Foscarnet therapy in five patients with AIDS and acyclovir-resistant varicella-zoster virus infection

Varicella-Zoster Virus Prevalence among Pregnant Women: A European Epidemiological Review

Europe has faced a massive spread of the varicella-zoster virus through the years. Since the introduction of an effective vaccine, complications and severe forms of chickenpox have been restricted. Nevertheless, among the population, some categories need specific care, such as pregnant women, who present one of the most fragile conditions facing this infection, both for the mother and the fetus. In this review, we highlight how the varicella-zoster virus can be dangerous during pregnancy, underlining the problem of treatment and vaccination, and collect information about the European epidemiology among this particular category of women.

An Autopsy Case of Disseminated Varicella Zoster Virus Infection during the Treatment of Nephrotic Syndrome

A 68-year-old woman developed systemic blisters while receiving treatment for nephrotic syndrome. As she also developed marked liver dysfunction and disseminated intravascular coagulation, she was admitted to our hospital. She was diagnosed with varicella zoster virus (VZV) infection. Treatment was administered in the intensive-care unit, but the patient died on day 24 post-admission after severe VZV infection. A post-mortem examination showed micro-abscesses and necrosis caused by varicella zoster infection in multiple organs, including the liver, kidneys, and gastrointestinal tract. Because VZV infection can become severe in immunocompromised patients, careful consideration is needed for the prevention and treatment of the viral infection.

Emergence of varicella-zoster virus resistance to acyclovir: epidemiology, prevention, and treatment

Introduction: Acyclovir has led to the development of successful systemic therapy for herpes simplex virus and varicella-zoster virus (VZV) infection, and the use of valacyclovir and famciclovir has improved treatment. Additionally, the use of a helicase-primase (HP) inhibitor (HPI), amenamevir, is changing the treatment of herpes zoster (HZ).Area covered: VZV infection is prevented by vaccines and is treated with antiviral agents. Acyclovir and penciclovir are phosphorylated by viral thymidine kinase and work as chain terminators. Improvements in the management of immunocompromised patients have reduced severe and prolonged immunosuppression and chronic VZV infection with acyclovir-resistant mutants has become rarer. The HP is involved in the initial step of DNA synthesis and amenamevir has novel mechanisms of action, efficacy to acyclovir-resistant mutants, and pharmacokinetic characteristics. The literature search for PUBMED was conducted on 10 April 2020 and updated on 4 November 2020.Expert opinion: Amenamevir has been used to treat HZ in Japan. Although the number of patients with VZV infection will decrease owing to the use of vaccines, the addition of HPI will improve treatment and treatment options for resistant viruses. The clinical use of HPIs in addition to current nucleoside analogs opens a new era of antiherpes therapy.

Advances and Perspectives in the Management of Varicella-Zoster Virus Infections

Varicella-zoster virus (VZV), a common and ubiquitous human-restricted pathogen, causes a primary infection (varicella or chickenpox) followed by establishment of latency in sensory ganglia. The virus can reactivate, causing herpes zoster (HZ, shingles) and leading to significant morbidity but rarely mortality, although in immunocompromised hosts, VZV can cause severe disseminated and occasionally fatal disease. We discuss VZV diseases and the decrease in their incidence due to the introduction of live-attenuated vaccines to prevent varicella or HZ. We also focus on acyclovir, valacyclovir, and famciclovir (FDA approved drugs to treat VZV infections), brivudine (used in some European countries) and amenamevir (a helicase-primase inhibitor, approved in Japan) that augur the beginning of a new era of anti-VZV therapy. Valnivudine hydrochloride (FV-100) and valomaciclovir stearate (in advanced stage of development) and several new molecules potentially good as anti-VZV candidates described during the last year are examined. We reflect on the role of antiviral agents in the treatment of VZV-associated diseases, as a large percentage of the at-risk population is not immunized, and on the limitations of currently FDA-approved anti-VZV drugs. Their low efficacy in controlling HZ pain and post-herpetic neuralgia development, and the need of multiple dosing regimens requiring daily dose adaptation for patients with renal failure urges the development of novel anti-VZV drugs.

Viral ribonucleotide reductase attenuates the anti-herpes activity of acyclovir in contrast to amenamevir

