Ocular herpes simplex virus infections: reduced sensitivity to acyclovir in primary disease

Ganciclovir ophthalmic gel 0.15% for the treatment of acute herpetic keratitis: background, effectiveness, tolerability, safety, and future applications

Eye disease due to herpes simplex virus (HSV) is a leading cause of ocular morbidity and the number one infectious cause of unilateral corneal blindness in the developed parts of the globe. Recurrent keratitis can result in progressive corneal scarring, thinning, and vascularization. Antiviral agents employed against HSV have primarily been nucleoside analogs. Early generation drugs included idoxuridine, iododesoxycytidine, vidarabine, and trifluridine. While effective, they tended to have low bioavailability and measurable local cellular toxicity due to their nonselective mode of action. Acyclovir 0.3% ointment is a more selective agent, and had become a first-line topical drug for acute HSV keratitis in Europe and other places outside of the US. Ganciclovir 0.15% gel is the most recently approved topical treatment for herpes keratitis. Compared to acyclovir 0.3% ointment, ganciclovir 0.15% gel has been shown to be better tolerated and no less effective in several Phase II and III trials. Additionally, topical ganciclovir does not cause adverse systemic side effects and is therapeutic at lower concentrations. Based on safety, efficacy, and tolerability, ganciclovir 0.15% gel should now be considered a front-line topical drug in the treatment of dendritic herpes simplex epithelial keratitis. Topics of future investigation regarding other potential uses for ganciclovir gel may include the prophylaxis of recurrent HSV epithelial keratitis, treatment of other forms of ocular disease caused by herpesviruses and adenovirus, and ganciclovir gel as an adjunct to antitumor therapy.

Acute Herpetic Keratitis: What is the Role for Ganciclovir Ophthalmic Gel?

Herpes simplex keratitis (HSK) is a major cause of corneal blindness in the world. Following the primary infection, the virus enters into a latent phase. Recurrent infectious or immune keratitis cause structural damage to the cornea, scarring, and may lead to blindness. Several commercially available topical and oral antiviral drugs for HSK are currently available. However, toxicity and low patient compliance hamper their use in HSK. Further, oral antiviral drugs alone are not always effective in HSK. Thus, there had been a need for safe and effective topical antiviral agents against HSK. Systemic ganciclovir has been in use for the treatment of cytomegalovirus infections. Recently, topical ganciclovir has become available for use in patients with HSK. Ganciclovir 0.15% ophthalmic gel has been shown to be both safe and effective against viruses of the herpes family. Topical ganciclovir ophthalmic gel is well tolerated and does not cause significant toxic effects on the ocular surface. Several multicenter studies have revealed the potential role of ganciclovir ophthalmic gel in the treatment and prophylaxis of epithelial HSK. In this paper, we have reviewed the pharmacology, efficacy, side effects, and the role of ganciclovir ophthalmic gel 0.15% in the treatment of acute herpetic keratitis.

Aciclovir-resistant herpes keratitis

Herpes simplex virus (HSV) keratitis is a common cause of ocular morbidity. Resistance to aciclovir is probably under recognized. We describe three cases of aciclovir-resistant herpes simplex virus keratitis treated with systemic foscarnet and present a review of the pharmacological options available to manage this condition.

Efficacy of oral antiviral prophylaxis in preventing ocular herpes simplex virus recurrences in patients with and without self-reported atopy

PURPOSE

To compare the efficacy of oral antiviral prophylactic treatment for herpes simplex virus (HSV) recurrences in patients with and without self-reported atopy.

DESIGN

Retrospective cohort comparative study.

METHODS

setting: Cornea Service, Wills Eye Hospital. study population: Patients who presented with previously diagnosed ocular HSV between March 2003 and March 2004. From 244 patients invited, 54 patients (58 eyes) were included. One hundred and ninety patients were excluded according to exclusion criteria: no active episode during follow-up, immunosuppression, less than one year of follow-up, or previous history of penetrating keratoplasty. The Questionnaire regarding history of atopic disease, considers: presence of allergic rhinitis, asthma or atopic dermatitis, and chart review of ocular history. main outcome measures: Incidence of all types of HSV recurrences with and without antiviral prophylaxis within each group and between groups. HSV episodes were classified into infectious, inflammatory, and mixed for analysis.

RESULTS

Atopic/nonatopic (P value): mean follow-up without prophylaxis 8.1 (+/- 8.2)/7.3 years (+/- 8.6) (P = .71); mean follow-up with prophylaxis 2.9 (+/- 2.3)/2.6 years (+/- 2.2) (P = .51); the effect of prophylaxis significantly reduced the all recurrences in both groups except in the inflammatory recurrences in the atopic group and in the mixed recurrences in both groups. Prophylaxis decreased infectious episodes by 44% in nonatopic and 76% in atopics and decreased inflammatory manifestations by 69% in the nonatopic group and 8% in the atopic group.

CONCLUSION

Antiviral prophylaxis for HSV recurrences was more effective in reducing infections in atopics and less effective in reducing inflammatory episodes in atopics versus nonatopics.

