1. Aetna considers the use of antivirals (oral), capsaicin patch, gabapentin, intra-thecal corticosteroids, lidocaine patch, opioids (oral), pregabalin, and tricyclic anti-depressants medically necessary for post-herpetic neuralgia (PHN). 

2. Aetna considers any the following therapeutic modalities for PHN experimental and investigational because their effectiveness for this indication has not been established (not an all inclusive list):

   1. Acupuncture
   2. Botulinum toxin  
   3. Cryocautery
   4. Dorsal root entry zone lesions/dorsal root ganglion destruction
   5. Epidural corticosteroid or morphine
   6. Intercostal nerve block
   7. Intralesional corticosteroid
   8. Intravenous antiviral therapy
   9. Intravenous ketamine
   10. Intravenous vitamin C
   11. Iontophoresis of vincristine
   12. Laser irradiation
   13. Narrow-band ultraviolet light B
   14. Peripheral nerve stimulation
   15. Stellate ganglion blockade
   16. Sympathectomy
   17. Topical ketamine
   18. Topical piroxicam
   19. Transcutaneous electrical nerve stimulation (TENS).

    For spinal cord stimulation for PHN, see CPB 194 Dorsal Column Stimulation.

3. Aetna considers the use of any of the following pharmacotherapies for the treatment of PHN experimental and investigational because their effectiveness for this indication has not been established (not an all inclusive list):

   1. Biperiden
   2. Carbamazepine
   3. Chlorprothixene
   4. Ganoderma lucidum extract
   5. Nicardipine

See also CPB 0011 - Electrical Stimulation for Pain, CPB 0113 - Botulinum Toxin, CPB 0115 - Varicella and Herpes Zoster Vaccines, CPB 0135 - Acupuncture, and CPB 0194 - Dorsal Column Stimulation.

Herpes zoster (HZ) is the consequence of re-activation of the varicella zoster virus that remains latent since primary infection (varicella). The overall incidence of HZ is about 3 per 1000 of the population per year increasing to 10 per 1000 per year by age 80. Approximately half of persons reaching age 90 years will have had HZ. In approximately 6 %, a second episode of HZ may occur; usually several decades after the first attack. The most common complication of HZ is post-herpetic neuralgia (PHN), defined as significant pain or dysaesthesia present 3 months or more following HZ. More than 5 % of the elderly have PHN at 1 year after acute HZ. Reduced cell-mediated immunity to HZ occurs with aging, which may be responsible for the increased incidence in the elderly and from other causes such as tumors, human immunodeficiency virus infection as well as immunosuppressant drugs. Diagnosis of PHN is usually clinical from typical unilateral dermatomal pain and rash. Prodromal symptoms, pain, itching and malaise, are common (Johnson and Whitton, 2004).

The observation that patients with PHN experience different types of pain (e.g., continuous burning or intense paroxysmal; most often with tactile allodynia) suggests that multiple pathophysiological mechanisms are involved, which may include the peripheral as well as the central nervous systems. Traditional treatments for PHN usually entail tricyclic antidepressants (TCA) such as amitriptyline, nortriptyline, desipramine and maprotiline; antiepileptic drugs such as gabapentin and pregabalin; topical 5% lidocaine patches (Lidoderm), which frequently reduce allodynia; as well as long-acting oral opioid preparations and tramadol (Ultram). Oral antiviral agents (aciclovir, famciclovir, valaciclovir) are used during an acute attack of herpes zoster to prevent postherpetic neuralgia (Wareham, 2006). There is evidence that intrathecal corticosteroids may be effective in patients who are refractory to conservative measures (Wu and Raja, 2008; Hempenstall et al, 2005), but the potential for neurological sequelae should prompt caution with their application (Christo et al, 2007). Epidural corticosteroids have not been shown to provide effective analgesia for PHN (Christo et al, 2007). Many alternative treatments for PHN such as cryocautery, dorsal column (spinal cord) stimulation, iontophoresis of vincristine, intravenous administration of ketamine, an N-methyl-D-aspartate (NMDA) antagonist; laser; peripheral nerve stimulation as well as transcutaneous electrical nerve stimulation (TENS) have not been adequately studied.