Amenamevir is a helicase-primase inhibitor of herpes simplex virus (HSV) and varicella-zoster virus (VZV) and is used for the treatment of herpes zoster in Japan. The half maximal effective concentrations (EC₅₀s) of acyclovir and sorivudine for VZV increased as the time of treatment was delayed from 6 to 18 h after infection, while those of amenamevir and foscarnet were not affected. Susceptibility of infected cells at 0 and 18 h after infection was examined with four anti-herpes drugs, and the fold increases in EC₅₀ for acyclovir, sorivudine, amenamevir, and foscarnet were 13.1, 6.3, 1.3, and 1.0, respectively. The increase in the EC₅₀s for acyclovir in the late phase of infection in VZV and HSV was abolished by hydroxyurea, a ribonucleotide reductase (RR) inhibitor. The common mechanism affecting antiviral activities of acyclovir to HSV and VZV was examined in HSV-infected cells. The amount of HSV DNA in cells treated with amenamevir at 10 x EC₅₀ was similar at 0 and 12 h but less than that in cells treated with acyclovir at 10 x EC₅₀. dGTP, produced through viral RR, peaked at 4 h and decreased thereafter as it was consumed by viral DNA synthesis. Because acyclovir and amenamevir inhibited viral DNA synthesis, thus making dGTP unnecessary, dGTP was significantly more abundant in the presence of acyclovir and amenamevir than in untreated, infected cells. Abundant dGTP supplied by RR may compete with acyclovir triphosphate and attenuate its antiviral activity. In contrast, abundant dGTP did not influence the inhibitory action of amenamevir on viral helicase-primase activity. ATP was significantly decreased at 12 h after infection and significantly more abundant in untreated infected cells compared to cells treated with acyclovir and amenamevir. The anti-herpetic activity of amenamevir was not affected by the replication cycle of VZV and HSV, indicating the suitability of amenamevir for the treatment of herpes zoster and suppressive therapy for genital herpes.

[S2k guideline for the diagnosis and therapy of zoster and post-zoster neuralgia]

Diese Leitlinie richtet sich an Dermatologen, Ophthalmologen, HNO-Ärzte, Pädiater, Neurologen, Virologen sowie Infektiologen, Anästhesisten und Allgemeinmediziner in Klinik und Praxis und dient zur Information für andere medizinische Fachrichtungen, die an der Behandlung des Zoster beteiligt sind. Darüber hinaus soll die Leitlinie Kostenträgern und politischen Entscheidungsträgern zur Orientierung dienen. Die Leitlinie wurde im formellen Konsensusverfahren (S2k) von Dermatologen, Virologen/Infektiologen, Ophthalmologen, HNO-Ärzten, Neurologen, Pädiatern und Anästhesisten/Schmerzmedizinern erstellt.

Die Leitlinie stellt einen Überblick über die klinische und molekulare Diagnostik sowie den Antigennachweis, die Antikörperkultur und Viruskultur dar. Diagnostisch besondere Situationen und komplizierte Verläufe der Erkrankung finden ebenfalls Berücksichtigung. Die antivirale Therapie des Zoster und der Postzosterneuralgie wird im Allgemeinen und für besondere Situationen dargelegt. Detaillierte Angaben zur Schmerzbehandlung finden Erwähnung und sind in einer Übersicht dargestellt. Ebenso werden die lokaltherapeutischen Maßnahmen thematisiert.

Differences in the Likelihood of Acyclovir Resistance-Associated Mutations in the Thymidine Kinase Genes of Herpes Simplex Virus 1 and Varicella-Zoster Virus

Acyclovir (ACV) resistance-associated mutations in two recombinant herpes simplex virus 1 (HSV-1) clones were compared. Recombinant HSV-1 lacking its thymidine kinase (TK) and expressing varicella-zoster virus (VZV) TK ectopically had no mutations in the VZV TK gene. In contrast, recombinant HSV-1 expressing HSV-1 TK ectopically harbored mutations in the HSV-1 TK gene. These results suggest that the relatively low frequency of ACV-resistant VZV is a consequence of the characteristics of the TK gene.

Antiviral resistance in herpes simplex virus and varicella-zoster virus infections: diagnosis and management

PURPOSE OF REVIEW

Aciclovir (ACV) is the first-line drug for the management of herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Long-term administration of ACV for the treatment of severe infections in immunocompromised patients can lead to the development of drug resistance. Furthermore, the emergence of isolates resistant to ACV is increasingly recognized in immunocompetent individuals with herpetic keratitis. This review describes the mechanisms involved in drug resistance for HSV and VZV, the laboratory diagnosis and management of patients with infections refractory to ACV therapy.

RECENT FINDINGS

Genotypic testing is more frequently performed for the diagnosis of infections caused by drug-resistant HSV or VZV isolates. Molecular biology-based systems for the generation of recombinant viruses have been developed to link unknown mutations with their drug phenotypes. Fast and sensitive methods based on next-generation sequencing will improve the detection of heterogeneous viral populations of drug-resistant viruses and their temporal changes during antiviral therapy, which could allow better patient management. Novel promising compounds acting on targets that differ from the viral DNA polymerase are under clinical development.

SUMMARY

Antiviral drug resistance monitoring for HSV and VZV is required for a rational use of antiviral therapy in high-risk populations.

