Recognition and treatment of shingles

Synthesis of Fluorinated Nucleosides/Nucleotides and Their Antiviral Properties

The FDA has approved several drugs based on the fluorinated nucleoside pharmacophore, and numerous drugs are currently in clinical trials. Fluorine-containing nucleos(t)ides offer significant antiviral and anticancer activity. The insertion of a fluorine atom, either in the base or sugar of nucleos(t)ides, alters its electronic and steric parameters and transforms the lipophilicity, pharmacodynamic, and pharmacokinetic properties of these moieties. The fluorine atom restricts the oxidative metabolism of drugs and provides enzymatic metabolic stability towards the glycosidic bond of the nucleos(t)ide. The incorporation of fluorine also demonstrates additional hydrogen bonding interactions in receptors with enhanced biological profiles. The present article discusses the synthetic methodology and antiviral activities of FDA-approved drugs and ongoing fluoro-containing nucleos(t)ide drug candidates in clinical trials.

Selected nucleos(t)ide-based prescribed drugs and their multi-target activity

Nucleos(t)ide analogues play pivotal roles as antiviral, cytotoxic or immunosuppressive agents. Here, we review recent reports of nucleoside analogues that exhibit broad-spectrum activity towards multiple life-threatening RNA and DNA viruses. We also present a discussion about nucleoside antimetabolites-approved antineoplastic agents-that have recently been shown to have antiviral and/or antibacterial activity. The approved drugs and drug combinations, as well as recently identified candidates for investigation and/or experimentation, are discussed. Several examples of repurposed drugs that have already been approved for use are presented. This strategy can be crucial for the first-line treatment of acute infections or coinfections and for the management of drug-resistant strains.

Revisiting childhood herpes zoster

Herpes zoster is rare in otherwise healthy children, but it is more common in association with immunosuppression. Maternal varicella infection during pregnancy and varicella occurring in the newborn represent risk factors for childhood herpes zoster. However, some controversies persist about risk factors, diagnosis, and the natural history of childhood disease. In a 2-year prospective study, 18 children with herpes zoster were clinically diagnosed in outpatient consultations in a hospital dermatology unit. Data about age, dermatome involvement, underlying disease, and history of previous varicella were recorded. Tzanck smears, biopsy specimens, and sera were obtained from 18, 4, and 10 children, respectively. The varicella zoster virus major envelope glycoprotein gE was detected in 16 of 18 smears and all four biopsies. Herpes simplex virus I was demonstrated in one of the smears. The established risk factors for childhood herpes zoster were only found in one child. Evidence for previous full-blown varicella and varicella with few lesions was recorded in 7 and 4 of the 17 immunocompetent children, respectively. No history of varicella was recalled in 6 of 17 cases, although a serologic clue of past varicella infection (IgM negative, IgG positive) was disclosed. Recurrent herpes zoster was diagnosed in one immunocompromised child. Zoster-associated pain was localized and the disease severity remained mild in all children. Established risk factors for childhood herpes zoster were only rarely found in our series of patients. In contrast, unrecognized varicella and varicella with few lesions were frequently recorded and may represent additional risk factors for shingles in childhood. Zosteriform herpes simplex virus infections should be differentiated from childhood herpes zoster, emphasizing the importance of precise viral identification.

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.

Antiviral therapies for herpes zoster infections. Are they economically justifiable?

Antiviral treatment of herpes zoster is controversial because of uncertain benefits and relatively high costs. Most studies show that antiviral therapy lessens acute herpes zoster symptoms and postherpetic neuralgia (PHN). Current clinical recommendations support antiviral treatment of severely symptomatic herpes zoster in all adults, and mild herpes zoster in those 50 or 60 years of age or older. However, it is unclear if these recommended strategies are cost effective. Published studies of herpes zoster costs and the effect of antiviral therapy on costs and quality of life have significant variation in study design and results, as well as many shortcomings in the data. Thus, definitive economic recommendations cannot be made based on the present data. Another approach, which we have used, is to develop a 'reference case' analysis using decision-analysis techniques and the available data to estimate the incremental cost effectiveness of antiviral treatment in patients of differing age and herpes zoster severity. In the baseline analysis, parameter values and assumptions were consistently slightly biased against antiviral use. Effectiveness was measured in quality-adjusted life years (QALYs). We assumed that antiviral treatment did not change PHN risk, but decreased PHN duration in patients older than 50 years. PHN risk increased with age and with acute herpes zoster severity as seen in published data. Mild acute herpes zoster was assumed to have a utility value of 0.9 and severe acute herpes zoster a value of 0.7 on a scale where 0 = death and 1 = perfect health. Treating mildly symptomatic acute herpes zoster cost $US89,200/QALY gained in 40-year-olds, $US47,700/QALY in 60-year-olds and $US40,700/QALY in 70-year-olds (1995 values). Results were most sensitive to variation of antiviral costs (baseline $US134), but changes in acute symptom relief, PHN risk, duration, costs and utility, and antiviral effect on PHN duration increased costs/QALY above $US50,000 in 60- and 70-year-olds in extremes of parameter ranges. However, no variation resulted in treatment of mild illness in 40-year-olds to fall below $US50,000/QALY gained. Treatment of severe acute herpes zoster cost $US29,700, $US18,000 and $US16,500/QALY gained in 40-, 60- and 70-year-olds, respectively. Results were sensitive to variation of antiviral costs (> $US225) and acute symptom relief (< 21%) in 40-year-olds. Based on this analysis, antiviral therapy of herpes zoster seems economically justifiable for mildly symptomatic acute herpes zoster in patients aged 50 years and older, and for severely symptomatic acute herpes zoster in all adults.

