism of action of a particular topical analgesic is unique to the specific medication being used as a topical analgesic. Topical analgesics have been studied in an increasing number of painful clinical conditions, and the results of some of these studies are summarized in this article. The potential role of topical analgesics acting peripherally in affecting the central processing of pain as well as painful states considered to be "central," not "peripheral," also are reviewed.