The effectiveness of topically applied capsaicin. A meta-analysis

Systematic review of topical capsaicin for the treatment of chronic pain

OBJECTIVE

To determine the efficacy and safety of topically applied capsaicin for chronic pain from neuropathic or musculoskeletal disorders.

DATA SOURCES

Cochrane Library, Medline, Embase, PubMed, an in-house database, and contact with manufacturers of topical capsaicin.

STUDY SELECTION

Randomised controlled trials comparing topically applied capsaicin with placebo or another treatment in adults with chronic pain.

DATA EXTRACTION

Primary outcome was dichotomous information for the number of patients with about a 50% reduction in pain. Outcomes were extracted at four weeks for musculoskeletal conditions and eight weeks for neuropathic conditions. Secondary outcomes were adverse events and withdrawals due to adverse events.

DATA SYNTHESIS

Six double blind placebo controlled trials (656 patients) were pooled for analysis of neuropathic conditions. The relative benefit from topical capsaicin 0.075% compared with placebo was 1.4 (95% confidence interval 1.2 to 1.7) and the number needed to treat was 5.7 (4.0 to 10.0). Three double blind placebo controlled trials (368 patients) were pooled for analysis of musculoskeletal conditions. The relative benefit from topical capsaicin 0.025% or plaster compared with placebo was 1.5 (1.1 to 2.0) and the number needed to treat was 8.1 (4.6 to 34). Around one third of patients experienced local adverse events with capsaicin, which would not have been the case with placebo.

CONCLUSIONS

Although topically applied capsaicin has moderate to poor efficacy in the treatment of chronic musculoskeletal or neuropathic pain, it may be useful as an adjunct or sole therapy for a small number of patients who are unresponsive to, or intolerant of, other treatments.

Pharmacological treatments for persistent non-malignant pain in older persons

Persistent non-malignant pain is common, often neglected and under-treated among older persons. Some older adults do not complain because they consider chronic pain to be a characteristic of normal aging. Physicians have concerns regarding adverse effects of pharmacological treatment. The model of the World Health Organization for treatment of cancer pain is generally accepted and also recommended for persistent non-cancer pain. Furthermore, non-pharmacological treatment should complement drug treatment whenever possible. An initial assessment and possible treatment of underlying causes of pain are pertinent. Modern pharmacological pain management is based on non-opioid and opioid analgesics. NSAIDs are among the most widely prescribed class of drugs in the world. The new cyclo-oxygenase-2 inhibitors such as celecoxib and rofecoxib offer an alternative for the treatment of mild-to-moderate pain in patients with a history of gastric ulcers or bleeding. Paracetamol (acetaminophen) is being used widely for the management of mild pain across all age groups as it has moderate adverse effects at therapeutic dosages. For moderate pain, a combination of non-opioid analgesics and opioid analgesics with moderate pain relief properties (e.g. oxycodone, codeine, tramadol and tilidine/naloxone) is recommended. For severe pain, a combination of non-opioid analgesics and opioid analgesics with strong pain relief properties (e.g. morphine, codeine) is recommended. The least toxic means of achieving systemic pain relief should be used. For continuous pain, sustained-release analgesic preparations are recommended. Drugs should be given on a fixed time schedule, and possible adverse effects and interactions should be carefully monitored. Adjuvant drugs, such as antidepressants or anticonvulsants, can be very effective especially in the treatment of certain types of pain, such as in diabetic neuropathy. Effective pain management should result in decreased pain, increased function and improvement in mood and sleep.

Selected CAM Therapies for Arthritis-Related Pain: The Evidence From Systematic Reviews

OBJECTIVES

The purpose is to examine what is known about the efficacy of selected complementary and alternative medicine (CAM) therapies for pain from arthritis and related conditions based on systematic reviews and meta-analyses.

METHODS

Results specifically related to pain were retrieved from review articles of acupuncture, homeopathy, herbal remedies, and selected nutritional supplements.

RESULTS

Evidence exists to support the efficacy of reducing pain from osteoarthritis (OA) for acupuncture; devil's claw, avocado/soybean unsaponifiables, Phytodolor and capsaicin; and chondroitin, glucosamine, and SAMe. Strong support exists for gamma linolenic acid (GLA) for pain of rheumatoid arthritis (RA).

CONCLUSIONS

Despite support for some of the most popular CAM therapies for pain from arthritis-related conditions, additional high quality research is needed for other therapies, especially for herbals and homeopathy.

