2'-Nor-2'-deoxyguanosine is an effective therapeutic agent for treatment of experimental herpes keratitis

Efficacy and safety of topical ganciclovir in the management of cytomegalovirus (CMV)-related anterior uveitis

BACKGROUND

The aim of this study was to evaluate the efficacy and safety of topical ganciclovir 0.15 % gel in the management of patients with cytomegalovirus (CMV) anterior uveitis.

RESULTS

This was a retrospective cohort study of the disease course of 31 patients (33 eyes) with aqueous polymerase chain reaction (PCR) positive for CMV. Data from a total of 160 episodes of anterior uveitis flare for 20 years, dating from December 1992 to December 2012, was collected. All patients were treated with concomitant topical anti-inflammatory medication. The disease course of each eye was analysed before and after the use of topical ganciclovir 0.15 %. The mean age at initial presentation of anterior uveitis was 57.5 ± 12.6 years. Twenty-eight (90.3 %) patients were Chinese. Patients on topical ganciclovir gel had a statistically significant fewer episodes of uveitis flare per person year (median -0.88 episodes/person years, p = 0.029). The time-to-quiescence was not significantly affected by topical ganciclovir use (median -1.25 days, p = 0.610). In the survival analysis using the Cox regression model, the use of topical ganciclovir was associated with a lower risk of recurrence, but this was not statistically significant (hazard ratio = 0.857, 95 % CI 0.543-1.36, p = 0.511). The overall median time-to-recurrence was 290 days (95 % CI 113 to 274 days) and 164 days (125 to 404 days) (p = 0.492), with and without topical ganciclovir, respectively.

CONCLUSIONS

Topical ganciclovir may be beneficial in reducing the frequency of recurrence in patients with CMV anterior uveitis, but it was not statistically associated with prolonging the time-to-recurrence. The time-to-quiescence was also not significantly affected by topical ganciclovir. Prospective studies with a larger number of patients would be required to verify our findings.

Topical ganciclovir in the treatment of acute herpetic keratitis

Herpetic keratitis is caused by herpes simplex virus (HSV) and is a common cause of corneal blindness. Following a primary ocular herpetic infection, latency of the virus occurs, followed by subsequent recurrences of herpetic keratitis. Such recurrences may lead to structural damage of the cornea. Recurrent herpetic keratitis is a common indication for corneal transplantation. Recurrences of herpetic keratitis in the corneal graft may lead to corneal graft rejection. Several antiviral agents for HSV are available, including the thymidine analogs. Prolonged use of thymidine analogs may lead to toxicity of the ocular surface, including epithelial keratitis, corneal ulcers, follicular conjunctivitis, and punctal occlusions. Availability of topical antiviral agents that are safe and effective in the treatment and prophylaxis of herpetic keratitis is highly desirable. Ganciclovir is a potent inhibitor of members of the herpes virus family. The drug has been used systemically for the treatment of cytomegalovirus (CMV) retinitis. Its hematologic toxicity secondary to systemic administration led to its limited use in herpetic infections. On the other hand, topical ganciclovir has been shown to be as safe and effective as acyclovir in the treatment of herpetic epithelial keratitis. Furthermore, topical ganciclovir can reach therapeutic levels in the cornea and aqueous humor following topical application. Several clinical trials have shown that topical ganciclovir 0.15% ophthalmic gel is safe and effective in the treatment and prophylaxis of herpetic epithelial disease. Long-term use of ganciclovir ophthalmic gel in patients with penetrating keratoplasty following herpetic keratitis has prevented recurrences of the disease. Topical ganciclovir ophthalmic gel is well tolerated, does not cause toxic effects on the ocular surface, and does not cause hematologic abnormalities. Clinical studies have underscored the potential role of ganciclovir ophthalmic gel in the treatment and prophylaxis of herpetic epithelial keratitis. Future randomized, controlled, multicenter, prospective clinical trials are needed to assess the long-term safety and efficacy of topical ganciclovir in the treatment and prevention of herpetic keratitis and uveitis.