European consensus-based (S2k) Guideline on the Management of Herpes Zoster - guided by the European Dermatology Forum (EDF) in cooperation with the European Academy of Dermatology and Venereology (EADV), Part 1: Diagnosis

Herpes zoster (HZ, shingles) is a frequent medical condition which may severely impact the quality of life of affected patients. Different therapeutic approaches to treat acute HZ are available. The aim of this European project was the elaboration of a consensus-based guideline on the management of patients who present with HZ, considering different patient populations and different localizations. This interdisciplinary guideline aims at an improvement of the outcomes of the acute HZ management concerning disease duration, acute pain and quality of life of the affected patients and at a reduction of the incidence of postherpetic neuralgia and other complications. The guideline development followed a structured and predefined process, considering the quality criteria for guidelines development as suggested by the AGREE II instrument. The steering group was responsible for the planning and the organization of the guideline development process (Division of Evidence based Medicine, dEBM). The expert panel was nominated by virtue of clinical expertise and/or scientific experience and included experts from the fields of dermatology, virology/infectiology, ophthalmology, otolaryngology, neurology and anaesthesiology. Recommendations for clinical practice were formally consented during the consensus conference, explicitly considering different relevant aspects. The guideline was approved by the commissioning societies after an extensive internal and external review process. In this first part of the guideline, diagnostic means have been evaluated. The expert panel formally consented recommendations for the management of patients with (suspected) HZ, referring to the assessment of HZ patients, considering various specific clinical situations. Users of the guideline must carefully check whether the recommendations are appropriate for the context of intended application. In the setting of an international guideline, it is generally important to consider different national approaches and legal circumstances with regard to the regulatory approval, availability and reimbursement of diagnostic and therapeutic interventions.

European consensus-based (S2k) Guideline on the Management of Herpes Zoster - guided by the European Dermatology Forum (EDF) in cooperation with the European Academy of Dermatology and Venereology (EADV), Part 2: Treatment

Herpes zoster (HZ, shingles) is a frequent medical condition which may severely impact the quality of life of affected patients. Different therapeutic approaches to treat acute HZ are available. The aim of this European project was the elaboration of a consensus-based guideline on the management of patients who present with HZ, considering different patient populations and different localizations. This interdisciplinary guideline aims at an improvement of the outcomes of the acute HZ management concerning disease duration, acute pain and quality of life of the affected patients and at a reduction in the incidence of postherpetic neuralgia (PHN) and other complications. The guideline development followed a structured and pre-defined process, considering the quality criteria for guidelines development as suggested by the AGREE II instrument. The steering group was responsible for the planning and the organization of the guideline development process (Division of Evidence-Based Medicine, dEBM). The expert panel was nominated by virtue of clinical expertise and/or scientific experience and included experts from the fields of dermatology, virology/infectiology, ophthalmology, otolaryngology, neurology and anaesthesiology. Recommendations for clinical practice were formally consented during the consensus conference, explicitly considering different relevant aspects. The guideline was approved by the commissioning societies after an extensive internal and external review process. In this second part of the guideline, therapeutic interventions have been evaluated. The expert panel formally consented recommendations for the treatment of patients with HZ (antiviral medication, pain management, local therapy), considering various clinical situations. Users of the guideline must carefully check whether the recommendations are appropriate for the context of intended application. In the setting of an international guideline, it is generally important to consider different national approaches and legal circumstances with regard to the regulatory approval, availability and reimbursement of diagnostic and therapeutic interventions.

Progress in the Clinical Management of Herpesvirus Infections

Antiviral drug discovery has produced a series of drugs active against herpesviruses in vitro. Several of these are now licensed and/or have been used in clinical practice. This article reviews the mechanisms of action of acyclovir, ganciclovir, penciclovir, sorivudine and foscarnet, the development of resistance to these drugs and their pharmacokinetic and cellular toxicities. Based upon the natural histories of HSV, VZV and CMV, treatment objectives for each virus are discussed and the performance of each drug matched against these objectives. Overall, it is concluded that the perfect drug for treating herpesviruses does not exist, but that significant progress has been made towards controlling several herpesvirus diseases. It is suggested that further progress will require not just improved drug discovery programmes, but also an understanding of different pathogeneses and an appreciation by practising physicians that antiviral drugs must be given early in the infectious process to achieve the best results.

Varicella-zoster virus infections - antiviral therapy and diagnosis

Varicella-zoster virus is an important human pathogen that causes varicella after primary infection and zoster after recurrence. Following primary infection, the virus remains latently for life in dorsal root and cranial nerve ganglia. Varicella and zoster are worldwide widespread diseases and may be associated with significant complications. This manuscript presents a short overview about the fundamental knowledge including the most important clinical signs, the capabilities for antiviral treatment and the spectrum of methods for laboratory diagnosis.

Diagnosis, antiviral therapy, and prophylaxis of varicella-zoster virus infections

Varicella-zoster virus (VZV), an important member of the Herpesviridae family, is the etiological agent of varicella as primary infection and zoster as recurrence. An outstanding feature is the lifelong viral latency in dorsal root and cranial nerve ganglia. Both varicella and zoster are worldwide widespread diseases that may be associated with significant complications. However, there is a broad spectrum of laboratory methods to diagnose VZV infections. In contrast to many other viral infections, antiviral treatment of VZV infections and their prevention by vaccination or passive immunoprophylaxis are well established in medical practice. The present manuscript provides an overview about the basic knowledge of VZV infections, their laboratory diagnosis, antiviral therapy, and the prevention procedures, especially in Germany.