Acyclovir-resistant bilateral keratitis associated with mutations in the HSV-1 thymidine kinase gene

PURPOSE

To evaluate the contribution of molecular methods for the diagnosis of an acyclovir-resistant HSV-1 bilateral keratitis in an AIDS patient and to report a new point mutation in the nucleotide sequence of the thymidine kinase (tk) gene involved.

METHODS

A 31 year old HIV-positive female presented with severe, active, bilateral and sight-threatening keratitis of 6 months duration, which was treated unsuccessfully with acyclovir. After corneal biopsy, samples were analysed by standard virological procedures, in situ hybridization, and PCR. The tk gene was cloned and subsequently sequenced.

RESULTS

Conventional virological methods remained inconclusive. However, in situ hybridization and PCR rapidly confirmed the diagnosis of HSV-1 keratitis. The tk gene sequence revealed the presence of five variations previously described in two reference strains, but also a new point mutation at nucleotide position 431 which leads to an amino-acid change at position 144 that supported the hypothesis of a putatively altered functional form of the enzyme. Intravenous foscarnet treatment in an induction regimen was effective and cicatrization occurred within 3 weeks.

CONCLUSIONS

PCR and in situ hybridization are effective and powerful techniques when other virological procedures are non-contributive, particularly in immunocompromised patients previously treated with antiviral drugs. The new point mutation identified in the tk gene may be associated with resistance to acyclovir.

Acyclovir resistance in herpes simplex virus isolates from keratitis cases: an analysis from a developing country

Seven herpes simplex type-1 (HSV-1) isolates from herpes simplex keratitis (HSK) cases clinically resistant to acyclovir (ACV) were analyzed for the mechanism of ACV resistance in them. The purpose of the study was to focus the attention of ophthalmologists on the frequency of occurrence of ACV resistance in HSK and to characterize such a phenomenon. We employed in-vitro plaque reduction assay, thymidine kinase assay, polymerase chain reaction, single-strand confirmation polymorphism analysis and sequencing to detect any mutation(s) in thymidine kinase gene in this analytical study. Four of the seven HSV-1 isolates proved ACV resistant by plaque reduction assay and three of them showed reduced thymidine kinase activity. Altered mobility pattern indicative of mutation within 335 base pair PCR product bracketing the suggested homopolymer mutational hotspot (7 Guanosine) was detected in 2 of these 3 isolates. DNA sequencing showed a deletion at nucleotide position 336 from the tk gene transcription start in both the isolates. This mutation has generated the first TGA stop codon 27 nucleotides downstream in the tk open reading frame. Our study also suggests the need of clinical/molecular surveillance of ACV resistance in HSV types in a given geographic location for better management of HSV infections.

Clinical characteristics of acyclovir-resistant herpetic keratitis and experimental studies of isolates

BACKGROUND

We treated two patients with dendritic keratitis that did not respond to acyclovir (ACV) ointment therapy. Their systemic immune status was normal: however, one patient had a long history of atopic disease and the other had previously undergone topical corticosteroid treatment. HSV-1 was isolated from the patients and inoculated into animals to investigate its viral pathogenicity and latent infection.

METHODS

HSV-1 isolates from the patients were tested for drug sensitivity to acyclovir, ganciclovir, idoxuridine, trifluridine, foscarnet and interferon-beta in vitro. In in vivo studies, bilateral corneas of two New Zealand white rabbits and 10 BALB/c mice in each of four groups were infected by the respective viral isolates. The extent of corneal epithelial and/or stromal lesions produced by the viruses was evaluated. The trigeminal ganglial tissues of the mice were examined for viral latent infection by co-culture with Vero cells.

RESULTS

Herpetic keratitis in both patients was characterized by prolonged clinical course, succeeded by various types of corneal lesions and ocular complications. In in vitro studies, the two HSV-1 isolates demonstrated cross-resistance to ACV, ganciclovir and/or idoxuridine. Both strains demonstrated weakly virulent corneal epithelial and/or stromal lesions in rabbits and mice. One isolate displayed delayed advent but prolonged course of epithelial lesions in rabbits. The latent infection incidences of the isolates in mice trigeminal ganglia were 6.25% (1/16) and 0% (0/18) respectively.

CONCLUSION

Topical immune depression may induce ACV-resistant HSV-1 infection in the cornea, with a prolonged course in association with ocular complications. The prolonged infectious course of the viral isolates in the animal study partially supported the clinical demonstrations in the patient. The existence of latent infection by one ACV-resistant HSV-1 in its animals may indicate the possibility of its recurrence. Trifluridine may be an alternative choice for treating corneal epithelial lesions caused by ACV-resistant HSV-1.