Pharmacologic strategies in the prevention and treatment of corneal transplant rejection

Corneal transplantation remains one of the most successful organ transplantation procedures in humans. The unique structure of the cornea, with its absence of blood vessels and corneal lymphatic, allows the survival of corneal allograft. Recent advances in sutures, storage media, microsurgical instrumentation, and new pharmacological strategies have greatly improved the success of corneal transplantation and the prevention of corneal allograft rejection. Our strategies in the management and prevention of corneal graft rejection can modify and improve the survival of corneal allografts. Preoperative evaluation, understanding the risk factors, and management of ocular surface disorders may greatly improve the survival of the corneal transplant. Early recognition of corneal allograft rejection and aggressive treatment may improve the survival of the corneal graft. Furthermore, patients who undergo corneal transplantation should be maintained under close ophthalmic surveillance and patients should be informed to report immediately whenever symptoms of corneal graft rejection occur. The mainstay of therapy is topical corticosteroids. In severe cases, periocular, intravenous, and oral corticosteroids therapy can be rendered. New therapeutic modalities such as cyclosporine, tacrolimus, daclizumab, mycophenolate mofetil, leflunomide, rapamycin, and others may prove to be of help in the prevention and treatment of corneal graft rejection. Early recognition of corneal graft rejection and prompt treatment are mandatory for the successful survival of the corneal allograft.

Ganciclovir. A review of its antiviral activity, pharmacokinetic properties and therapeutic efficacy in cytomegalovirus infections

Ganciclovir is a nucleoside analogue with antiviral activity in vitro against members of the herpes group and some other DNA viruses. It has demonstrated efficacy against human cytomegalovirus infections and should be considered a first-line therapy in the treatment of life- or sight-threatening cytomegalovirus infection in immunocompromised patients. Clinical efficacy varies with the underlying aetiology of immunocompromise and the site of disease, and prompt diagnosis and early treatment initiation appear to improve the response. In patients with cytomegalovirus pneumonia, particularly bone marrow transplant recipients, concomitant administration of cytomegalovirus immune globulin may significantly improve clinical outcome. Maintenance therapy to prevent recurrence is usually required by bone marrow transplant recipients until the recovery of adequate immune function, whereas AIDS patients may require indefinite ganciclovir maintenance therapy to prevent disease progression, as ganciclovir (like other antivirals) does not eradicate latent viral infection. Haematological effects occur relatively frequently during ganciclovir administration but are usually reversible. Ganciclovir has not been directly compared with other antiviral drugs because of the absence until recently of other effective treatments. However, comparative studies with foscarnet, particularly in cytomegalovirus retinitis, will be of considerable interest. Thus, ganciclovir represents a major advance in the therapy of severe cytomegalovirus infections in immunocompromised patients. Comparative studies, and investigation of ways of reducing toxicity (intravitreal administration; concomitant use of stimulants of haematopoiesis; use in conjunction with other antivirals with differing mechanisms of action), may further expand its eventual role.

Significance of resistance of herpes simplex virus to acyclovir

The genome of herpes simplex virus codes for several enzymes, including viral thymidine kinase and viral deoxyribonucleic acid (DNA) polymerase. When viral resistance develops, it does so by changes in these two enzymes. Three possible mechanisms of viral resistance to acyclovir include (1) selection of viral mutants that make little or no thymidine kinase and do not phosphorylate acyclovir adequately, (2) selection of mutants that can phosphorylate thymidine but cannot phosphorylate acyclovir (i.e., these viruses have thymidine kinases with altered substrate specificity), and (3) selection of viruses that have altered DNA polymerases that replicate viral DNA in the presence of acyclovir triphosphate. Thymidine kinase-deficient virus has been isolated from clinical isolates frequently, but few strains appear to be virulent for animals or humans and only a few seem to have caused clinical disease. Viruses with altered substrate specificity have been reported but viruses with an altered DNA polymerase have not occurred in clinical practice. Antiviral drugs should be used only when necessary to minimize the appearance of resistant strains of virus.