How should zoster trials be conducted?

Diagnosis and assessment of pain associated with herpes zoster and postherpetic neuralgia

Accurate evaluation of pain plays a critical role in identifying new interventions for the treatment and prevention of herpes zoster and postherpetic neuralgia (PHN). Different types of pain and other sensory symptoms are found in patients with herpes zoster, and these vary greatly with respect to their presence, location, duration, intensity, and quality. The results of recent studies of herpes zoster and PHN and the development of new methods for assessing neuropathic pain provide a foundation for diagnosing and assessing the pain associated with herpes zoster. We review the results of recent research to identify the essential components that must be considered in developing an evidence-based description of pain associated with herpes zoster and PHN.

PERSPECTIVE

Comprehensive assessments of pain are necessary for clinical research on the epidemiology, natural history, pathophysiologic mechanisms, treatment, and prevention of pain in herpes zoster and PHN.

Predicting postherpetic neuralgia in elderly primary care patients with herpes zoster: prospective prognostic study

Postherpetic neuralgia (PHN) is the most frequent complication of herpes zoster (HZ) and difficult to treat. Timely identification of high-risk HZ-patients enables physicians to focus on PHN prevention. To assess which simple to measure factors are independent predictors of PHN, and whether psychosocial and serological/virological parameters have additional predictive value, a prospective cohort study in primary care was conducted. We included 598 elderly (>50 years) consecutive patients with acute HZ (rash <7 days) below sixth cervical dermatome. At baseline demographic, clinical (e.g., duration and severity of pain and rash), psychological (Pain Cognition List [PCL] and Spielberger's Anxiety Inventory), serological (VZV-antibodies) and virological (viremia presence) variables were measured. Blood tests were performed in a random subset of 218 patients. Primary outcome was significant pain (VAS >30 on 0-100 scale) after three months. The final prediction model obtained from multivariable logistic regression was (internally) validated using bootstrapping techniques, and adjusted for optimism. Forty-six (7.7%) patients developed PHN. Independent predictors were age (odds ratio [OR]=1.08 per year), acute pain severity (OR=1.02 per unit), presence of severe rash (OR=2.31), and rash duration before consultation (OR=0.78 per day): area under receiver-operating-characteristic curve [ROC area]=0.77 (95% CI: 0.71-0.82). Of the five PCL scores, only factor V ('trust in healthcare') was an additional predictor (OR=1.01 per unit), though it increased the ROC area with only 0.01 to 0.78. The Spielberger's anxiety scores and serological and virological variables were no additional predictors. Thus, four simple variables can help physicians to timely identify elderly HZ-patients at risk of PHN.

Natural history of pain following herpes zoster

In a longitudinal observational study of 94 patients (39 M:55 F, mean age 69) at elevated risk for developing post herpetic neuralgia (PHN), the natural history of pain during the first 6 months after herpes zoster (HZ) rash onset was determined. Pain severity and impact were rated using pain-VAS, SF-MPQ, and MPI. Applying a definition of PHN of average daily pain >0/100 on the pain VAS during the last 48 h, 30 subjects had PHN at 6 months. These 30 subjects reported more pain and a higher SF-MPQ score (p<0.01) at study inclusion than the 64 subjects whose pain completely resolved by 6 months. At 6 months, mean daily pain in the PHN group was 11/100 (95% CI 5,16) and only nine of these subjects were still taking prescription medication for HZ pain. The rate of recovery (pain severity over time) was the same in the PHN and no-pain groups. At study inclusion, the SF-MPQ and MPI scores in our PHN group were similar to historical controls with chronic severe PHN enrolled in clinical trials, but by 6 months the scores in our PHN subjects were significantly lower than historic controls. Only two subjects met the more stringent criteria for 'clinically meaningful' PHN at 6 months (> or = 30/100 on the pain VAS). Defining PHN as average daily pain >0/100 at 6 months after rash onset appears to substantially overestimate the number of HZ patients negatively impacted by ongoing pain and disability.