New treatments for diabetic neuropathy: symptomatic treatments

Painful diabetic neuropathy is a common distressing and challenging condition. The mechanism or mechanisms involved in its pathogenesis continue to elude clinical scientists. As with other conditions of painful distal symmetrical neuropathic conditions, pain relief involves the use of a variety of analgesic and neuroleptic drugs, aimed at reducing either central responses to painful stimuli or at dampening spontaneous irritability of affected neurons. More recently, several therapies directed at putative pathologic mechanisms specific to painful diabetic neuropathy have evolved. These include vasodilators, protein kinase C beta inhibition, antioxidants, and novel aldose reductase inhibitors. Preliminary clinical studies of these therapies have at present involved small numbers of patients; however, the results have been encouraging. This article considers the clinical aspects of diagnosis and management of chronic painful diabetic neuropathy, focusing on existing and newer therapies.

Medical evaluation and treatment of diabetic peripheral neuropathy

Diabetes mellitus is a major health concern that is only expected to become more prevalent over the next few decades. It causes much morbidity and mortality through various macro- and microvascular complications, including diabetic neuropathy. Currently, there is no treatment that directly affects the natural course of diabetic neuropathy except for rigorous glycemic control, a goal that is not always achievable. Despite these therapeutic limitations, the morbidity caused by diabetic neuropathy can be minimized by early and accurate diagnosis. A detailed history and physical examination, along with carefully selected laboratory tests will confirm the presence of diabetic neuropathy while excluding other etiologies that may require alternative management strategies. Treatment is always tailored to the patient's symptoms. In addition to improved glycemic control, health care providers can provide education, support, and symptomatic relief. There are many pain modulating therapies that are effective in diabetic neuropathy as discussed above. Nortriptyline at low doses is an inexpensive well-tolerated medication that is effective. Gabapentin is an excellent choice when nortriptyline is ineffective or not tolerated. Other anticonvulsants, such as lamotrigine, carbamazepine, oxycarbazepine, and topiramate, may also provide benefit. Judicious use of narcotics is appropriate when other treatment modalities fail. The importance of treating underlying depression cannot be overemphasized. When gait becomes impaired as a result of neuropathy, appropriate prescription of assistive devices will prevent injuries from falls. Ankle-foot orthoses and other orthotic devices may allow patients to remain ambulatory and independent for a longer period. Despite the challenges ahead, the future holds the promise of more effective treatments for diabetes mellitus and its complications.

'Natural remedies' in the treatment of osteoarthritis

Osteoarthritis (OA) is a common, chronic and painful condition. It is the most common of all rheumatic disorders and is destined to become one of the most prevalent and costly diseases in our society. The conventional therapeutic options employed in the management of OA are simple analgesics and NSAIDs, but these options frequently produce sub-optimal benefit and are associated with an adverse-safety profile. Unsurprisingly patients are looking to alternative and complementary medicine. The aim of this article was to review the available literature on the effectiveness and safety of 'natural remedies' for the treatment of OA. Computerised literature searches were carried out for systematic reviews and randomised controlled trials examining the role of 'natural remedies' in the treatment of OA. There have been few randomised controlled trials of 'natural remedies' that have satisfied the internationally agreed standards. There was, however, evidence of efficacy for glucosamine, chondroitin sulfate and possibly avocado/soybean unsaponifiables for the symptomatic relief of OA. To date, it is not established whether any of the 'natural remedies' are capable of chondroprotection. Even if 'natural remedies' are only modestly effective, they are widely available and well tolerated, suggesting that they may play a significant role in the management of OA in the elderly.

Management strategies for the treatment of neuropathic pain in the elderly

Pain caused by dysfunction or damage to the peripheral or central nervous system is typified by the symptoms described by patients with painful diabetic neuropathy, post-herpetic neuralgia and central poststroke pain. All these conditions are more common in the elderly. Neuropathic pain has long been recognised as one of the more difficult types of pain to treat; however, with the current emphasis on providing a multidisciplinary assessment and approach to management, more patients will be offered relief of their symptoms and an improved quality of life. Despite the use of combination drug therapy, adequate pain relief in the elderly is difficult to achieve without adverse effects. In an attempt to minimise these it is important to include non-drug treatment options in the management plan. Lifestyle changes and environmental modification, together with encouragement to adopt an appropriate exercise programme and an emphasis on maintaining mobility and independence should always be considered. Interventional therapy ranging from simple nerve blocks to intrathecal drug delivery can be of value. Drug treatment remains the mainstay of therapy. Tricyclic antidepressants such as amitriptyline, while having significant adverse effects in the elderly, have a number needed to treat (NNT) of 3.5 for 50% pain relief in diabetic neuropathy and 2.1 for 50% pain relief in postherpetic neuralgia. The newer antiepileptic drugs, such as gabapentin, appear to have a better adverse effect profile and provide similar efficacy with the NNT for treating painful diabetic neuropathy being 3.7 and 3.2 for treating pain in postherpetic neuralgia. As our understanding of the complexities of the pain processes increases, we are becoming more able to appropriately combine treatments to achieve not only improved pain relief but also improved function.