Iontophoresis has been suggested to be effective in treating PHN (Ozawa et al, 1999). However, in a randomized controlled trial, Dowd et al (1999) reported that that iontophoresed vincristine is no better than iontophoresed saline in the treatment of this condition. Although TENS has been reported to benefit some patients with PHN (Milligan and Nash, 1985; Robertson and George, 1990), these findings have not been validated by randomized controlled studies. Furthermore, on behalf of the Canadian Coordinating Office for Health Technology Assessment (CCOHTA), Reeve and Corabian (1995) evaluated the scientific evidence of the clinical effectiveness of TENS for the treatment of acute, chronic as well as labor and delivery pain. These researchers concluded that there is little evidence that TENS is effective in treating chronic pain.

In a review on sympathectomy for neuropathic pain, Mailis and Furlan (2003) stated that the practice of surgical and chemical sympathectomy is based on poor quality evidence, uncontrolled studies and anecdotal experience. In addition, complications of the procedure may be significant, in terms of both worsening the pain or producing a new pain syndrome; and abnormal forms of sweating (e.g., compensatory hyperhidrosis and pathological gustatory sweating). The authors concluded that more clinical studies of sympathectomy are needed to establish the potential risks and overall effectiveness of this procedure.

In a pilot study (n = 10), Johnson and Burchiel (2004) found that peripheral nerve stimulation of the supra-orbital or infra-orbital branches of the trigeminal nerve is effective in relieving trigeminal neuropathic pain following facial trauma or herpetic infection. These investigators stated that a prospective clinical trial using this novel approach to treat these disorders is thus warranted. A recent Cochrane review (Mailis-Gagnon et al, 2004) on spinal cord stimulation (SCS) concluded that although there is limited evidence in favor of SCS for failed back surgery syndrome and complex regional pain syndrome (also known as reflex sympathetic dystrophy), more research is needed to confirm whether SCS is an effective treatment for other types of chronic pain. Gilden et al (2005) noted that because only a few studies have used antiviral therapy to manage PHN and with conflicting results, larger, double-blind studies, which give intravenous antiviral drug, are needed. Thus, well-designed, multi-center, controlled clinical trials are needed to ascertain the effectiveness of various alternative treatments in the treatment of PHN.

An earlier systematic review of randomized controlled trials on treatments for PHN (Volmink et al, 1996) reported that pooled analysis of the effect of TCA demonstrated statistically significant pain relief. Pooling of the results of the 3 studies comparing the effects of capsaicin and placebo could not be performed due to heterogeneity, which was mainly attributable to an unpublished trial which differed in terms of the dosage and duration of treatment. When this study was omitted, no heterogeneity was found and the pooled analysis revealed a statistically significant benefit. However, problems with blinding in patients using capsaicin may have accounted for the positive effect. One small study of iontophoresis of vincristine compared to placebo yielded a favorable result. Other therapies evaluated included lorazepam, acyclovir, topical benzydamine as well as acupuncture. There was no evidence that these treatments are effective in relieving pain associated with PHN. These investigators concluded that based on evidence from randomized trials, TCA appear to be the only agents of proven benefit for established PHN.

A more recent evidence-based report on treatment of PHN was developed by the Quality Standards Subcommittee of the American Academy of Neurology (Dubinsky et al, 2004) and it had the following recommendations:

1. Acupuncture, benzydamine cream, dextromethorphan, indomethacin, epidural methylprednisolone, epidural morphine sulfate, iontophoresis of vincristine, lorazepam, vitamin E and zimelidine are not of benefit.
2. Aspirin cream or ointment is possibly effective in the relief of pain in patients with PHN but the magnitude of benefit is low, as is seen with topical capsaicin.
3. The effectiveness of carbamazepine, nicardipine, biperiden, chlorprothixene, ketamine, Helium:Neon (He:Ne) laser irradiation, intralesional triamcinolone, cryocautery, topical piroxicam, extract of Ganoderma lucidum, dorsal root entry zone lesions and stellate ganglion block are unproven in the treatment of PHN.
4. Tricyclic antidepressants, gabapentin, pregabalin, opioids and lidocaine patch are effective and should be used in the treatment of PHN.

