Acyclovir--resistant Herpes Simplex Virus Keratouveitis after Penetrating Keratoplasty Peter L. Sonkin, MD, 1 Keith H. Baratz, MD, 1 Richard Frothingham, MD, 2 L. Michael Cobo, MD1 Purpose: A case of acyclovir-resistant herpes simplex virus keratouveitis after pen etrating 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. Resuns: 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. Ophthalmology 1992;99: 1805-1808
Acyclovir has had a dramatic impact on the treatment of herpes simplex virus (HSV) infections at all sites, including ocular. Resistance to acyclovir has been an increasing problem in severely immunocompromised patients, es pecially those with acquired immune deficiency syndrome (AIDS) 1•2 and after bone marrow transplantation, 3 and usually occurs in the setting of prolonged or multiple courses of acyclovir therapy. 3-6 Although failure to heal in clinical herpetic keratitis is a relatively common prob lem (with persistence of infection despite apparently ad equate antiviral treatment), 7 surveys have failed to show a significant rate of clinical isolates with in vitro resis tance.7.8 We report on a patient in whom the emergence ofin vitro resistance to acyclovir was associated with clin ical resistance and eventual failure of a corneal graft.
Originally received: May 22, 1992. Revision accepted: July 29, 1992. 1 Department of Ophthalmology, Duke University Medical Center, Durham. 2 Department of Internal Medicine, Duke University Medical Center, Durham. Reprint requests to Keith H. Baratz, MD, Department ofOphthalmology, Mayo Clinic, Rochester, MN 55905.
Case Report The patient is a 62-year-old, HIV-negative man with a history of well-controlled bilateral glaucoma, recurrent bilateral HSV keratouveitis, and three corneal transplantation procedures in the right eye complicated by allograft rejection, recurrent herpetic keratouveitis, and graft failure. The patient underwent an uncomplicated fourth penetrating keratoplasty in the right eye. Immediately after surgery, a drug regimen was begun, which consisted of topical prednisolone ac etate I% every 2 hours while awake, cyclosporine A 2% ointment twice daily, dexamethasone 0.05% ointment at bedtime, cyclo pentolate I% twice daily, betaxolol 0.5% twice daily, and gen tamicin 0.3% twice daily. On postoperative day 4, the cyclopen tolate and gentamicin were stopped, and the prednisolone was decreased to six times daily. Antiviral medications were not used in the immediate postoperative period. On postoperative day 14, the patient returned for routine follow-up and was found to have new keratic precipitates, an endothelial rejection line, and a central graft thickness of 0.70 mm compared with 0.66 mm I week previously. Visual acuity was 20/200, improving with pinhole to 20/80. Graft rejection was suspected, and 125 mg of methylprednisolone was admin istered intravenously. High-dose topical steroids and oral pred nisone were prescribed. Because of previous hypersensitivity to topical antiviral agents, oral acyclovir was prescribed for antiviral prophylaxis. The patient, however, did not have the prescription for acyclovir filled.
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On postoperative day 22, the patient returned with geographic epithelial defects and stromal infiltrates at the superior and in ferior graft-host junctions. Visual acuity was counting fingers, improving with pinhole to 20/400. Pachymetry was 0.72 mm centrally. The patient was hospitalized and treated with 600 mg of intravenous acyclovir every 8 hours, prednisolone acetate I% every 1 hour while awake, and 125 mg of intravenous methyl prednisolone every 6 hours. The cyclosporine A ointment was continued. Corneal culture on postoperative day 22 was positive for HSV. Initially, the clinical appearance improved. Topical steroids were decreased, and the intravenous steroid dosage was changed to 60 mg of oral prednisone every day. The acyclovir was switched to 400 mg administered orally, five times daily, on postoperative day 27. On postoperative day 28, a new epithelial defect and infiltrate developed. Culture on postoperative day 29 was again positive for HSV. Acyclovir, 600 mg intravenously every 8 hours, was resumed, and over the next several days extensive stromal ne crosis developed, which was accompanied by a Seidel-positive wound dehiscence. The epithelial defect enlarged to encompass the entire cornea and a portion of the adjacent perilimbal con junctiva despite the use of topical trifluridine I% and then idox uridine 0.5% ointment. The wound leak resolved spontaneously. Topical antiviral agents were discontinued on postoperative day 31. Repeat corneal culture on postoperative day 32 was again positive for HSV. Cyclosporine A ointment was discon tinued at this time, and topical antivirals were not restarted. Ganciclovir 300 mg intravenously every 12 hours was added to the regimen on postoperative day 36 without improvement over the next week. By postoperative day 43, the inflammation began to decrease, and the epithelial disease resolved. By postoperative day 57, complete re-epithelialization had occurred. The visual acuity in the right eye returned to 20/200 uncorrected. The pa tient was discharged on oral acyclovir 600 mg three times daily, oral prednisone 15 mg daily, and betaxolol 0.5% in both eyes twice daily. On later follow-up, the graft was considered to be failed on the basis of stromal thickening and haze. Relevant laboratory data during admission included a neg ative HIV ELISA and a normal lymphocyte subset analysis of T4 = 38%, T8 = 23% (ratio = 1.65).