Brivudin compared with famciclovir in the treatment of herpes zoster: effects in acute disease and chronic pain in immunocompetent patients. A randomized, double-blind, multinational study

OBJECTIVE

This was a double-blind, randomized multicentre trial comparing efficacy and safety of brivudin (125 mg, once a day) and famciclovir (250 mg, three times a day), both given orally for 7 days, in the treatment of herpes zoster.

METHODS

A total of 2027 immunocompetent zoster patients>or=50 years with zoster-related pain at presentation were included. Outcome measures embraced prevalence of postherpetic neuralgia (PHN), defined as at least moderate pain 3 months after treatment initiation, duration of PHN, prevalence and duration of zoster-associated pain (ZAP), duration of vesicle formation and rash healing.

RESULTS

The prevalence of PHN at month 3 was 11.3% with brivudin and 9.6% with famciclovir [per-protocol (PP) population]. Equivalence of the two drugs could be demonstrated (P=0.01, PP and intention-to-treat analysis). The median duration of PHN was 46.5 days with brivudin and 58 days with famciclovir (P=0.54, PP analysis). Prevalence and duration of ZAP did not differ significantly between treatment groups. The prevalence of PHN was higher in patients>or=65 years (brivudin: 16.4%, famciclovir: 16.4%), and in patients with severe rash (brivudin: 13.4%, famciclovir: 15.7%), without significant differences between treatment groups. In patients>or=65 years, median duration of PHN was shorter with brivudin than with famciclovir (39.5 vs. 57.5 days), although the difference was not statistically significant. The two drugs had equivalent efficacy in being able to accelerate the stop of vesicle formation, and lesion healing. Adverse events were similar in nature and prevalence among groups.

CONCLUSIONS

The study demonstrated equivalent efficacy of brivudin and famciclovir in the treatment of herpes zoster regarding the prevention of chronic pain and the resolution of signs and symptoms of acute herpes zoster. Compared with famciclovir, brivudin provides equivalent efficacy and safety at a more convenient once-daily dose schedule.

The role of antivirals in the management of neuropathic pain in the older patient with herpes zoster

Herpes zoster has been known since ancient times. It is a ubiquitous disease, occurring sporadically without any seasonal preference and is caused by the varicella-zoster virus. It may be defined as an endogenous relapse of the primary infection varicella. Herpes zoster is characterised by typical efflorescences in the innervation region of a cranial or spinal nerve and starts and ends with pain of varying intensity. Currently, several antiviral drugs are approved and many studies have shown that antiviral therapy, started early in the course of disease, can significantly reduce the risk and the duration of postherpetic neuralgia in elderly patients. The effects of all antivirals discussed in this article, given either orally or intravenously, are comparable with regards to the resolution of virus replication, prevention of dissemination of skin lesions and reduction of acute herpes zoster pain. Valaciclovir (valacyclovir), famciclovir and brivudine (brivudin) are comparably effective in the reduction of the incidence and/or prevention of zoster-associated pain and postherpetic neuralgia. Brivudine 125mg once daily is as effective as famciclovir 250mg three times daily in reducing the prevalence and the duration of zoster-associated pain and postherpetic neuralgia, especially if therapy is combined with a structured-pain therapy. The intensity of the therapy for pain should depend on the intensity of the pain that it is treating. Famciclovir and brivudine offer an advantage over other antivirals because they are administered less frequently; this is particularly relevant for elderly patients who may already be taking a number of medications for other diseases. Therefore, antiviral therapy in combination with adequate pain management should be given to all elderly patients as soon as herpes zoster is diagnosed.

The PINE study: rationale and design of a randomised comparison of epidural injection of local anaesthetics and steroids versus care-as-usual to prevent postherpetic neuralgia in the elderly [ISRCTN32866390]