In a multi-center, randomized controlled study, van Wijck and colleagues (2006) reported that a single epidural injection of 80 mg methylprednisolone and 10 mg bupivacaine within the first days of herpes zoster has a modest effect in reducing zoster-associated pain for one month; however there were no significant differences in pain level between the two groups at subsequent follow-ups. At 1 month, 137 (48 %) patients in the epidural group (plus standard therapy given to the control group) reported pain compared with 164 (58 %) in the control group (oral antivirals and analgesics). After 3 months these values were 58 (21 %) and 63 (24 %) respectively, and at 6 months, 39 (15 %) and 44 (17 %). The main drawback of this study was that it was neither double-blinded nor placebo-controlled, which decreased the validity of the already modest anti-nociceptive effects of the treatment within the first month. Moreover, this treatment is ineffective in preventing the development of long-term PHN. Furthermore, Baron and Wasner (2006) stated that large, well-designed prospective studies are needed to estimate the preemptive effect of neuropathic pain treatment on PHN.

In a Cochrane review, Khaliq et al (2007) examined the safety and effectiveness of topical lidocaine in the treatment of PHN. The investigators identified three trials meeting inclusion criteria, involving 182 topical lidocaine treated participants and 132 control participants. Two trials gave data on pain relief, and the remaining study provided data on secondary outcome measures. The largest trial compared topical lidocaine patch to a placebo patch and accounted for 150 of the 314 patients included in the analysis. A meta-analysis combining two of the three studies identified a significant difference between the topical lidocaine and control groups for the primary outcome measure -- a mean improvement in pain relief according to a pain relief scale. Topical lidocaine relieved pain better than placebo (p = 0.003). The investigators also found a statistical difference between the groups for the secondary outcome measure of mean visual analog scale (VAS) score reduction (p = 0.03), but only for a single small trial. In the selected studies, there were a similar number of adverse skin reactions in both treatment and placebo groups. The investigators reported that the highest recorded blood lidocaine concentration varied between 59 ng/ml and 431 ng/ml between trials. The investigators noted that the latter figure is high and posited that it may have been due to contamination of the sample during the assay procedure.

Christo et al (2007) stated that epidural corticosteroids have not been shown to provide effective analgesia for PHN.  Furthermore, Wu and Raja (2008) stated that the majority of interventional therapies show equivocal analgesic efficacy although some data indicate that intrathecal methylprednisolone may be effective.  The author stated that further randomized, controlled trials will be needed to confirm the analgesic efficacy of analgesic and interventional therapies (e.g., sympathetic nerve blocks/other nerve blocks, intrathecal methylprednisolone, and spinal cord stimulation) to determine their role in the overall treatment of patients with PHN.

In a Cochrane review, He et al (2008) examined the efefctiveness of corticosteroids in preventing PHN. People of all ages with herpes zoster of all degrees of severity within 7 days after onset were included. Interventions include corticosteroids given by oral, intramuscular or intravenous routes during the acute stage (starting within 1 week of onset of the rash) compared with no treatment or placebo, but not with other treatments. Primary outcome measure was the presence of PHN 6 months after the onset of the acute herpetic rash. Secondary outcome measure was pain severity measured by a validated VAS or numerical descriptive scale after 3, 6 and 12 months; quality of life measured with the Short Form 36 questionnaire after 6 months; adverse events during or within 2 weeks after stopping treatment. Five trials were included with altogether 787 participants. All were randomized, double-blind, placebo-controlled parallel group studies. There was no significant difference between the corticosteroid and control groups for the primary outcome (RR 1.27, 95 % confidence interval [CI]: 0.20 to 7.97). There was also no significant difference between the corticosteroid plus anti-viral agents and placebo plus anti-viral agents groups for the primary outcome (RR 0.90, 95 % CI: 0.40 to 2.03). No included trials evaluated pain severity with a validated VAS or numerical descriptive scale and also no trials measured quality of life with the Short Form 36 questionnaire. Adverse events during or within 2 weeks after stopping treatment were reported by all 5 included trials, but after meta-analysis, there was no significant difference in any serious adverse event (e.g., death, acute cardiac insufficiency, rash dissemination, bacterial pneumonia or hematemesis) or non-serious adverse event (e.g., dizziness, nausea, vomiting, hypertension or hyperglycemia). The authors concluded that there was insufficient evidence that corticosteroids are safe or effective in the prevention of PHN. They stated that more randomized controlled trials with a greater number of participants are needed to determine reliably whether there is real benefit (or harm) from the use of corticosteroid therapy to prevent PHN; and that future trials should measure function and quality of life.

A Clinical Evidence systematic evidence review concluded that corticosteroids for post-herpetic neuralgia are likely to be ineffective or harmful in preventing post-herpetic neuralgia (Wareham, 2006). The evidence review noted that, not only have corticosteroids not been proven to be effective for this indication, but they may cause dissemination of herpes zoster.