Treatment of symptomatic diabetic neuropathy

Painful diabetic neuropathy is a common and particularly unpleasant long-term complication of diabetes that affects a significant minority of patients with distal polyneuropathy. After exclusion of other causes of neuropathic pain, attention should be focused on achieving optimal and stable glycaemic control avoiding flux of blood glucose levels, which have been shown to aggravate pain. Most patients will require pain control therapy and whilst the tricyclic drugs remain a first-line approach, their use is often hampered by predictable but troublesome side effects. Gabapentin, the only agent specifically licensed for the treatment of neuropathic pain in the United Kingdom, is useful in diabetic neuropathy and is generally better tolerated than the tricyclics. Additionally, other pharmacological and non-pharmacological pain management approaches may be useful. Patient education has a significant role to play in the avoidance of late neurological complications.

Managing chronic arthritis

Many compounds are being investigated for the control of symptoms of osteoarthritis in people and animals. Ideally, treatment should include analgesia, inflammation control, and chondroprotection. With further progress in this area, combination therapies tailored to the needs of the individual animal should enable us to maximize efficacy and minimize side effects. Only a few of the newer therapies and pharmaceutic agents have been investigated in the horse, however. With more rigorous investigation, they may be determined to be ineffective or unsafe. Meanwhile, as much information should be gathered from manufacturers as possible so as to ensure that appropriate recommendations are made.

Determination of capsaicinoids in topical cream by liquid-liquid extraction and liquid chromatography

A reversed-phase liquid chromatography (LC) method has been developed, optimised and validated for the separation and quantitation of capsaicin (CP) and dihydrocapsaicin (DHCP) in a topical cream formulation. Sample preparation involves liquid-liquid extraction prior to LC analysis. The method uses a Hypersil C(18) BDS, 5 micrometer, 250x4.6 mm I.D. column maintained at 35 degrees C. The mobile phase comprises methanol, water, acetonitrile (ACN) and acetic acid (47:42:10:1, v/v/v/v) at a flow rate of 1.0 ml/min. Robustness was evaluated by performing a central composite face-centred design (CCF) experiment. The method shows good selectivity, linearity, sensitivity and repeatability. The conditions allow the separation and quantitation of CP and DHCP without interference from the other substances contained in the cream.

Update on diabetic neuropathy

PURPOSE OF REVIEW

This review will focus on recent advances in the field of diabetic neuropathy, with an emphasis on distal symmetric sensory and sensorimotor polyneuropathy. Some new information in the areas of diabetic amyotrophy and diabetic autonomic neuropathy will also be reviewed.

RECENT FINDINGS

The pathogenesis of diabetic neuropathy is multifactorial. There is increasing evidence to link abnormalities in the polyol pathway to the pathogenesis of diabetic neuropathy. In addition, there appear to be abnormalities of nerve regeneration and of sodium and calcium channels. Aldose reductase inhibitors have shown promise in animal models for reversing neuropathy if started early and used for a sufficient time, but those used to date in human trials are probably not of sufficient potency. Neurotrophic factors and vascular endothelial growth factor both also show promise. Specific recommendations and pathways for diabetic foot care have been devised. Lamotrigine and bupropion represent new treatments for neuropathic pain. The role of impaired glucose tolerance is being explored as it relates to polyneuropathy.

SUMMARY

An increasing understanding of the pathogenetic mechanisms holds out promise for the effective treatment of diabetic neuropathy. The early detection of abnormal glucose metabolism is particularly important, as treatments will probably be most effective if administered early in the course of the neuropathy, when abnormalities of peripheral nerves are more likely to be reversible.

In vitro topical application and in vivo pharmacodynamic evaluation of nonivamide hydrogels using Wistar rat as an animal model

Nonivamide, a so-called synthetic capsaicin, is a substitute for capsaicin which has a similar chemical structure and pharmacological activities as those of capsaicin. The purposes of this study were to explore the in vivo pharmacodynamic responses of nonivamide in hydrogels using Wistar rat as an animal model and to correlate the in vivo results with in vitro topical application. The incorporation of Pluronic F-127 polymer into hydrogels resulted in retarded release of nonivamide. Chitosan and carboxymethylcellulose hydrogels produced higher levels of in vitro nonivamide permeation and skin distribution. The in vivo effects of nonivamide on skin perturbation and vasodilation were found to differ depending on dose and duration after topical application. Quantification of transepidermal water loss was demonstrated to correlate with the measured in vitro skin distribution of nonivamide. The various doses of nonivamide in the hydrogels did not markedly influence erythematous reactions of skin as determined by colorimetric measurements. Hydrogel formulations of nonivamide delivered more drug to the skin and produced greater pharmacodynamic activities than did cream bases of capsaicin.