Aciclovir. A reappraisal of its antiviral activity, pharmacokinetic properties and therapeutic efficacy

Aciclovir (acyclovir) is a nucleoside analogue with antiviral activity in vitro against the herpes simplex viruses (HSV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV) and human herpesvirus 6 (HHV-6). Topical, oral or intravenous aciclovir is well established in the treatment of ophthalmic, mucocutaneous and other HSV infections, with intravenous aciclovir the accepted treatment of choice in herpes simplex encephalitis. The efficacy of aciclovir is increased with early (preferably during the prodromal period) initiation of treatment but, despite significant clinical benefit, viral latency is not eradicated, and pretreatment frequencies of recurrence usually continue after episodic acute treatment is completed. Intravenous administration has also shown benefit in the treatment of severe complications of HSV infection in pregnancy, and neonatal HSV infections. Recurrence of HSV has been completely prevented or significantly reduced during suppressive therapy with oral aciclovir in immunocompetent patients. Use of oral aciclovir is effective but controversial in the treatment of otherwise healthy individuals with varicella (chickenpox), and in some countries it has been recommended for use only in cases which may be potentially severe. The development of rash and pain associated with herpes zoster (shingles) is attenuated with oral or intravenous aciclovir therapy, ocular involvement is prevented, and post-herpetic neuralgia appears to be decreased. Similarly, in a few patients with zoster ophthalmicus, oral aciclovir has reduced the frequency and severity of long term ocular complications and post-herpetic neuralgia, and herpes zoster oticus is improved with intravenous aciclovir. Oral aciclovir has prevented recurrence of HSV genital or orofacial infections during suppressive therapy in > 70% of immunocompetent patients in most clinical trials. Suppression of latent HSV, VZV and CMV infections has been achieved in many immunocompromised patients receiving the oral or intravenous formulations. Aciclovir also appears to offer partial protection from invasive CMV disease in CMV-seropositive bone marrow transplant recipients. The few comparative trials published have shown aciclovir to be at least as effective as other investigated antivirals in the treatment of HSV infections in immunocompetent patients, and more effective than inosine pranobex in the prophylaxis of genital herpes. Similarly, in isolated clinical trials, oral aciclovir appears as effective as topical idoxuridine and oral brivudine in some parameters in immunocompetent patients with VZV infections, and the intravenous formulation appears at least as effective as oral brivudine and intravenous vidarabine in treating these infections in immunocompromised patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Acyclovir-resistant herpes simplex virus keratouveitis after penetrating keratoplasty

PURPOSE

A case of acyclovir-resistant herpes simplex virus keratouveitis after penetrating keratoplasty is reported.

METHODS

Resistance to acyclovir was evident clinically and was confirmed by in vitro susceptibility testing. The susceptibility of the herpes simplex isolates to acyclovir and foscarnet was determined by a dye uptake assay that measured cytopathic effect, and thymidine kinase activity was measured by a plaque autoradiography technique.

RESULTS

The viral isolate from postoperative day 22 was susceptible to acyclovir and foscarnet, and showed normal thymidine kinase activity. Isolates from postoperative days 29 and 32 (coinciding with deterioration in clinical appearance) were resistant to acyclovir, susceptible to foscarnet, and deficient in thymidine kinase activity.

CONCLUSION

Practitioners should be aware of the potential for the emergence of resistance in this setting; prophylaxis and rational alternate therapies are discussed.

Systemic antiviral drugs used in ophthalmology

Over the past two decades, the recognition of viral enzymes and proteins that can serve as molecular targets of drugs has revolutionized the treatment of viral infections. Beginning with acyclovir, a number of systemically administered agents which are both relatively safe and effective for the treatment of herpetic infections and human immunodeficiency virus (HIV) infections have become widely available. Because of increased numbers of herpes virus infections, as well as the rising epidemic of HIV infections, the ophthalmologist is, more likely than ever before to be involved in the treatment of severe and frequent ocular infections caused by herpes viruses. In addition, the acute retinal necrosis (ARN) syndrome has been demonstrated to be caused by herpes viruses and a once rare retinal infection caused by cytomegalovirus is common in patients with the acquired immunodeficiency syndrome (AIDS). In this article, four systemic antiviral drugs (Vidarabine, Acyclovir, Ganciclovir, and Foscarnet) that have demonstrated usefulness in the treatment of ophthalmic disease are reviewed in detail with regard to their mechanisms, applications, effectiveness, and side effects.

Emergence of cross-resistant herpes simplex virus following topical drug therapy in rabbit keratitis

The acquisition of drug resistance in vivo was investigated by 7 serial passages (from P0 to P7) of herpes simplex virus (HSV-1) in rabbit cornea treated with either IUdR (idoxuridine), IDC (idoxycytidine), ACV (acyclovir), TFT (trifluridine), or Ara A (adenine arabinoside). Therapeutic failure was acquired gradually: at P3 for IUdR, at P4 for ACV and at P5 for TFT. At P7, viral thymidine kinase (TK) activity was reduced to 5.6% of the parental strain for IUdR, to 7.5% for ACV and to 4.6% for TFT treatment. No signs of clinical unresponsiveness occurred with IDC or Ara A. The in vitro determination of antiviral drug sensitivity performed by the dye-uptake assay on HSV isolates at each passage showed a correlation between the increase in the 50% effective dose (ED50) and the increase of ulcer area grade at each passage under antiviral drug (p less than 0.1). Both IUdR- and TFT-resistant HSV1 developed cross-resistances to TK dependent drugs. However ACV-resistant HSV1 did not show cross-resistance to other antiviral TK dependent drugs. The acquisition of the cross-resistances is discussed, and the practical implications in case of therapeutic failures are suggested.