Chau et al (2007) evaluated the outcome of pain treatment for the elderly patients with PHN. A total of 58 elderly outpatients with PHN were studied. The pain intensity before and after treatment were assessed by patients themselves with numeric pain scale (NPS). The pain treatment included (i) medication with anti-convulsants, opioids and non-steroidal anti-inflammatory drugs (NSAIDs); (ii) nerve block with 0.25 % bupivacaine or 1 % lidocaine twice-weekly at the beginning of the treatment. The therapeutic outcome was expressed by pain relief. The reduction of pain and residual pain intensity were evaluated subjectively by the patients themselves with patients' global impression and NPS, respectively, after treatment for 1 and 3 months (or last visit). The adverse events throughout the treatment course were analyzed. The mean age of the patients was 75.1 years. The number of female PHN sufferers was higher than that of male in all aged groups and the highest incidence was found in the age group of 70 to 79 (65.5 %). The most commonly involved dermatomes were in the thoracic region (82.7 %). All patients suffered from severe pain (NPS 8 to 10) before treatment. The pain management was a combination of medication and nerve block at the beginning of the treatment. Among the medications, gabapentin was prescribed to all the patients and almost all of them (98.3 %) required opioids simultaneously and some of them needed additional NSAIDs at the beginning of the treatment. The most common adverse event was somnolence (24.1 %). Among the sympathetic blocks, the intercostal nerve block was performed commonly (84.5 %). The therapeutic outcome was expressed by pain relief. As to the reduction of pain, 46 cases (79.3 %) and 57 cases (98.3 %) felt moderate and much improvement after treatment for 1 and 3 months (or last visit), respectively. As to residual pain intensity, although none of them got complete pain relief, there were 12 cases (20.7 %) and 45 cases (77.6 %) felt the pain intensity was mild (NPS 1 to 3) after treatment for 1 and 3 months respectively. There was a statistically significant decrease in the pain intensity between before treatment and after treatment for 1 month and 3 months. The authors concluded that these findings showed that the concurrent combination therapy with proper medications and appropriate nerve blocks could offer satisfactory pain relief in the majority of elderly patients with PHN. The effect of intercostal nerve block is confounded by the concomitant use of pain medications.

Schencking and associates (2010) reported the findings of intravenous administration of vitamin C in the treatment of 2 patients with PHN. These 2 subjects (females aged 67 and 53 years) were from an average and unselected patient group of a general practice with confirmed acute herpetic neuralgia who were observed in the course of their illness. They received the basic analgesic (according to the WHO step scheme) and viral-static therapy. Furthermore, 15-g of vitamin C was administered intravenously every second day over a period of 2 weeks. Sudden and total remission of the neuropathic pain (measured on the basis of VAS) could be observed. Remission of the cutaneous lesions was noted within 10 days. The use of the vitamin C appears to be an interesting component of alternative therapeutic strategies in the treatment of HZ. Especially for therapy-resistant cases of PHN, vitamin C administration should be examined as an additional option. The authors concluded that to test and confirm these clinical findings, randomized clinical trials regarding the use of vitamin C in the concomitant treatment of zoster-associated neuralgia should be performed.

In a randomized, double-blind study, Backonja et al (2008) examined the safety and effectiveness of one application of NGX-4010, a high-concentration (8 %) capsaicin dermal patch, in the treatment of patients with PHN. A total of 402 patients were randomly assigned to one 60-min application of NGX-4010 (640 microg/cm(2) or a low-concentration capsaicin control patch (3.2 microg/cm(2) [0.04 % capsaicin]). Patients were aged 18 to 90 years, had had PHN for at least 6 months, and had an average baseline numeric pain rating scale (NPRS) score of 3 to 9. The primary efficacy end point was percentage change in NPRS score from baseline to weeks 2 to 8. Analysis was by intention-to-treat. Patients who were randomly assigned to NGX-4010 (n = 206) had a significantly greater reduction in pain during weeks 2 to 8 than did patients who had the control patch (n = 196). The mean changes in NPRS score were -29.6 % versus -19.9 % (difference -9.7 %, 95 % CI: -15.47 to -3.95; p = 0.001). A total of 87 (42 %) patients who received NGX-4010 and 63 (32 %) controls had a 30 % or greater reduction in mean NPRS score (odds ratio [OR] 1.56, 95 % CI: 1.03 to 2.37; p = 0.03). Patients who had NGX-4010 had significant improvements in pain during weeks 2 to 12 (mean change in NPRS score -29.9 % versus -20.4 %, difference -9.5, -15.39 to -3.61; p = 0.002). Transient blood pressure changes associated with changes in pain level were recorded on the day of treatment, and short-lasting erythema and pain at the site of application were common, self-limited, and generally mild-to-moderate in the NGX-4010 group and less frequent and severe in the controls. The authors concluded that one 60-min application of NGX-4010 provided rapid and sustained pain relief in patients with PHN. No adverse events were associated with treatment except for local reactions at the site of application and those related to treatment-associated pain.