Skin infections and infestations in geriatric patients

Geriatric patients develop infections, but many have a different appearance from what usually is expected. The difference depends on the age and immune status of the patient and the virulence of the organism. Differences may make recognition more difficult. Therapy may require different doses. Examples of the more common infections are detailed in this article.

Meeting the therapeutic challenge of the patient with osteoarthritis

OBJECTIVE

To discuss the diagnosis of osteoarthritis and the efficacy of available pharmacologic and nonpharmacologic treatment options.

DATA SOURCES

Published reports on the diagnosis and treatment of osteoarthritis were identified through a MEDLINE search of English-language journal articles using a focused title search for the keywords acetaminophen, nonsteroidal anti-inflammatory, COX-2 nonsteroidal, opioids, capsaicin, tramadol, glucosamine, hyaluronic acid, and osteoarthritis and by reviewing the bibliographies of selected reviews. The American College of Rheumatology (ACR) guidelines, as updated in September 2000, for the treatment of osteoarthritis of the hip and knee were analyzed with appropriate references to clinical and scientific studies, review articles, and other published guidelines.

DATA SYNTHESIS

Each patient's medical history and level of pain should decide the most appropriate treatment. Nonpharmacologic therapies should always be included in the treatment regimen. If further pain management is required, the most appropriate pharmacologic treatments are acetaminophen or nonsteroidal anti-inflammatory drugs for mild-to-moderate pain, tramadol or opioid combinations for moderate-to-moderately severe pain, and opioids for severe pain. Adjunctive treatments, intraarticular injections, and surgery are also viable options for some patients.

CONCLUSION

If used properly, the ACR guidelines for the treatment of osteoarthritis are important tools in the care of the patient with this disease.

Treatments for diabetic neuropathy

The management of symptomatic diabetic sensory neuropathy presents a therapeutic challenge to the practicing physician. Two approaches are outlined in this article. First, symptomatic therapies, which will not influence the natural history of painful neuropathy, are discussed. These include, in addition to the stable glycemic control, tricyclic drugs, a number of anticonvulsant and antiarrhythmic agents, and opioid-like medications. Topical therapies and nonpharmalogic approaches are also discussed. With the exception of near normoglycemia, treatments that may slow the progression of neuropathy are experimental and include aldose reductase inhibitors, antioxidants, and other agents. Finally, the approach to patients without symptoms but with sensory loss is discussed.

Herbal medicines for the treatment of osteoarthritis: a systematic review

OBJECTIVE

Limitations in the conventional medical management of osteoarthritis indicate a real need for safe and effective treatment of osteoarthritis patients. Herbal medicines may provide a solution to this problem. The aim of this article was to review systematically all randomized controlled trials on the effectiveness of herbal medicines in the treatment of osteoarthritis.

METHODS

Computerized literature searches were carried out on five electronic databases. Trial data were extracted in a standardized, predefined manner and assessed independently.

RESULTS

Twelve trials and two systematic reviews fulfilled the inclusion criteria. The authors found promising evidence for the effective use of some herbal preparations in the treatment of osteoarthritis. In addition, evidence suggesting that some herbal preparations reduce consumption of non-steroidal anti-inflammatory drugs was found. The reviewed herbal medicines appear relatively safe.

CONCLUSIONS

Some herbal medicines may offer a much-needed alternative for patients with osteoarthritis.

Assessment and management of chronic pain in elderly people

The ageing process can bring with it an increased incidence of conditions which give rise to chronic pain. Persistent musculoskeletal and/or neuropathic pain due to conditions such as back pain, arthritis, osteoporosis and diabetes in elderly people can lead to a marked deterioration in their quality of life. Pain assessment can be complicated by concomitant disorientation, confusion and communication deficits, leading to the undertreatment of pain in this client group. Pain management can be difficult due to the existence of multiple medical problems and the increased incidence of side-effects related to the treatment. This article aims to update nurses on the assessment and management of pain in the older adult, and will provide a broad overview of pain management strategies suitable for elderly patients.

Treatment options in painful diabetic neuropathy

Diabetic neuropathy is common in patients with diabetes mellitus, and 7.5% of diabetics experience pain from diabetic neuropathy. Complications of diabetes mellitus are more common where control of the disease is not optimal. By improving the control of the disease, both the neuropathy and the pain it can produce may be improved. The pain of diabetic neuropathy can frequently be controlled using analgesics, antidepressants, anticonvulsants, topical capsaicin, and neuromodulation, either alone or in any combination.

What is the quality of the implemented meta-analytic procedures in chronic pain treatment meta-analyses?