BACKGROUND: Postherpetic neuralgia (PHN) is by far the most common complication of herpes zoster (HZ) and one of the most intractable pain disorders. Since PHN is seen most often in the elderly, the number of patients with this disorder is expected to increase in our ageing society. PHN may last for months to years and has a high impact on the quality of life. The results of PHN treatment are rather disappointing. Epidural injection of local anaesthetics and steroids in the acute phase of HZ is a promising therapy for the prevention of PHN. Since randomised trials on the effectiveness of this intervention are lacking, the PINE (Prevention by epidural Injection of postherpetic Neuralgia in the Elderly) study was set up. The PINE study compares the effectiveness and cost-effectiveness of a single epidural injection of local anaesthetics and steroids during the acute phase of HZ with that of care-as-usual (i.e. antivirals and analgesics) in preventing PHN in elderly patients. METHODS / DESIGN: The PINE study is an open, multicenter clinical trial in which 550 elderly (age >/= 50 yr.) patients who consult their general practitioner in the acute phase of HZ (rash < 7 days) are randomised to one of the treatment groups. The primary clinical endpoint is the presence of HZ-related pain one month after the onset of the rash. Secondary endpoints include duration and severity of pain, re-interventions aiming to treat the existing pain, side effects, quality of life, and cost-effectiveness. CONCLUSION: The PINE study is aimed to quantify the (cost-) effectiveness of a single epidural injection during the acute phase of HZ on the prevention of PHN.

Oral antivirals revisited in the treatment of herpes zoster: what do they accomplish?

Oral antiviral agents currently represent the most important therapeutic keystone in the treatment of herpes zoster. Three oral antiviral agents are available for the treatment of herpes zoster: acyclovir, its derivative valacyclovir, and famciclovir. Meta-analysis of published data has shown that oral acyclovir significantly reduces various herpes zoster-related symptoms as well as the duration, intensity and prevalence of zoster-associated pain (ZAP). However, this drug does not influence postherpetic neuralgia. The newer agents famciclovir and valacyclovir exhibit a better oral bioavailability than acyclovir. These agents have demonstrated similar efficacy to acyclovir with ZAP and they require less frequent administration. When initiated within 72 hours, oral antiviral therapy of herpes zoster is beneficial in selected, elderly immunocompetent patients, reducing the duration and intensity of ZAP and providing more rapid skin lesion healing. Oral antivirals are also of benefit in immunocompromised patients with uncomplicated herpes zoster. However, signs of cutaneous and visceral dissemination should be monitored; if signs occur, intravenous antiviral therapy is indicated.

Understanding pain in herpes zoster: an essential for optimizing treatment

After herpes zoster, immunocompetent persons frequently experience chronic pain and considerable suffering. Zoster-associated pain has a complex pathophysiology that begins with viral damage and increased sensitization of peripheral sensory neurons. The enhanced afferent barrage from these neurons sensitizes spinal neurons and leads to loss of synapses from descending inhibitory fibers, resulting in central neuropathic pain and allodynia. Antiviral therapy of acute zoster limits this sequence of pathophysiologic mechanisms. There is no clear consensus regarding the optimal means of determining the benefits of antiviral therapy in the management of pain of herpes zoster. A novel statistical approach utilizing rates of disappearance of pain of differing pathophysiologic mechanisms is proposed.

Clinical applications for change-point analysis of herpes zoster pain

Pain is the most frequent and disabling complication of herpes zoster. The analysis of pain severity data is complicated by the nonlinear rate of resolution. Further, three distinct phases characterize pain resolution--acute, subacute, and chronic. Using two clinical trial datasets as the bases for analyses, the rates of baseline pain resolution were computed across each of three phases and compared for age, severity of pain at onset, and number of lesions at baseline. The results defined transition points of 24.4 +/- 3.34 for the subacute phase and 110.3 +/- 11.9 days for the chronic phase. The model demonstrated a treatment effect of valiciclovir (VACV) during the subacute phase as compared to acyclovir (ACV) (P = 0.006) and supports effects of age, baseline pain and number lesions on pain cessation rates in the acute phase. This model verifies three phases of zoster pain and delineates the impact of treatment and other factors on the phase-specific rates of pain cessation.