Laboratory Methods The susceptibility of the HSV isolates to acyclovir and foscarnet was determined by a dye uptake assay that mea sures quantitative cytopathic effect. 9 Briefly, vero cells were challenged with the viral isolates, and the cytopathic effect at 72 hours was measured by the uptake of neutral red dye. The ID 50 was the concentration of acyclovir or foscarnet that resulted in a 50% reduction in dye uptake
compared with cell controls ( 100%) and virus controls (0%). An ID 5o > 3.0 ~g/ml of acyclovir or ID 50 > 200 ~g/ml of foscarnet was considered indicative of resistance. Vero cells infected with the HSV isolates were assayed for thymidine kinase activity by using a plaque autora diography technique as described by Martin et al. 10
Laboratory Results The initial corneal isolate obtained from the patient before the institution of intravenous therapy was susceptible to acyclovir and positive for thymidine kinase activity (Table I). Isolates obtained later in the patient's hospital course were resistant to acyclovir and deficient in thymidine ki nase. All viral isolates were susceptible to foscarnet.
Discussion This case demonstrates the emergence of acyclovir-resis tant HSV keratouveitis while receiving therapy, associated with clinical failure of a corneal graft. This patient was not severely immunocompromised, as has been the case in most patients reported with acyclovir-resistant HSV infections. However, he had undergone a corneal graft procedure and was receiving oral steroids, topical steroids, and topical cyclosporine. These factors may have con tributed to the development of resistance. This patient resembles previously described patients with acyclovir resistant non ocular HSV in that he has a history of pro longed HSV infection, multiple exposures to acyclovir, and use of steroids. This case is unique in that the patient did not have AIDS, was not severely immunocompro mised, and had an ocular site of infection. Review of the literature showed only two previous reports ofocular HSV infection that document in vitro resistance to acyclovir. In one study, reduced sensitivity to acyclovir was identified in 3 of 40 isolates from patients with primary infections acquired in the community and without a previous history of treatment with acyclovir; no clinical resistance was noted. 11 The second report is of a 15-year-old girl with AIDS and herpetic keratitis, who did not respond to high dose oral acyclovir, topical trifluridine, topical idoxuri dine, and topical vidarabine, but eventually improved with topical alpha-interferon; in vitro resistance to acyclovir was identified. 12
Table 1. Antiviral Susceptibility and Thymidine Kinase Activity Acyclovir Isolate
IDso (~tg/ml) ± SE
POD22 POD29 POD32
0.27 ± 0.18 (S) 9.4 ± 6.51 (R) 15.2 ± 7.4 (R)
TK = thymidine kinase; S = susceptible; R = resistant.