Advances in the management of viral infections

Viral infections are common in cancer patients. The risk and severity of infection are influenced by patient, disease, treatment, and viral factors. Severe viral infections are more likely to occur in treatment regimens that are more immunosuppressive. Historically, the most frequent severe infections have been due to herpesviruses, but more recently, other pathogens, especially community respiratory and hepatitis viruses, have received increasing attention as major viral pathogens in cancer patients. Because of the new diagnostic assays and the introduction of better therapeutic options, knowledge of viral infections is important in optimizing antineoplastic therapies.

Advances in the treatment of varicella-zoster virus infections

Varicella-zoster virus (VZV) causes two distinct diseases, varicella (chickenpox) and shingles (herpes zoster). Chickenpox occurs subsequent to primary infection, while herpes zoster (usually associated with aging and immunosuppression) appears as a consequence of reactivation of latent virus. The major complication of shingles is postherpetic neuralgia. Vaccination strategies to prevent varicella or shingles and the current status of antivirals against VZV will be discussed in this chapter. Varivax®, a live-attenuated vaccine, is available for pediatric varicella. Zostavax® is used to boost VZV-specific cell-mediated immunity in adults older than 50 years, which results in a decrease in the burden of herpes zoster and pain related to postherpetic neuralgia. Regardless of the availability of a vaccine, new antiviral agents are necessary for treatment of VZV infections. Current drugs approved for therapy of VZV infections include nucleoside analogues that target the viral DNA polymerase and depend on the viral thymidine kinase for their activation. Novel anti-VZV drugs have recently been evaluated in clinical trials, including the bicyclic nucleoside analogue FV-100, the helicase-primase inhibitor ASP2151, and valomaciclovir (prodrug of the acyclic guanosine derivative H2G). Different candidate VZV drugs have been described in recent years. New anti-VZV drugs should be as safe as and more effective than current gold standards for the treatment of VZV, that is, acyclovir and its prodrug valacyclovir.

The use of antiviral drugs during the neonatal period

Parenteral therapy of viral infections of the newborn and infant began with vidarabine (adenine arabinoside) for the treatment of neonatal herpes simplex virus (HSV) infections in the early 1980s. Acyclovir has become the treatment of choice for neonatal HSV infections and a variety of other herpesvirus infections. Ganciclovir is beneficial for the treatment of congenital cytomegalovirus (CMV) infections involving the central nervous system (CNS). This article reviews the use of acyclovir and ganciclovir in the treatment of neonatal HSV and congenital CMV infections. A brief summary precedes a detailed discussion of available established and alternative therapeutics.

In vitro-selected drug-resistant varicella-zoster virus mutants in the thymidine kinase and DNA polymerase genes yield novel phenotype-genotype associations and highlight differences between antiherpesvirus drugs

Varicella zoster virus (VZV) is usually associated with mild to moderate illness in immunocompetent patients. However, older age and immune deficiency are the most important risk factors linked with virus reactivation and severe complications. Treatment of VZV infections is based on nucleoside analogues, such as acyclovir (ACV) and its valyl prodrug valacyclovir, penciclovir (PCV) as its prodrug famciclovir, and bromovinyldeoxyuridine (BVDU; brivudin) in some areas. The use of the pyrophosphate analogue foscarnet (PFA) is restricted to ACV-resistant (ACV(r)) VZV infections. Since antiviral drug resistance is an emerging problem, we attempt to describe the contributions of specific mutations in the viral thymidine kinase (TK) gene identified following selection with ACV, BVDU and its derivative BVaraU (sorivudine), and the bicyclic pyrimidine nucleoside analogues (BCNAs), a new class of potent and specific anti-VZV agents. The string of 6 Cs at nucleotides 493 to 498 of the VZV TK gene appeared to function as a hot spot for nucleotide insertions or deletions. Novel amino acid substitutions (G24R and T86A) in VZV TK were also linked to drug resistance. Six mutations were identified in the "palm domain" of VZV DNA polymerase in viruses selected for resistance to PFA, PCV, and the 2-phophonylmethoxyethyl (PME) purine derivatives. The investigation of the contributions of specific mutations in VZV TK or DNA polymerase to antiviral drug resistance and their impacts on the structures of the viral proteins indicated specific patterns of cross-resistance and highlighted important differences, not only between distinct classes of antivirals, but also between ACV and PCV.

Emerging drugs for varicella-zoster virus infections

INTRODUCTION

Varicella-zoster virus (VZV) is the etiological agent of two distinct diseases, varicella (chickenpox) and shingles (herpes zoster). Chickenpox occurs following primary infection, while herpes zoster (usually associated with ageing and immunosuppression) is the consequence of reactivation of the latent virus. Post-herpetic neuralgia is the major complication of shingles.