OBJECTIVE

Meta-analysis (MA) is the application of quantitative techniques for the purposes of summarizing data from individual studies. This type of review has many advantages over traditional reviews. However, different investigators performing MAs on the same data set have reached different conclusions. These reliability problems have been attributed to differences in the quality of the implemented meta-analytic procedures. We, therefore, examined the chronic pain treatment meta-analytic literature for MA procedure quality and for the consistency of conclusions. DESIGN, SETTING, PARTICIPANTS, OUTCOME MEASURES: Chronic pain treatment MAs were isolated according to inclusion/exclusion criteria. Data from these MAs were abstracted into structured tables. Table format reflected eight meta-analytic procedures identified previously as being important to MA implementation quality. These were: adequacy of retrieval, publication bias, inclusion/exclusion criteria, abstraction of data, quality, homogeneity/heterogeneity, independence, and statistical versus clinical interpretation. Each meta-analytic procedure was then independently rated by two raters. Rating results were then analyzed by procedure for each individual MA for percentage scores out of 100%, and mean scores. For MAs addressing the same topic area (pain facility treatment, antidepressant treatment, manipulation treatment) direction of effect size was noted. Mean effect sizes were calculated for these subgroups.

RESULTS

Sixteen chronic pain treatment MAs fulfilled inclusion/exclusion criteria. Mean procedure ratings indicated that four procedures may not be implemented adequately. These were publication bias, abstraction of data, quality, and homogeneity/heterogeneity. There was wide MA implementation score variability, with 37.5% scoring less than 50%. The effect sizes of the MA subgroups demonstrated replicate nonvariability.

CONCLUSIONS

Some meta-analytic procedures could be interpreted to be implemented inadequately in some chronic pain treatment MAs. There is wide variability between individual chronic pain treatment MAs on adequacy of implementation of these procedures. However, the effect sizes of the different MA subgroups demonstrated consistency. This finding indicates that for these MA subgroups, MA results are consistent between authors. In addition, chronic pain MAs, as compared with other groups of MAs, appear to address some of the procedures in a more adequate fashion. Future chronic pain MAs should concentrate on improving the quality of their methods with particular emphasis on the above four procedures. Because of potential validity problems with these results, these data cannot and should not be used to make administrative decisions about previous MAs.

Tachykinin receptor modulators: novel therapeutics for rheumatoid arthritis

The activation of a cellular immune response in a genetically susceptible individual is widely recognised as a main step in triggering rheumatoid arthritis (RA). The tachykinins, substance P (SP) and neurokinin A (NKA), can play a major role in different immune diseases. In patients with inflammatory joint disease, elevated levels of SP have been demonstrated in the synovial fluid of affected joints. It is well known that SP and, to a lesser extent, NKA are deeply involved in the processing of nociceptive signals and exert many pro-inflammatory actions, which may be elicited by an increased neuronal neurokinin release in arthritis; the mechanism behind this increase remains to be fully elucidated. Different observations suggest that one approach to the treatment of RA might be to inhibit the local effects of neurokinins in the affected joints. This review will summarise the more relevant aspects of this topic.

Topical agents in the treatment of rheumatic disorders

Topical drug delivery may be the optimal route for the treatment of localized musculoskeletal disorders because higher drug concentrations can be achieved at the sites of clinical significance. The rationale for the use of topical salicylates and other nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of soft-tissue rheumatic complaints and osteoarthritis is reviewed. Topical capsaicin offers another potentially beneficial therapy for the treatment of osteoarthritis of selected joints. Although there are extensive, uncontrolled experiences with DMSO that suggests its effectiveness in the treatment of musculoskeletal disorders, controlled trials yield conflicting results. The basis for the use of physical modalities such as phonophoresis and iontophoresis to improve topical drug efficacy is summarized.

Epidural resiniferatoxin induced prolonged regional analgesia to pain

Adequate treatment of cancer pain remains a significant clinical problem. To reduce side effects of treatment, intrathecal and epidural routes of administration have been used where appropriate to reduce the total dose of agent administered while achieving regional control. Resiniferatoxin (RTX), an ultrapotent capsaicin analog, gives long-term desensitization of nociception via C-fiber sensory neurons. We evaluate here the analgesic effect on rats of epidurally administered RTX, using latency of response to a thermal stimulus in unrestrained animals. Results were compared with those for systemically administered RTX. Vehicle or graded doses of RTX were injected subcutaneously (s.c.) or through an indwelling lumbar (L4) epidural catheter as a single dose. Both routes of application of RTX produced profound thermal analgesia, reaching a plateau within 4-6 h and showing no restoration of pain sensitivity over 7 days. Vehicle was without effect. For the epidural route, the effect was selective as expected for the targeted spinal cord region, whereas the subcutaneous administration of RTX had a generalized analgesic effect. At doses yielding a tripling of back paw withdrawal latency, epidural treatment was 25-fold more effective than the subcutaneous route of application. Consistent with the regional selectivity of the lumbar epidural route, the front paws showed no more effect than by systemic RTX treatment. Binding experiments with [3H]RTX provided further evidence of the segmental desensitization induced by epidural RTX. We conclude that epidural administration of RTX at the lumbar spinal level produces profound, long-lasting, segmental analgesia to C-fiber mediated pain in the rat.