1806
Foscarnet IDso
(~tgfml)
± SE
56± 5.8 (S) 37 ± 11 (S) 20 ± 40 (S)
TK Activity Positive Deficient Deficient
Sonkin et al · Acyclovir-resistant HSV Keratouveitis after PK Acyclovir is phosphorylated by HSV-specific thymidine kinase, and is then further phosphorylated to acyclovir triphosphate by host cell kinases. 13- 15 The triphosphate is the active form of acyclovir that inhibits the viral DNA polymerase and is incorporated into the viral DNA chain. 16- 18 Most clinical isolates ofacyclovir-resistant HSV have been deficient in thymidine kinase (TK-). 1·19·20 TK strains exhibit decreased virulence in animal mod els,21-23 and early reports suggested that TK- mutants have reduced clinical virulence. 3 However, recent reports have noted severe mucocutaneous disease due to TK strains in patients with AIDS or after bone marrow trans plantation.1·19 Our patient had a TK- acyclovir-resistant strain, which caused severe keratouveitis and contributed to graft failure. Resistant strains of HSV with normal in duction of thymidine kinase (TK +) also have been iso lated. These TK+ mutants either have an altered DNA polymerase, which is not susceptible to acyclovir-tri phosphate, 24 or a thymidine kinase enzyme with altered substrate specificities (i.e., less able to phosphorylate acy clovir).25,26 Prophylactic acyclovir for herpes simplex virus kera touveitis or corneal grafting has received relatively little attention in the literature. Prophylaxis for nonocular HSV has been advocated for patients considered to be at high risk, such as seropositive bone marrow transplant pa tientsY Resistance, however, can emerge on exposure to acyclovir and has occurred with prophylaxis in other set tings.19 Low-dose prophylactic acyclovir has actually been shown to select for resistant virus in animal studies. 21 En glund et al 19 reported that low-dose therapy during a virus free period antedated the isolation of resistant virus in one patient. Furthermore, long-term oral or low-dose suppressive therapy in symptomatic patients may also potentiate selection of resistant strains. When using pro phylactic acyclovir after penetrating keratoplasty, the emergence or persistence of active infection should alert the ophthalmologist that a resistant infection may be present. Definite therapeutic recommendations for ocular dis ease due to acyclovir-resistant HSV cannot be made be cause of the limited clinical experience. In addition to topical antiviral agents (which remain an integral part of clinical management), there are several possible alternate therapies available. Foscarnet is becoming a drug ofchoice for acyclovir-resistant mucocutaneous disease in AIDS patients. Controlled trials have shown foscarnet to be more effective and less toxic than vidarabine in this setting_28-30 Foscarnet is generally well-tolerated in these studies, al though renal and other toxicities are observed in some patients. Foscarnet is a pyrophosphate analog that inhibits HSV DNA polymerase without activation by viral thy midine kinase, 1 and it remains effective against the more common TK- resistant mutants. 1·29 High-dose, contin uous, intravenous acyclovir also has been effective in treating mucocutaneous disease due to resistant HSV. 2·19 However, high-dose intermittent intravenous acyclovir was not effective in our patient. Discontinuation of acy clovir therapy also has been used therapeutically in non ocular infections because it can result in the return of
sensitive virus, 19 but this approach may not be practical in ocular settings. Ganciclovir is structurally similar to acyclovir and also requires phosphorylation by HSV thy midine kinase to become activated. It is not a rational choice for the treatment of acyclovir-resistant HSV, and it has not been effective when used. 1 Patients receiving ganciclovir for acyclovir-resistant HSV do not improve clinically, nor do these viral isolates show in vitro suscep tibility to ganciclovir. 1 Our patient seemed to improve after onset of ganciclovir therapy. In vitro susceptibility and thymidine kinase assay results were not immediately available to aid in therapeutic decisions. However, given the mechanism of action of the drug and the fact that acyclovir-resistant HSV infections may undergo sponta neous healing, 31 it is unlikely that ganciclovir helped our patient. Although the role of ganciclovir in the course of this patient's disease is unclear, this drug should not be a primary alternative. Lastly, topical alpha-interferon has been used successfully to treat acyclovir-resistant HSV keratouveitis in a patient with AIDS. 12 Ophthalmologists should be aware of the potential for acyclovir-resistant HSV infections after penetrating ker atoplasty, especially in those patients with previous HSV infections or exposure to acyclovir. Rapid procedures for the determination of HSV acyclovir susceptibility are re ported and should be made more widely available. 19 Ra tional alternate therapies are available for acyclovir-resis tant HSV. Acknowledgment. The authors thank Edgar L. Hill, PhD,
Department of Virology, Burroughs Wellcome Co, Research Triangle Park, NC, for in vitro drug susceptibility testing and thymidine kinase assays.