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.

Chronic verrucous varicella zoster virus skin lesions: clinical, histological, molecular and therapeutic aspects

The outbreak of HIV infection introduced a new phenomenon in varicella zoster virus (VZV) pathology, namely the long-standing wart-like skin lesions that are frequently associated with resistance to thymidine kinase (TK)-dependent antiviral agents. This paper reviews the clinical, histological, and molecular aspects and the therapeutic management of these verrucous lesions. The majority of lesions are characterized by chronically evolving, unique or multiple wart-like cutaneous lesions. The main histopathological features include hyperkeratosis, verruciform acanthosis and VZV-induced cytopathic changes with scant or absent cytolysis of infected keratinocytes. The mechanism that establishes the chronic nature of the lesions appears to be associated with a particular pattern of VZV gene expression exhibiting reduced or nondetectable gE and gB synthesis. Drug resistance to TK-dependent antiviral agents is a result of nonfunctional or deficient viral TK. This necessitates alternative therapeutic management using antiviral agents that target the viral DNA polymerase.

Current pharmacological approaches to the therapy of varicella zoster virus infections: a guide to treatment

Varicella zoster virus (VZV), a member of the herpesvirus family, is responsible for both primary (varicella, chickenpox) as well as reactivation (zoster, shingles) infections. In immunocompetent patients, the course of varicella is generally benign. For varicella zoster, post-herpetic neuralgia is the most common complication. In immunocompromised patients (particularly those with AIDS), transplant recipients and cancer patients, VZV infections can be life-threatening. For these patients and also for immunocompetent patients at risk such as pregnant women or premature infants, the current treatment of choice is based on either intravenous or oral aciclovir (acyclovir). The low oral bioavailability of aciclovir, as well as the emergence of drug-resistant virus strains, have stimulated efforts towards the development of new compounds for the treatment of individuals with VZV infections. Among these new compounds, penciclovir, its oral prodrug form famciclovir and the oral pro-drug form of aciclovir (valaciclovir), rank among the most promising. As with aciclovir itself, all of these drugs are dependent on the virus-encoded thymidine kinase (TK) for their intracellular activation (phosphorylation), and, upon conversion to their triphosphate form, they act as inhibitors/alternative substrate of the viral DNA polymerase. Therefore, cross-resistance to these drugs may be expected for those virus mutants that are TK-deficient and thus resistant to aciclovir. Other classes of nucleoside analogues dependent for their phosphorylation on the viral TK that have been pursued for the treatment of VZV infections include sorivudine, brivudine, fialuridine, fiacitabine and netivudine. Among oxetanocins, which are partially dependent on viral TK, lobucavir is now under clinical evaluation. Foscarnet, which does not require any previous metabolism to interact with the viral DNA polymerase, is used in the clinic when TK-deficient VZV mutants emerge during aciclovir treatment. TK-deficient mutants are also sensitive to the acyclic nucleoside phosphonates (i.e. [s]-1-[3-hydroxy-2-phosphonylmethoxypropyl]cytosine; HPMPC); these agents do not depend on the virus-encoded TK for their phosphorylation but depend on cellular enzymes for conversion to their diphosphoryl derivatives which then inhibit viral DNA synthesis. Vaccination for VZV has now come of age. It is recommended for healthy children, patients with leukaemia, and patients receiving immunosuppressive therapy or those with chronic diseases. The protection induced by the vaccine seems, to some extent, to include zoster and associated neuralgia. Passive immuniatin based on specific immunoglobulins does not effectively prevent VZV infection and is therefore restricted to high risk individuals (i.e. immunocompromised children and pregnant women).

Herpes zoster in children

BACKGROUND

The clinical studies of series of children with herpes zoster (HZ) are rather limited.

OBJECTIVE

The purpose of this study was to evaluate the epidemiologic conditions, clinical manifestations, therapy, and outcome of HZ in children.

METHODS

Twenty-one patients with HZ have been studied. Five patients who had herpes simplex virus infection were excluded. The laboratory diagnosis was made by fluorescent techniques. Acyclovir was administered systematically for 2 more days after no new lesions had developed.