In a Cochrane review, Derry et al (2009) reviewed the evidence from controlled trials on the efficacy and tolerability of topically applied capsaicin in chronic neuropathic pain in adults. Randomized, double-blind, placebo-controlled studies of at least 6 weeks' duration, using topical capsaicin to treat neuropathic pain were included in this analysis. A total of 6 studies (389 participants in total) compared regular application of low dose (0.075 %) capsaicin cream with placebo cream; the numbers needed to treat to benefit (NNT) for any pain relief over 6 to 8 weeks was 6.6 (4.1 to 17). Two studies (709 participants in total) compared a single application of high dose (8 %) capsaicin patch with placebo patch; the NNT for greater than or equal to 30 % pain relief over 12 weeks was 12 (6.4 to 70). Local skin reactions were more common with capsaicin, usually tolerable, and attenuated with time; the numbers needed to treat to harm (NNH) for repeated low dose application was 2.5 (2.1 to 3.1). There were insufficient data to analyse either data set by condition or outcome definition. All studies satisfied minimum criteria for quality and validity, but maintenance of blinding remains a potential problem. The authors concluded that capsaicin, either as repeated application of a low dose (0.075 %) cream, or a single application of a high dose (8 %) patch may provide a degree of pain relief to some patients with painful neuropathic conditions. Local skin irritation, which is often mild and transient but may lead to withdrawal, is common. Systemic adverse effects are rare. Estimates of benefit and harm are not robust due to limited amounts of data for different neuropathic conditions and inconsistent outcome definition.

In a randomized, double-blind, controlled study with an open-label extension, Backonja et al (2010) evaluated the safety, effectiveness and tolerability of NGX-4010 in patients with PHN. Patients were randomized to receive NGX-4010 or control patch in a 4-week, double-blind study. This was followed by an open-label extension phase (up to 48 weeks total) where patients could receive up to 3 additional treatments no sooner than 12 weeks after initial treatment. The primary efficacy variable was mean change from baseline in mean morning and evening NPRS scores. During days 8 to 28 after the double-blind treatment, NGX-4010 patients had a mean change in NPRS scores from baseline of -32.7 % compared with -4.4 % for control patients (p = 0.003). Mean NPRS scores decreased from baseline during week 1 in both treatment groups, remained relatively stable through week 12 in NXG-4010 patients, but returned to near baseline during weeks 2 to 4 in controls. Mean change in NPRS scores from baseline during weeks 2 to 12 was -33.8 % for NGX-4010 and +4.9 % for control recipients. A similar decrease in NPRS scores from baseline was maintained with subsequent NGX-4010 treatments, regardless of the number of treatments received. Transient increases in application site pain were adequately managed with analgesics. No increases in application site reactions or adverse events were observed with repeated treatments. No patients discontinued the study due to an adverse event. The authors concluded that NGX-4010 is a promising topical treatment for PHN patients, which appears to be tolerable, generally safe, and effective.

In an open-label study, Simpson and associates (2010) assessed the safety of repeated applications of NGX-4010 over 1 year in patients with moderate to severe PHN or human immunodeficiency virus-associated distal sensory polyneuropathy (HIV-DSP). Patients had successfully completed a previous NGX-4010 study and had a pain level appropriate for further treatment. Eligible patients had not been treated with NGX-4010 within 12 weeks of study initiation. Patients received pre-treatment with a topical local anesthetic (lidocaine 4 %) for 60 minutes followed by either a 60-minute (PHN and HIV-DSP patients) or a 90-minute (HIV-DSP patients) treatment with NGX-4010. Patients could receive up to 3 additional treatments at intervals of greater than or equal to 12 weeks. Regardless of the number of treatments received, all patients were followed-up for 48 weeks except for those withdrawing early. A total of 106 patients were enrolled and received a total of 293 NGX-4010 treatments. The most frequently reported treatment-emergent adverse events were transient, mild-to-moderate application site erythema, pain, edema, and papules. Small, transient pain-related increases in blood pressure during and immediately after NGX-4010 application were observed. There was no evidence of an increased incidence of adverse events, dermal irritation, intolerability, or impaired neurological function with repeated treatments. The authors concluded that repeated treatments with NGX-4010 administered over a 1-year period are generally safe and well-tolerated.