AREAS COVERED

This review will discuss vaccination strategies and the current status of antivirals against VZV. A live attenuated vaccine, Varivax, is available for pediatric varicella while Zostavax was developed to boost VZV-specific cell-mediated immunity in adults older than 60 years and, via this mechanism, to decrease the burden of herpes zoster and pain associated with post-herpetic neuralgia. Despite the availability of a vaccine, there is a need for new antiviral agents. Current drugs approved for the treatment of VZV infections include nucleoside analogs that target the viral DNA polymerase and depend on the viral thymidine kinase. Novel anti-VZV drugs have recently been evaluated in clinical trials, including the bicyclic nucleoside analog FV-100, the helicase-primase inhibitor ASP2151 and valomaciclovir (prodrug of the acyclic guanosine derivative H2G).

EXPERT OPINION

New anti-VZV drugs should be as safe as and more effective than acyclovir and its prodrug valacyclovir (current gold standard for the treatment of VZV).

Resistance testing of clinical varicella-zoster virus strains

Acyclovir resistance of varicella-zoster virus (VZV) has been reported in rare cases of immunocompromised patients. In this study, the natural polymorphism of the thymidine kinase (TK) and DNA polymerase (pol) genes was examined in 51 clinical VZV isolates sensitive to acyclovir (ACV). In addition, 16 VZV strains with clinical resistance to ACV were analyzed. None of the ACV-sensitive strains of the clades 1, 3 and 5 showed gene polymorphism of the TK. By contrast, the DNA pol gene exhibited polymorphism-related substitutions as a function of the VZV clade. The novel substitutions M286I, E824Q, R984H and H1089Y were detected in strains of clades 3 and 5. In the TK gene of 7 VZV strains with clinical ACV resistance, the novel substitutions L73I, A163stop, W225R, T256M, N334stop and the deletion of nucleotides 19-223 were found to be associated most likely with resistance. In one strain showing the substitution W225R, ACV resistance could be confirmed by the viral phenotype. In the DNA pol gene, the novel amino acid substitutions T237K and A955T could be detected, but their significance remains unclear. In conclusion, the characterization of resistance using genetic analysis of the TK and DNA pol genes has to be considered the method of choice for the determination of VZV resistance to antiviral drugs. In a considerable number of patients with clinical ACV-resistant VZV infections, resistance cannot be verified by virological methods.

Antiviral drug resistance: mechanisms and clinical implications

Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.

Viral pneumonias in immunocompromised adult hosts

Viral infections have always been considered pediatric diseases. However, viral pneumonia has become an important cause of morbidity and mortality in immuncompromised adults. Improved diagnostic techniques, such as the introduction of highly sensitive nucleic acid amplification tests, have not only allowed us to discover new viruses but also to determine the etiology of viral pneumonia in immunocompromised adult hosts. Unfortunately, only a few antiviral agents are available. Thus, early diagnosis and treatment are crucial to patient outcome. In this article, we review the most common viruses that have been implicated as etiologic agents of viral pneumonia in immunocompromised adults. We discuss the epidemiologic characteristics and clinical presentation of these viral infections and the most appropriate diagnostic approaches and therapies when available.

Antiviral drug resistance: mechanisms and clinical implications

Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.

Foscarnet salvage therapy for acyclovir-resistant varicella zoster: report of a novel thymidine kinase mutation and review of the literature

The authors describe an acyclovir-resistant varicella zoster virus infection in a pediatric patient after hematopoietic stem cell transplant, the use of foscarnet as salvage therapy, and review the literature to clarify the pediatric experience with foscarnet in this setting. A novel thymidine kinase mutation is described, along with a new phenotypic assay for characterizing acyclovir resistance in varicella zoster virus.

Tolerability of treatments for postherpetic neuralgia

Herpes zoster occurs in up to 20% of people infected with varicella-zoster virus, due to reactivation of the virus from latently infected sensory ganglia. Although pain is a typical feature of acute zoster, pain persisting for more than a month after resolution of the rash is less common and is termed postherpetic neuralgia (PHN). The pain associated with PHN is neuropathic in origin and is notoriously difficult to treat. The incidence of herpes zoster and its associated complications both increase with age, so PHN should be seen more commonly in an aging population. Vaccination with live, attenuated varicella vaccine is safe and efficacious, particularly in children. It decreases the incidence of acute varicella and subsequent herpes zoster. Aciclovir is well tolerated, with renal toxicity only at high intravenous doses. Treatment of acute varicella with aciclovir attenuates acute illness but does not prevent herpes zoster. Treatment of herpes zoster with aciclovir or its derivatives minimises symptoms and may reduce the rate of PHN. Foscarnet is an alternative for an aciclovir-resistant virus but its use is limited by renal and CNS toxicity. Corticosteroids reduce acute pain in herpes zoster but do not affect the incidence of PHN. Their use in some patients may be limited by adverse effects such as gastritis and impaired glucose tolerance. Treatment of established PHN is difficult and may require a holistic approach. Tricyclic antidepressants and gabapentin are the systemic agents with the most proven benefit, although opioids such as oxycodone and NMDA receptor antagonists such as ketamine may be useful in some people. Adverse effects from tricyclic antidepressants are common but usually mild, while gabapentin is generally well tolerated. Although effective, the relatively common adverse effects of opioids and ketamine limit their usefulness in treating PHN. Topical treatment with 5% lidocaine patch or capsaicin is of benefit in some patients and is generally well tolerated. Intrathecal methyl prednisolone may be considered for intractable pain but efficacy and safety have not been confirmed.