RESULTS

Thirteen patients (group A) were immunocompromised; eight patients (group B) were otherwise healthy. Two patients from group B had intrauterine varicella; the other six patients had had varicella under the age of 4 years. Three patients were recently exposed to varicella. The duration of HZ was significantly longer in group A than in group B, but the outcome was good in all patients.

CONCLUSION

Herpes simplex virus infection may simulate the pattern of HZ; varicella in early childhood is a risk factor for HZ in otherwise healthy children; exposure of a child to varicella may cause reactivation of latent HZ virus; and acyclovir therapy within 3 days of exanthem onset prevents significant morbidity and death in immunocompromised children with HZ.

[Zona in children]

Herpes zoster is the clinical consequence of a late reactivation of the varicella zoster virus (VZV). It infects mainly the elderly, but pediatric cases are not uncommon. It occurs mostly in immunocompromised children, or in infancy after reactivation of latent VZV infection acquired transplacentally during intrauterine life. Rarely, herpes zoster occurs in otherwise normal children, especially following varicella during the first year of life. Clinical presentation of herpes zoster in children is identical to that of adult, with usually a benign course. The impairment of cellular and non specific immunity (Natural Killer cells) appears to have a particular role in the occurrence of herpes zoster. Treatment of the usual form comprises antiseptic measures and prevention of pruritus. In immunocompromised children, the infection is generally severe and disseminated, and can result in high rates of morbidity and mortality, thus requiring specific intravenous antiviral therapy with antiviral drugs such as acyclovir without delay. There is no single approach towards VZV infection prevention in immunocompromised hosts. Vaccination with live attenuated varicella vaccine, has proved to be efficient and safe in immunocompromised children.

Herpes zoster in childhood: case report and review of the literature

Herpes zoster in childhood is uncommon even in the setting of known risk factors such as primary varicella zoster infection before 12 months of age and immunocompromised states. We report a 7-year-old, otherwise healthy girl with shingles, and review the risk factors, prognosis, and treatment of pediatric zoster.

Acyclic nucleosides as antiviral compounds

Acyclovir is an effective drug for the treatment of HSV and VZV infections, which after phosphorylation to the triphosphate, inhibits viral DNA polymerase. Acyclovir has low oral bioavailability, therefore prodrugs have been developed, and the L-valyl ester, valaciclovir, recently has been licensed for the treatment of shingles. Ganciclovir is used against CMV, and famciclovir, a lipophilic prodrug of penciclovir, is marketed for shingles. The acyclic nucleoside phosphonates are active against thymidine kinase-resistant viral strains. Promising analogs are PMEA (in clinical trial for the treatment of AIDS) and (S)-HPMPC (good in vivo activity against HSV, VZV, CMV, and EBV). Oligonucleotides incorporating acyclic nucleosides at the 3'-and 5'-ends, or constituted of amino acyclic nucleosides, are resistant to cleavage by nucleases and may be useful in antisense and/or antigene therapy. HEPT is active against HIV-1: It binds in a hydrophic pocket on reverse transcriptase, rather than in the polymerase active site. Some acyclic nucleosides are potent inhibitors of purine and pyrimidine nucleoside phosphorylase. These compounds may have a therapeutic niche in combination therapy with antiviral and anticancer nucleosides, and in the treatment of diseases involving the T-cell.

Immunohistochemical identification of varicella-zoster virus gene 63-encoded protein (IE63) and late (gE) protein on smears and cutaneous biopsies: implications for diagnostic use

Early and specific recognition of varicella zoster virus (VZV) infection is of vital concern in immunocompromised patients. The aim of this study was to compare the diagnostic accuracy of histochemical and immunohistochemical identification of the VZV ORF63 encoded protein (IE63) and of the VZV late protein gE on smears and formalin-fixed paraffin-embedded skin sections taken from lesions clinically diagnosed as varicella (n = 15) and herpes zoster (n = 51). Microscopic examinations of Tzanck smears and skin sections yielded a diagnostic accuracy of Herpesviridae infections in 66.7% (10/15) and 92.3% (12/13) of varicella, and 74.4% (29/39) and 87.8% (43/49) of herpes zoster, respectively. Immunohistochemistry applied to varicella provided a type-specific virus diagnostic accuracy of 86.7% (13/15; IE63) and 100% (15/15; gE) on smears, and of 92.3% for both VZV proteins on skin sections. In herpes zoster, the diagnostic accuracy of immunohistochemistry reached 92.3% (36/39; IE63) and 94.9% (37/39; gE) on smears, and 91.7% (44/48; IE63) and 91.8% (45/49; gE) on skin sections. These findings indicate that the immunohistochemical detection of IE63 and gE on both smears and skin sections yields a higher specificity and sensitivity than standard microscopic assessments.