References 1. Erlich KS, Mills J, Chatis P, et al. Acyclovir-resistant herpes simplex virus infections in patients with the acquired immu nodeficiency syndrome. N Eng) J Med 1989;320:293-6. 2. Engel JP, Englund JA, Aetcher CV, Hill EL. Treatment of resistant herpes simplex virus with continuous-infusion acyclovir. JAMA 1990;263: 1662-4. 3. Wade JC, McLaren C, Meyers JD. Frequency and signifi cance of acyclovir-resistant herpes simplex virus isolated from marrow transplant patients receiving multiple courses of treatment with acyclovir. J Infect Dis 1983;148: 1077 82. 4. Crumpacker CS, Schnipper LE, Marlowe SI, et al. Resistance to antiviral drugs ofherpes simplex virus isolated from a patient treated with acyclovir. N Eng) J Med 1982;306:343-6. 5. Bums WH, Saral R, Santos GW, et al. Isolation and char acterisation of resistant herpes simplex virus after acyclovir therapy. Lancet 1982;1:421-3. 6. Sibrack CD, Gutman LT, Wilfert CM, et al. Pathogenicity of acyclovir-resistant herpes simplex virus type 1 from an immunodeficient child. J Infect Dis 1982;146:673-82. 7. Menage MJ, de Clercq E, van Lierde A, et al. Antiviral drug sensitivity in ocular herpes simplex virus infection. Br J Ophthalmol 1990;74:532-5. 8. Mori Y, Inoue Y, Shimomura Y, Manabe R. In vitro sen sitivity to antiviral agents of herpes simplex viruses isolated from patients with herpetic keratitis. Nippon Ganka Gakkai Zasshi 1990;94:484-7.
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9. McLaren C, Ellis MN, Hunter GA. A colorimetric assay for the measurement ofthe sensitivity of herpes simplex viruses to antiviral agents. Antiviral Res 1983;3:223-34. 10. Martin JL, Ellis MN, Keller PM, et al. Plaque autoradiog raphy assay for the detection and quantitation ofthymidine kinase-deficient and thymidine kinase-altered mutants of herpes simplex virus in clinical isolates. Antimicrob Agents Chemother 1985;28:181-7. 11. Charles SJ, Gray JJ. Ocular herpes simplex virus infection: reduced sensitivity to acyclovir in primary disease. Br J Ophthalmol 1990;74:286-8. 12. McLeish W, Pflugfelder SC, Crouse C, et al. Interferon treatment of herpetic keratitis in a patient with acquired immunodeficiency syndrome [letter]. Am J Ophthalmol 1990; 109:93-5. 13. O'Brien JJ, Campoli-Richards DM. Acyclovir. An updated review of its antiviral activity, pharmacokinetic properties and therapeutic efficacy. Drugs 1989;37:233-309. 14. Fyfe AJ, Keller PM, Furman PA, et al. Thymidine kinase from herpes simplex virus phosphorylates the new antiviral compound, 9-(2-hydroxyethoxymethyl)guanine. J Bioi Chern 1978;253:8721-7. 15. Miller WH, Miller RL. Phosphorylation of acyclovir (acy cloguanosine) monophosphate by GMP kinase. J Bioi Chern 1980;255:7204-7. 16. Elion GB, Furman PA, Fyfe JA, et al. Selectivity of action of an antiherpetic agent, 9-(2-hydroxyethoxymeth yl)guanine. Proc Natl Acad Sci USA 1977;74:5716-20. 17. Furman PA, St. Clair MH, Fyfe JA, et al.Inhibition of herpes simplex virus-induced DNA polymerase activity and viral DNA replication by 9-(2-hydroxyethoxymethyl)guanine and its triphosphate. J Virol 1979;32:72-7. 18. Furman PA, St. Clair MH, Spector T. Acyclovir triphosphate is a suicide inactivator of the herpes simplex virus DNA polymerase. J Bioi Chern 1984;259:9575-9. 19. Englund JA, Zimmerman ME, Swierkosz EM, et al. Herpes simplex virus resistant to acyclovir. A study in a tertiary care center. Ann Intern Med 1990;112:416-22. 20. Ellis MN, Waters R, Hill EL, et al. Orofacial infection of athymic mice with defined mixtures of acyclovir-susceptible
1808
21. 22. 23. 24.