Actualización en el tratamiento del herpes zóster

The systemic treatment of herpes zoster shortens the healing process, and prevents or alleviates pain and other acute or chronic complications, especially when it is administered in the first 72 hours after symptoms appear. This treatment is especially indicated in patients over the age of 50 and in those who, regardless of age, have head and neck involvement, especially in herpes zoster ophthalmicus. The drugs approved in Europe for the systemic treatment of herpes zoster are aciclovir, valaciclovir, famciclovir and brivudine. Brivudine shows greater effectiveness against the varicella-zoster virus than aciclovir and its derivatives, and can be given just once a day for seven days, compared to multiple doses of the latter. As opposed to the others, brivudine is a non-nephrotoxic drug that should not be administered to immunodepressed patients or to those being treated with 5-fluorouracil. The treatment of herpes zoster to reduce pain should be combined with analgesics and neuroactive agents (amitriptyline, gabapentin, etc). While corticosteroids are of dubious efficacy in the treatment of post-herpes neuralgia, the intensity and duration of the pain can be reduced with some topical treatments (capsaicin, lidocaine patches, etc). Finally, this review discusses treatment guidelines for special locations (cranial nerves) and different subpopulations (children, pregnant women, immunodepressed patients, etc).

Antiviral therapies in children: has their time arrived?

The increase in the number and classes of antiviral agents that has occurred since the 1980s is remarkable. The rapid expansion in therapeutic options for previously untreatable illnesses challenges clinicians to gain familiarity and experience with these new drugs, especially with regard to their use in children. This article describes the clinical utilities, pharmacokinetics, and adverse effects of these new drugs to empower practitioners to use them appropriately.

[Treatment and prophylaxis of opportunistic infections in the course of HIV disease: a state of the art in 2004. Part 2: Viral, fungal and bacterial infections]

Remarkable progress has been made in antiretroviral therapeutics, as well as in the prophylaxis and treatment of opportunistic infections, since the beginning of the AIDS epidemic. The patient's life expectancy and quality of life have consequently improved, thanks to better management of opportunistic diseases. The introduction of protease inhibitors-containing regimen (i.e. highly active antiretroviral therapy or HAART), since 1996, has drastically reduced the incidence of opportunistic infections by restoring immunity. The large panel of antiretroviral drugs responsible for frequent sustained viral and immune responses has thus allowed a new definition of guidelines for the prophylaxis and treatment of opportunistic infections. A better use of prophylactic drugs should help to reduce the risk of drug-related toxicity and pharmaceutical interactions. It should also decrease the cost of HIV management and eventually increase compliance to treatment and quality of life.

In vitro selection of drug-resistant varicella-zoster virus (VZV) mutants (OKA strain): differences between acyclovir and penciclovir?

Varicella-zoster virus (VZV) mutants were isolated under the pressure of different classes of antiviral compounds: (i) drugs that depend on the viral thymidine kinase (TK) for their activation, i.e. acyclovir (ACV), brivudin (BVDU), penciclovir (PCV) and sorivudine (BVaraU); (ii) drugs that are independent of the viral TK for their activation, i.e. 2-phosphonylmethoxyethyl (PME) derivatives of adenine (PMEA, adefovir) and 2,6-diaminopurine (PMEDAP); and (iii) drugs that do not require any metabolism to inhibit the viral DNA polymerase, i.e. foscarnet (PFA). Drug-resistant virus strains were obtained by serial passage of the OKA strain in human embryonic lung (HEL) fibroblasts and the different drug-resistant mutants were subsequently evaluated for their in vitro susceptibility to a broad range of antiviral drugs. Virus strains emerging under the pressure of ACV, BVDU and BVaraU were cross-resistant to all drugs that depend on the viral TK for activation, but remained susceptible to the acyclic nucleoside phosphonates (i.e. PMEA, PMEDAP and the 3-hydroxy-2-phosphonylmethoxypropyl derivatives of adenine (HPMPA) and cytosine (HPMPC, cidofovir)) and PFA. In contrast, the virus strains selected under pressure of PCV were resistant to PCV, ACV, PMEA and PFA; but not BVDU, BVaraU, GCV, HPMPC or HPMPA. Similar patterns of drug susceptibility were noted for the virus strains selected under the pressure of PMEA or PFA, pointing to an alteration in the viral DNA polymerase as basis for the resistant phenotype selected by PCV, as well as PMEA and PFA. In contrast, the resistant phenotype selected by ACV as well as BVDU and BVaraU may be attributed primarily to mutations in the viral TK gene. Our data thus indicate that ACV and PCV select in vitro for different drug-resistant VZV phenotypes; whether this is also the situation in vivo remains to be investigated.