Phase specific analysis of herpes zoster associated pain data: a new statistical approach

Herpes zoster or shingles is a frequent occurrence in both elderly individuals and immunocompromised hosts. The pain associated with herpes zoster is the most debilitating complication of the disease. It can be described as acute pain and post-herpetic neuralgia or zoster associated pain (ZAP). The latter definition encompasses pain from the onset of disease through its resolution and provides a convenient analytic tool for evaluation of antiviral therapy. A heuristic examination of ZAP historical data suggests the existence of three phases of pain resolution: the acute, subacute and chronic phases. The subacute and chronic phases comprise the post-herpetic neuralgia (PHN) stage. Common analytic methods, such as a Kaplan-Meier survival function or a Cox's model, have been used to assess the pain. However, such approaches do not adequately allow for phase comparison. Notably, in the clinical trial setting the comparison of specific treatment effects on the latter stages of pain are of the greatest medical relevance since this is the most debilitating phase of the illness. In order to incorporate the phase-specific information in the modelling of time to cessation of ZAP, we assumed the hazard function was a stepwise constant. Utilizing the full likelihood function, we obtained the maximum likelihood estimate for the transition times (that is, change-points), and other parameters of medical importance. The standard error of the change-point estimates were obtained through a bootstrapping method. The asymptotic properties of the parameter estimates are also discussed. Hence, the rates of pain resolution across all phases can be examined in order to precisely define the existence of multiple phases. In addition, the covariates effect can be examined across phases and populations, thereby allowing us to translate potential efficacy of a standard therapy to different populations. These results can be utilized in the design of clinical trials or in targeting the outcome for a specific phase while controlling for the effect of other variables.

The role of sympathetic nerve blocks in herpes zoster and postherpetic neuralgia

The most common complication of herpes zoster in immunocompetent patients is postherpetic neuralgia (PHN). Sympathetic blocks have been traditionally used for patients with herpes zoster and PHN with three different therapeutic goals: pain relief during acute herpes zoster, pain relief during PHN, and prevention of PHN by treating patients with acute zoster. The role of sympathetic blocks in herpes zoster and PHN remains controversial due to methodologic shortcomings in published studies and the limited current understanding of the role of the sympathetic nervous system in mediating pain. Current theories of the pathophysiology of PHN, the role of the sympathetic nervous system in herpes zoster and PHN, and published studies investigating use of sympathetic nerve blocks in herpes zoster and PHN are reviewed.

Valaciclovir: a review of its use in the management of herpes zoster

Varicella zoster virus (VZV), the pathogen responsible for herpes zoster, belongs to the herpesvirus family and is sensitive to the antiviral drug aciclovir. However, the low oral bioavailability of aciclovir has to some extent limited its efficacy in the treatment of herpes zoster and has prompted the development of the more readily absorbed oral prodrug valaciclovir. In a large comparative study valaciclovir, (1000 mg 3 times daily for 7 days) was at least as effective as aciclovir (800 mg 5 times daily for 7 days) in controlling the symptoms of acute herpes zoster. Importantly, valaciclovir alleviated zoster-associated pain and postherpetic neuralgia significantly faster than aciclovir. A 14-day regimen of valaciclovir showed no significant advantage over the 7-day regimen. A smaller trial in Japanese patients focusing primarily on the cutaneous (rash) signs of herpes zoster confirmed the similar efficacy of valaciclovir and aciclovir in the 7-day regimen. This study did not follow all patients for a formal analysis of postherpetic neuralgia. Valaciclovir and aciclovir demonstrated similar efficacy for the control of cutaneous lesions and ocular complications in patients with zoster ophthalmicus. Preliminary results of a large controlled trial indicate that valaciclovir 1000 mg 3 times daily and famciclovir (the prodrug of penciclovir) 500 mg 3 times daily are of similar efficacy in speeding resolution of acute herpes zoster rash and shortening the duration of postherpetic neuralgia. Starting treatment later than 72 hours after rash onset did not significantly reduce the beneficial effect of valaciclovir on duration of zoster-associated pain (a continuum of pain that encompasses both acute pain and postherpetic neuralgia) in a large observational study, suggesting that valaciclovir might be effective when given later than previously thought. However, valaciclovir should ideally be given as soon as possible after symptoms appear. With the recommended regimen for the treatment of herpes zoster (1000 mg 3 times daily for 7 days) valaciclovir was well tolerated, with nausea and headache being the most commonly reported adverse events. The adverse events profile of the agent was similar to that seen with aciclovir or famciclovir.