McCormack (2010) stated that capsaicin dermal patch is an adhesive patch containing a high concentration (8 % w/w) of synthetic capsaicin. It is indicated in the European Union for the treatment of peripheral neuropathic pain in non-diabetic adults using a single 30- or 60-minute application repeated every 90 days, as required, and in the United States for the treatment of neuropathic pain associated with PHN. In pivotal, randomized, double-blind, multi-center trials in adults with PHN, a single 60-minute application of capsaicin dermal patch reduced the mean NPRS scores from baseline to a significantly greater extent than a low-concentration (0.04 % w/w capsaicin) control patch during weeks 2 to 8. In randomized, double-blind, multi-center trials in patients with HIV-associated neuropathy, capsaicin dermal patch reduced the mean NPRS scores from baseline significantly more than control in 1 study for the 30- and 90-minute, but not the 60-minute, application during weeks 2 to 12. In another study, the differences between capsaicin (30- and 60-minute applications) and control did not reach statistical significance. An integrated analysis of both studies showed that the 30-minute application of capsaicin dermal patch was significantly better than control for the reduction from baseline in mean NPRS scores during weeks 2 to 12. The efficacy of capsaicin dermal patch was maintained for up to 1 year in extension studies in which patients could receive up to 3 or 3 repeat treatments. Capsaicin dermal patch was generally well-tolerated in clinical trials. The most common adverse events were transient, mostly mild-to-moderate, application-site reactions.

On November 16, 2009, the Food and Drug Administration approved Qutenza (capsaicin, 8 % patch) for the treatment of the pain associated with PHN. Qutenza must be applied to the skin by a health care professional since placement of the patch can be quite painful, requiring use of a local topical anesthetic, as well as additional pain relief such as ice or use of opioid pain relievers. The patient must also be monitored for at least 1 hour since there is a risk of a significant rise in blood pressure following patch placement. The product insert of Qutenza states that the patches should be applied to the most painful skin areas, using up to 4 patches.  Furthermore, the patches should be applied for 60 minutes and repeat every 3 months or as warranted by the return of pain (not more frequently than every 3 months).

In a pilot study, Nabarawy et al (2011) evaluated the effect of narrow-band ultra-violet light B (nbUVB) in the treatment PHN.  The study included 17 patients with distressing PHN.  Patients were evaluated using the Verbal Rating Scale (VRS).  They received nbUVB sessions, 3 times a week, for a total of 15 sessions or until the pain disappeared.  Patients were followed-up for a period of 3 months after the end of therapy.  Using intention-to-treat analysis, more than 50 % improvement was achieved in 6 (35.29 %) and 8 (47.06 %) patients, at the end of therapy and after 3 months follow-up, respectively.  An improvement of less than 50 % was achieved in 11 (64.71 %) and 9 (52.94 %) patients, at the end of therapy and after 3 months follow-up, respectively.  The pain severity assessed by the VRS significantly improved both at the end of sessions (p = 0.005) and after 3 months follow-up (p = 0.005).  The authors concluded that nbUVB may be of beneficial use in the treatment of PHN.  The drawbacks of this pilot study were small number of patients and limited follow-up period.  These preliminary findings need to be validated by well-designed studies.

Barros et al (2012) stated that herpes zoster infection may cause PHN.  This phenomenon may be reversed by (S)-ketamine (SKET), but its use results in intolerable side effects, while its topical administration seems to be safe.  In a cross-over study, these researchers examined the effectiveness of topical (S)-ketamine for pain management of PHN.  A total of 12 patients were randomly divided into 2 groups.  There was a significant effect of time on pain intensity, but no statistical difference in pain scores for SKET or placebo use in this sample in this treatment regimen.  Only few mild cutaneous reactions were observed with topical SKET use.