Painful diabetic neuropathy

Chronic painful diabetic neuropathy causes symptoms that can last for many years and severely impair the quality of life of affected patients. This review describes the epidemiology, pathophysiology and treatment of chronic neuropathic pain. Particular emphasis is placed on a comprehensive review of the management of painful symptoms through a detailed review of the published literature using a variety of databases particularly Medline and EMBASE.

Painful diabetic neuropathy

Chronic painful diabetic neuropathy can cause a variety of challenges, particularly in successful treatment. The pain, which can last for years, can severely impair quality of life. Management is difficult, although the careful use of drugs can be significantly beneficial. Tricyclic and anticonvulsant drugs may be effective, with a variety of drugs available as second line agents. Newer non-drug systems such as electrical spinal cord stimulation represent exciting possibilities for the future management of this most difficult diabetic syndrome.

Hyperosmolar saline induces reflex nasal secretions, evincing neural hyperresponsiveness in allergic rhinitis

We investigated whether hyperosmolar saline (HS), applied via paper disk onto the septum of one nostril, induces a nasal secretory response. Furthermore, we examined whether this response is accentuated in patients with active allergic rhinitis (AR) compared with healthy volunteers. Unilateral HS produced significant nasal secretions both ipsilateral and contralateral to the site of challenge in the AR group and only ipsilaterally in the healthy group. The HS-induced nasal secretions were significantly greater in the AR vs. the healthy subjects. In a separate study, we ascertained that the nasal response to HS is neurally mediated and found that ipsilateral nerve blockade with lidocaine significantly attenuates the HS-induced secretions bilaterally. In another group of AR subjects, we determined whether nociceptive fibers were involved in this response and found that sensory nerve desensitization with repeated application of capsaicin attenuated the HS-induced nasal secretions. Finally, we determined whether the secretory hyperresponsiveness in AR is attributable to increased reactivity of submucosal glands rather than of nerves. We found that the dose response to methacholine, which directly stimulates the glands, was identical among AR and healthy subjects. We conclude that, in AR, nasal challenge with HS induces significantly greater reflex secretions involving capsaicin-sensitive nerve fibers, consistent with the notion of neural hyperresponsiveness in this disease.

The effects of Azone and capsaicin on the permeation of naproxen through human skin

The permeation of naproxen through excised human skin and isolated perfused rabbit ear skin has been determined. It was found that both Azone and capsaicin enhanced the permeation with an enhancement ratio of up to 4-fold. The magnitudes of the effect were similar in human and rabbit skin. The permeation of naproxen from a saturated solution of the drug through skin pre-treated with Azone was similar to that from a commercial preparation (Naprosyn). In the perfused rabbit ear experiments the presence of capsaicin had no effect on the vasodilatation of the blood vessels, inferring that the penetration enhancement was a direct result of capsaicin influencing the barrier function of the skin. Structural similarities between Azone and capsaicin were seen using molecular graphics.

Temporal characteristics of capsaicin desensitization and stimulus-induced recovery in the oral cavity

It was recently discovered that capsaicin desensitization of the tongue can be temporarily reversed during recurrent stimulation ("stimulus-induced recovery," SIR). The effects of concentration and the temporal pattern of stimulation on desensitization and SIR were studied in four experiments. In Experiment 1, three different concentrations of capsaicin (3.3, 33, or 330 microM) were delivered to the tongue in blocks of twelve stimuli at the rate of one per minute (treatment block) followed by a block of 20 exposures to 33 microM capsaicin (test block). The 33- and 330-microM treatments both caused significant desensitization, but by the end of the test block recovery was substantial only for the 33-microM condition. Experiment 2 provided a second test of the effect of concentration while also exploring whether intermittent stimulation was a requirement for SIR, i.e., stimuli were refreshed on the tongue every six minutes rather than every 60 s. SIR occurred but was pronounced only when the concentration of the test stimulus equaled or exceeded that of the treatment stimulus. In the third experiment we delivered capsaicin in a candy formulation to examine SIR under conditions in which stimulation was not interrupted at all. Although desensitization was evident during the first few minutes of succeeding exposures to the candy, peak irritation was unchanged throughout nine exposures over 3 days. In the final experiment, we returned to intermittent stimulation to examine the effect of lengthening ISI on SIR. The results showed that SIR remained virtually complete until ISI was lengthened to 60 s. We conclude that SIR is a robust phenomenon that is maximized by rapid exposure to capsaicin in a concentration at least as high as that of the desensitizing stimulus. The implications of these findings for hypotheses about the mechanism of SIR, its function in endogenous chemonociception, and for clinical use of capsaicin as a topical analgesic are discussed.