Current and potential therapies for the treatment of herpes-virus infections

Human herpesviruses are found worldwide and are among the most frequent causes of viral infections in immunocompetent as well as in immunocompromised patients. During the past decade and a half a better understanding of the replication and disease-causing state of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), and human cytomegalovirus (HCMV) has been achieved due in part to the development of potent antiviral compounds that target these viruses. While some of these antiviral therapies are considered safe and efficacious (acyclovir, penciclovir), some have toxicities associated with them (ganciclovir and foscarnet). In addition, the increased and prolonged use of these compounds in the clinical setting, especially for the treatment of immunocompromised patients, has led to the emergence of viral resistance against most of these drugs. While resistance is not a serious issue for immunocompetent individuals, it is a real concern for immunocompromised patients, especially those with AIDS and the ones that have undergone organ transplantation. All the currently approved treatments target the viral DNA polymerase. It is clear that new drugs that are more efficacious than the present ones, are not toxic, and target a different viral function would be of great use especially for immunocompromised patients. Here, an overview is provided of the diseases caused by the herpesviruses as well as the replication strategy of the better studied members of this family for which treatments are available. We also discuss the various drugs that have been approved for the treatment of some herpesviruses in terms of structure, mechanism of action, and development of resistance. Finally, we present a discussion of viral targets other than the DNA polymerase, for which new antiviral compounds are being considered.

Highly potent and selective inhibition of varicella-zoster virus replication by bicyclic furo[2,3-d]pyrimidine nucleoside analogues

The bicyclic furo[2,3-d]pyrimidine nucleoside analogues represent an entirely new class of fused furopyrimidine derivatives with unprecedented selectivity for varicella-zoster virus (VZV). From extensive structure-activity relationship (SAR) studies, the 6-(p-alkylphenyl)substituted furopyrimidine derivatives Cf 1742 and Cf 1743 emerged as the most potent inhibitors of VZV replication: they were found to inhibit both laboratory VZV strains and clinical VZV isolates at subnanomolar concentrations, while not being toxic to the host cells at 100,000-fold higher concentrations. Although the precise mechanism of action of these compounds remains to be elucidated, it is clear that for their antiviral activity they depend on phosphorylation by the VZV-encoded thymidine kinase. The furo[2,3-d]pyrimidine nucleoside analogues are not susceptible to degradation by human or bacterial thymidine phosphorylase, which may otherwise release the free aglycone. Also, the latter is not inhibitory to dihydropyrimidine dehydrogenase, an enzyme involved in the degradation of thymine, uracil, and the anticancer agent 5-fluorouracil. Further development of the furo[2,3-d]pyrimidine nucleoside analogues as new therapeutic modalities for the treatment of VZV infections (i.e., varicella and herpes zoster) seems highly justified.

Identification of small molecule compounds that selectively inhibit varicella-zoster virus replication

A series of nonnucleoside, N-alpha-methylbenzyl-N'-arylthiourea analogs were identified which demonstrated selective activity against varicella-zoster virus (VZV) but were inactive against other human herpesviruses, including herpes simplex virus. Representative compounds had potent activity against VZV early-passage clinical isolates and an acyclovir-resistant isolate. Resistant viruses generated against one inhibitor were also resistant to other compounds in the series, suggesting that this group of related small molecules was acting on the same virus-specific target. Sequencing of the VZV ORF54 gene from two independently derived resistant viruses revealed mutations in ORF54 compared to the parental VZV strain Ellen sequence. Recombinant VZV in which the wild-type ORF54 sequence was replaced with the ORF54 gene from either of the resistant viruses became resistant to the series of inhibitor compounds. Treatment of VZV-infected cells with the inhibitor impaired morphogenesis of capsids. Inhibitor-treated cells lacked DNA-containing dense-core capsids in the nucleus, and only incomplete virions were present on the cell surface. These data suggest that the VZV-specific thiourea inhibitor series block virus replication by interfering with the function of the ORF54 protein and/or other proteins that interact with the ORF54 protein.

Genotypic and phenotypic characterization of the thymidine kinase of ACV-resistant HSV-1 derived from an acyclovir-sensitive herpes simplex virus type 1 strain

Twenty-four strains of acyclovir (ACV)-resistant (ACV(r)) herpes simplex virus type 1 (HSV-1) were generated from the HSV-1 TAS strain by exposure to ACV, and the genotype and phenotype of the thymidine kinase (TK) from these mutants were analyzed. The TK polypeptide of the ACV(r) HSV-1 strains was examined by Western blot using an anti-HSV-1 TK rabbit serum. The sensitivity of each strain to ACV, foscarnet and cidofovir (CDV) was also determined. A single guanine (G) insertion or a single cytosine (C) deletion was detected in 12 of the 24 ACV(r) strains at the G or C homopolymer stretches within the TK gene. Genotypic analysis predicted that two thirds of the ACV(r) HSV-1 strains expressed truncated TK polypeptides, while one third expressed viral TK polypeptide with a single amino acid substitution at various sites. Western blot abnormalities in the viral TK polypeptides were identified in 21 ACV(r) strains. There was an inverse correlation between the susceptibility of the HSV-1 mutant strains to ACV and that to CDV. Nucleotide sequencing of the TK gene and Western blot analysis of the viral TK polypeptides are considered to be one of the methods for predicting virus sensitivity to ACV and CDV.