25. 26. 27. 28.
29.
30.
31.
and acyclovir-resistant herpes simplex virus type 1. Anti microb Agents Chemother 1989;33:304-10. Field HJ. Development ofclinical resistance to acyclovir in herpes simplex virus-infected mice receiving oral therapy. Antimicrob Agents Chemother 1982;21 :744-52. Field HJ, Darby G. Pathogenicity in mice ofstrains of herpes simplex virus which are resistant to acyclovir in vitro and in vivo. Antimicrob Agents Chemother 1980; 17:209-16. Tenser RB, Miller RL, Rapp F. Trigeminal ganglion infec tion by thymidine kinase-negative mutants ofherpes simplex virus. Science 1979;205:915-7. Furman PA, Coen DM, St. Clair MH, Schaffer PA. Acy clovir-resistant mutants of herpes simplex virus type 1 ex press altered DNA polymerase or reduced acyclovir phos phorylating activities. J Virol 1981 ;40:936-41. Darby G, Field HJ, Salisbury SA. Altered substrate specificity of herpes simplex virus thymidine kinase confers acyclovir resistance. Nature 1981 ;289:81-3. Larder BA, Darby G. Properties of a novel thymidine kinase induced by an acyclovir-resistant herpes simplex virus type I mutant. J Virol 1982;42:649-58. Am binder RF, Bums WH, Lietman PS, Saral R. Prophy laxis: a strategy to minimise antiviral resistance. Lancet 1984;1:1154-5. Safrin S, Assaykeen T, Follansbee S, Mills J. Foscamet ther apy for acyclovir-resistant mucocutaneous herpes simplex virus infection in 26 AIDS patients: preliminary data. J In fect Dis 1990; 161: 1078-84. Safrin S, Crumpacker C, Chatis P, et al. A controlled trial comparing foscamet with vidarabine for acyclovir-resistant mucocutaneous herpes simplex in the acquired immuno deficiency syndrome. The AIDS Clinical Trials Group. N Engl J Med 1991;325:551-5. Chatis PA, Miller CH, Schrager LE, Crumpacker CS. Suc cessful treatment with foscamet of an acyclovir-resistant mucocutaneous infection with herpes simplex virus in a patient with acquired immunodeficiency syndrome. N Eng) J Med 1989;320:297-300. Parris DS, Harrington JE. Herpes simplex virus variants resistant to high concentrations of acyclovir exist in clinical isolates. Antimicrob Agents Chemother 1982;22:71-7.
Acyclovir has had a dramatic impact on the treatment of herpes simplex virus (HSV) infections at all sites, including ocular. Resistance to acyclovir has been an increasing problem in severely immunocompromised patients, es pecially those with acquired immune deficiency syndrome (AIDS) 1•2 and after bone marrow transplantation, 3 and usually occurs in the setting of prolonged or multiple courses of acyclovir therapy. 3-6 Although failure to heal in clinical herpetic keratitis is a relatively common prob lem (with persistence of infection despite apparently ad equate antiviral treatment), 7 surveys have failed to show a significant rate of clinical isolates with in vitro resis tance.7.8 We report on a patient in whom the emergence ofin vitro resistance to acyclovir was associated with clin ical resistance and eventual failure of a corneal graft.
Originally received: May 22, 1992. Revision accepted: July 29, 1992. 1 Department of Ophthalmology, Duke University Medical Center, Durham. 2 Department of Internal Medicine, Duke University Medical Center, Durham. Reprint requests to Keith H. Baratz, MD, Department ofOphthalmology, Mayo Clinic, Rochester, MN 55905.