Non-NSAID pharmacologic treatment options for the management of chronic pain

Chronic pain affects 75 million US citizens. A number of pharmacologic treatments are available for chronic pain that does not respond adequately to nonpharmacologic methods. Long the mainstay of chronic pain management, nonsteroidal anti-inflammatory drugs (NSAIDs) are known to be associated with gastrointestinal (GI) and renal toxicities, a particular problem for the elderly population, which commonly experiences chronic pain, such as that associated with osteoarthritis (OA). Several non-NSAID, non-narcotic therapies are available for noninflammatory pain. Acetaminophen is as effective as NSAIDs for the management of mild-to-moderate OA pain and is the recommended first-line therapy by the American College of Rheumatology (ACR). Propoxyphene, widely believed to be safe and effective, may, in fact, be no more effective-and perhaps less effective-than acetaminophen or ibuprofen. A relatively new analgesic, tramadol, appears to be a useful therapy for patients who do not receive adequate pain relief with acetaminophen and are at risk for NSAID-related side effects. For localized chronic pain associated with OA, topical capsaicin is also an effective analgesic.

Diabetic neuropathy

Better clinical characteristics and a standardized approach to the definition of neuropathy has enabled us to define more precisely the natural history of diabetic neuropathy. Detailed studies on the pathology and pathogenesis have allowed dissection of important pathogenetic pathways. Effective treatment is currently limited, although a number of new and potentially important therapeutic interventions, including modification of the vascular supply and antioxidant status and growth factors, may prove to be of benefit in preventing damage and also promoting repair of peripheral nerves in human diabetic neuropathy.

Review of the effectiveness of capsaicin for painful cutaneous disorders and neural dysfunction

BACKGROUND

Topical capsaicin is known to be a safe and effective pain management adjunct for rheumatoid arthritis, osteoarthritis, neuralgias, and diabetic neuropathy. However, studies and case reports in the literature have indicated that other conditions may also benefit from capsaicin: painful or itching cutaneous disorders from operations, injuries, or tumors; neural dysfunction; or inflammation of the airways and urinary tract.

METHODS

To determine the effectiveness of capsaicin for painful cutaneous disorders and neural dysfunction, the authors analyzed data from 33 reports (MEDLINE search of 1966-96) on the efficacy of capsaicin. Outcome measures consisted of the response rate and degree of pain relief. Results from placebo-controlled trials were pooled when possible; effect of treatment was estimated by the method of DerSimonian and Laird.

RESULTS

Pain relief for postmastectomy syndrome and cluster headache was greater with capsaicin than with placebo; also, psoriasis and pruritus responded better to capsaicin. Uncontrolled studies and case reports have indicated that pain or dysfunction was less at the end of capsaicin therapy for neck pain, loin pain/hematuria syndrome, oral mucositis, rhinopathy, reflex sympathetic dystrophy syndrome, detrusor hyperreflexia, and cutaneous pain due to tumor of the skin.

CONCLUSIONS

Capsaicin is effective for psoriasis, pruritus, and cluster headache; it is often helpful for the itching and pain of postmastectomy pain syndrome, oral mucositis, cutaneous allergy, loin pain/hematuria syndrome, neck pain, amputation stump pain, and skin tumor; and it may be beneficial for neural dysfunction (detrusor hyperreflexia, reflex sympathetic dystrophy, and rhinopathy). A universal problem for many of the studies analyzed was the absence of a "burning placebo" such as camphor.

Topical capsaicin as an adjuvant analgesic for the treatment of traumatic amputee neurogenic residual limb pain

The treatment of amputee residual limb pain can at times be a challenge for the physician. Occasionally, traditional analgesic medication regimens cannot be used or are ineffective in relieving the pain. Topical capsaicin cream has been a beneficial adjuvant medication in the treatment of some painful conditions. The authors present three patients with traumatic upper limb amputations where topical capsaicin cream was of benefit in the treatment of neurogenic residual limb pain. The hope is that these cases will increase awareness of the potential use of capsaicin cream as an adjuvant analgesic in patients with residual limb pain. Common causes of residual limb pain and the pharmacology of capsaicin cream are discussed.