CONCLUSION

The efficacy of valaciclovir for the treatment of herpes zoster has been confirmed and extended by follow-up studies in herpes zoster ophthalmicus, in Japanese patients, and in the wider primary care setting. Valaciclovir is at least equivalent to, and better in certain parameters than, aciclovir and appears to have similar efficacy to famciclovir 500 mg 3 times daily. Valaciclovir is a well tolerated first-line therapy with an established place in the treatment of immunocompetent patients with herpes zoster.

Pain and its Assessment in Herpes Zoster

Pain typically accompanies acute herpes zoster. In a proportion of patients, herpes zoster pain persists well beyond rash healing. This persisting pain is termed post-herpetic neuralgia (PHN). Because of the substantial personal and economic burdens caused by PHN, studies of the pathophysiology of herpes zoster pain and of the efficacy of antiviral treatment in reducing prolonged pain are of great importance. Different methods have been used to examine pain in research on herpes zoster and in clinical trials, making it difficult to compare across studies. There is substantial evidence, however, that demonstrates the importance of distinguishing acute pain from PHN. Several differences have been found between acute herpes zoster pain and PHN, including pathophysiological findings, risk factors and pain quality. Recommendations for the design and analysis of future trials of antiviral agents in herpes zoster have been recently proposed. These include a definition of PHN and recommended secondary end points for future trials. Adopting these recommendations in future research on herpes zoster pain, and in the design and analysis of future trials, will facilitate comparisons across studies of the pathophysiology and prevention of PHN.

The management of postherpetic neuralgia

Postherpetic neuralgia is defined as pain persisting, or recurring, at the site of shingles at least three months after the onset of the acute rash. Thus defined, at least half of shingles sufferers over the age of 65 years develop postherpetic neuralgia. In addition to increasing age, less important risk factors for postherpetic neuralgia are pain severity of acute shingles and trigeminal distribution. Postherpetic neuralgia accounts for 11-15% of all referrals to pain clinics and would, in fact, be far more effectively dealt with in primary care. Effective treatment of acute shingles by systemic antivirals at the appropriate time may have some effect in reducing the incidence of postherpetic neuralgia, making it easier to treat with tricyclics and greatly reducing scarring (25% of all cases affect the face). Pre-emptive treatment with low-dose tricyclics (ami- or nor-triptyline 10-25 mg nocte) from the time of diagnosis of acute shingles reduces the incidence of postherpetic neuralgia by about 50%. Established postherpetic neuralgia should be vigorously treated with adrenergically active tricyclics in a dose rising over two or three weeks from 10-25 mg to 50-75 mg. Positive relaxation should also be used. Carbamazepine, like conventional analgesics, is of little or no value. Failure of tricyclics to effect relief within eight weeks calls for specialist treatment. North American practitioners in particular believe that some opioids (e.g., oxycodone) may be helpful in otherwise intractable cases.

Assessment of pain in herpes zoster: lessons learned from antiviral trials

Pain typically accompanies acute herpes zoster and, in a proportion of patients, it persists well beyond rash healing. Pain must therefore be analyzed in trials of antiviral agents in herpes zoster, but different methods have been used to analyze pain in recent published trials. These reports are reviewed and their methodological strengths and weaknesses examined. Based on this review, recommendations for the design and analysis of future trials of antiviral agents in herpes zoster are proposed. The principal recommendation is that antiviral efficacy should be evaluated both by distinguishing post-herpetic neuralgia from acute pain and by considering pain as a continuum. The primary endpoint should address both the prevalence and duration of post-herpetic neuralgia and should be examined in those patients who have post-herpetic neuralgia. Adopting the proposed recommendations in design and analysis of future trials should facilitate comparison across trials of the efficacy of antiviral agents in the treatment of herpes zoster.

Pain and its persistence in herpes zoster

The nature and duration of pain associated with herpes zoster is highly variable. This review of research on pain in acute herpes zoster and postherpetic neuralgia (PHN) explores those observations relevant to the definition and pathogenesis of PHN and the design of treatment trials. A model for the pathogenesis of PHN is presented, which gains support from studies of risk factors. Several directions for future research are identified.