Antiviral agents: Nonantiviral drugs

The current arsenal of antiviral agents available to the practitioner is expanding rapidly, such that by the time this article goes to press, new drugs may have already been added. Although the majority of approved drugs have been developed for use in only a few viral infections (eg, HIV, herpesviruses, and papillomavirus), discoveries made in the development of these drugs may lead to antiviral agents effective against other viruses. In addition, new uses for the currently available drugs are under evaluation. This review of antiviral agents discusses the treatments available for viral infections such as herpes simplex virus, varicella zoster virus, cytomegalovirus, human papillomavirus, chronic viral hepatitis, and others.

Bone marrow transplantation in a child with Wiskott-Aldrich syndrome latently infected with acyclovir-resistant (ACV(r)) herpes simplex virus type 1: emergence of foscarnet-resistant virus originating from the ACV(r) virus

A human leukocyte antigen (HLA)-matched unrelated bone marrow transplantation (BMT) was performed in a 13-year-old patient with the congenital immunodeficiency syndrome, Wiskott-Aldrich syndrome. The patient had a history of acyclovir (ACV)-resistant (ACV(r)) herpes simplex virus type 1 (HSV-1) infections prior to BMT. After BMT, the skin lesions caused by HSV-1 relapsed on the face and genito-anal areas. Ganciclovir (GCV) therapy was initiated, but the mucocutaneous lesions worsened. An HSV-1 isolate recovered from the lesions during this episode was resistant to both ACV and GCV. The ACV(r) isolate was confirmed to have the same mutation in the viral thymidine kinase (TK) gene as that of the previously isolated ACV(r) isolates from the patient. After treatment switch to foscarnet (PFA), there was a satisfactory remission but not a complete recovery. Although the mucocutaneous lesions improved, a PFA-resistant (PFA(r)) HSV-1 was isolated 1 month after the start of PFA therapy. The PFA(r) HSV-1 isolate coded for the same mutation in the viral TK gene as the ACV(r) HSV-1 isolates. Furthermore, the PFA(r) isolate also expressed a mutated viral DNA polymerase (DNA pol) with an amino acid (Gly) substitution for Val at position 715. This is the first report on the clinical course of a BMT-associated ACV(r) HSV-1 infection that subsequently developed resistance to foscarnet as well.

Resistance of herpesviruses to antiviral drugs: clinical impacts and molecular mechanisms

Nucleoside analogues such as acyclovir and ganciclovir have been the mainstay of therapy for alphaherpesviruses (herpes simplex virus (HSV) and varicella-zoster virus (VZV)) and cytomegalovirus (CMV) infections, respectively. Drug-resistant herpesviruses are found relatively frequently in the clinic, almost exclusively among severely immunocompromised patients receiving prolonged antiviral therapy. For instance, close to 10% of patients with AIDS receiving intravenous ganciclovir for 3 months excrete a drug-resistant CMV isolate in their blood or urine and this percentage increases with cumulative drug exposure. Many studies have reported that at least some of the drug-resistant herpesviruses retain their pathogenicity and can be associated with progressive or relapsing disease. Viral mutations conferring resistance to nucleoside analogues have been found in either the drug activating/phosphorylating genes (HSV or VZV thymidine kinase, CMV UL97 kinase) and/or in conserved regions of the viral DNA polymerase. Currently available second line agents for the treatment of herpesvirus infections--the pyrophosphate analogue foscarnet and the acyclic nucleoside phosphonate derivative cidofovir--also inhibit the viral DNA polymerase but are not dependent on prior viral-specific activation. Hence, viral DNA polymerase mutations may lead to a variety of drug resistance patterns which are not totally predictable at the moment due to insufficient information on specific drug binding sites on the polymerase. Although some CMV and HSV DNA polymerase mutants have been found to replicate less efficiently in cell cultures, further research is needed to correlate viral fitness and clinical outcome.

Varicella pneumonia: another 'steroid responsive' pneumonia?

Varicella-zoster virus (VZV) pneumonitis remains an often-fatal complication of VZV infection. Antiviral agents and supportive care are widely accepted therapies. Cautious use of corticosteroids in life-threatening VZV pneumonitis may be justified. Appropriate patient selection factors are as yet unidentified and the decision to commence corticosteroid therapy in this setting is clinical.

Resistance in viruses other than HIV

The aim of this brief paper is to summarize the ways in which viruses develop resistance to currently licensed anti-viral drugs and to comment on their clinical relevance. Specific examples will be chosen to emphasize basic principles of the development of resistance and readers are referred elsewhere to a summary of resistance in HIV that follows the same principles.