The role of plant-derived drugs and herbal medicines in healthcare

Many of our present medicines are derived directly or indirectly from higher plants. While several classic plant drugs have lost much ground to synthetic competitors, others have gained a new investigational or therapeutical status in recent years. In addition, a number of novel plant-derived substances have entered into Western drug markets. Clinical plant-based research has made particularly rewarding progress in the important fields of anticancer (e.g. taxoids and camptothecins) and antimalarial (e.g. artemisinin compounds) therapies. In addition to purified plant-derived drugs, there is an enormous market for crude herbal medicines. Natural product research can often be guided by ethnopharmacological knowledge, and it can make substantial contributions to drug innovation by providing novel chemical structures and/or mechanisms of action. In the end, however, both plant-derived drugs and crude herbal medicines have to take the same pharmacoeconomic hurdle that has become important for new synthetic pharmaceuticals.

Rapid recovery from capsaicin desensitization during recurrent stimulation

Topical desensitization of the tongue was assessed during multiple bouts of exposure to capsaicin. In the first experiment subjects rated perceived irritation as 30 capsaicin stimuli (33 microM) were applied to the tongue tip in three blocks of 10, with 15 min breaks between blocks. Significant desensitization was measured at the beginning of the second and third blocks within each session. However, as stimulation continued within those blocks sensations of irritation grew toward undesensitized levels ('stimulus-induced recovery' (SIR)). Desensitization did not extend across days. The second experiment employed a 10-fold higher concentration of capsaicin (330 microM) to determine if SIR was limited to low levels of desensitization. SIR occurred as before within sessions, and the higher concentration produced desensitization across days that also exhibited recovery during the first block of stimuli on days 2 and 3. The third experiment included piperine, zingerone and citric acid as stimuli to determine if SIR was specific to capsaicin. Piperine produced SIR under conditions of both self- and cross-desensitization with capsaicin, whereas recovery failed to materialize with zingerone. Citric acid was not significantly cross-desensitized by capsaicin, so recovery could not be measured. Overall the results demonstrate that desensitization of the tongue produced by either capsaicin or piperine can be temporarily reversed if stimulation with either chemical is resumed for only a few minutes. The implications these findings may have for hypotheses about the mechanisms of capsaicin desensitization and sensitization as well as for clinical applications of capsaicin as a topical analgesic are discussed.

Prevalence and characteristics of chronic sensory problems in burn patients

Problems of pain and paresthesia in the healed wounds of burn patients are an understudied and poorly documented phenomenon. This descriptive study was designed to examine the prevalence and characteristics of these chronic sensory problems 1 year or more postburn. Four hundred and thirty patients were sent questionnaires which assessed the frequency and intensity of the problems, influencing factors and impact on patients' lives. These problems were assessed by rating scales (visual analogue and categorical scales) and the McGill Pain Questionnaire (MPQ). The response rate was 67%. Over one-third of the participants (36.4%) complained of pain while the prevalence of paresthetic sensations was 71.2%. More than half of the symptomatic patients experienced sensory problems every week sufficient to interfere with daily living. No relationships were found between these sensory problems and the patients' age or sex, burn etiology, or length of time elapsed since injury. Burn severity was related to the frequency of the problems. Discussion emphasizes the need for adequate treatment of these problems and suggests further research issues.

Peripheral diabetic neuropathy: current concepts in treatment

OBJECTIVE

To review pathophysiology and current concepts in the treatment of diabetic peripheral neuropathy (PN).

DATA SOURCES

References were identified through a MEDLINE search of the English-language literature from 1976 through 1994. Additional references were obtained from reference lists of articles identified through the search.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Clinical trials that involved an adequate number of patients and review articles were selected. Information from articles that was judged by the authors to be significant was selected for discussion.

DATA SYNTHESIS

PN affects 5-50% of people with diabetes in the US and most commonly is characterized by tingling or burning sensations, particularly in the calves, ankles, and feet, with a loss of vibratory sense. Treatment of PN, for the most part, has been unsatisfactory. Therapy has been directed toward either improving nerve function or alleviating symptoms of PN, including pain and paresthesia. Glycemic control may slow the progression of PN. Hyperglycemia also is associated with decreased pain threshold in patients with diabetes mellitus. The aldose reductase inhibitors, particularly tolrestat, have been shown to improve objective and subjective neurologic function. Pain or paresthesia has been treated effectively with antidepressants, lidocaine, mexiletine, and capsaicin. The anticonvulsants phenytoin and carbamazepine may be effective, but are associated with a greater degree of adverse effects. Experimental treatments, such as gamma-linolenic acid, gangliosides, uridine, and the corticotropin4-9 analog ORG 2766, have been effective in improving neurologic function.

CONCLUSIONS

Treatment of PN remains unsatisfactory. Therapy should be directed toward prevention with glycemic control and symptomatic treatment of existing PN.