Case Report The patient is a 62-year-old, HIV-negative man with a history of well-controlled bilateral glaucoma, recurrent bilateral HSV keratouveitis, and three corneal transplantation procedures in the right eye complicated by allograft rejection, recurrent herpetic keratouveitis, and graft failure. The patient underwent an uncomplicated fourth penetrating keratoplasty in the right eye. Immediately after surgery, a drug regimen was begun, which consisted of topical prednisolone ac etate I% every 2 hours while awake, cyclosporine A 2% ointment twice daily, dexamethasone 0.05% ointment at bedtime, cyclo pentolate I% twice daily, betaxolol 0.5% twice daily, and gen tamicin 0.3% twice daily. On postoperative day 4, the cyclopen tolate and gentamicin were stopped, and the prednisolone was decreased to six times daily. Antiviral medications were not used in the immediate postoperative period. On postoperative day 14, the patient returned for routine follow-up and was found to have new keratic precipitates, an endothelial rejection line, and a central graft thickness of 0.70 mm compared with 0.66 mm I week previously. Visual acuity was 20/200, improving with pinhole to 20/80. Graft rejection was suspected, and 125 mg of methylprednisolone was admin istered intravenously. High-dose topical steroids and oral pred nisone were prescribed. Because of previous hypersensitivity to topical antiviral agents, oral acyclovir was prescribed for antiviral prophylaxis. The patient, however, did not have the prescription for acyclovir filled.
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On postoperative day 22, the patient returned with geographic epithelial defects and stromal infiltrates at the superior and in ferior graft-host junctions. Visual acuity was counting fingers, improving with pinhole to 20/400. Pachymetry was 0.72 mm centrally. The patient was hospitalized and treated with 600 mg of intravenous acyclovir every 8 hours, prednisolone acetate I% every 1 hour while awake, and 125 mg of intravenous methyl prednisolone every 6 hours. The cyclosporine A ointment was continued. Corneal culture on postoperative day 22 was positive for HSV. Initially, the clinical appearance improved. Topical steroids were decreased, and the intravenous steroid dosage was changed to 60 mg of oral prednisone every day. The acyclovir was switched to 400 mg administered orally, five times daily, on postoperative day 27. On postoperative day 28, a new epithelial defect and infiltrate developed. Culture on postoperative day 29 was again positive for HSV. Acyclovir, 600 mg intravenously every 8 hours, was resumed, and over the next several days extensive stromal ne crosis developed, which was accompanied by a Seidel-positive wound dehiscence. The epithelial defect enlarged to encompass the entire cornea and a portion of the adjacent perilimbal con junctiva despite the use of topical trifluridine I% and then idox uridine 0.5% ointment. The wound leak resolved spontaneously. Topical antiviral agents were discontinued on postoperative day 31. Repeat corneal culture on postoperative day 32 was again positive for HSV. Cyclosporine A ointment was discon tinued at this time, and topical antivirals were not restarted. Ganciclovir 300 mg intravenously every 12 hours was added to the regimen on postoperative day 36 without improvement over the next week. By postoperative day 43, the inflammation began to decrease, and the epithelial disease resolved. By postoperative day 57, complete re-epithelialization had occurred. The visual acuity in the right eye returned to 20/200 uncorrected. The pa tient was discharged on oral acyclovir 600 mg three times daily, oral prednisone 15 mg daily, and betaxolol 0.5% in both eyes twice daily. On later follow-up, the graft was considered to be failed on the basis of stromal thickening and haze. Relevant laboratory data during admission included a neg ative HIV ELISA and a normal lymphocyte subset analysis of T4 = 38%, T8 = 23% (ratio = 1.65).
Laboratory Methods The susceptibility of the HSV isolates to acyclovir and foscarnet was determined by a dye uptake assay that mea sures quantitative cytopathic effect. 9 Briefly, vero cells were challenged with the viral isolates, and the cytopathic effect at 72 hours was measured by the uptake of neutral red dye. The ID 50 was the concentration of acyclovir or foscarnet that resulted in a 50% reduction in dye uptake
compared with cell controls ( 100%) and virus controls (0%). An ID 5o > 3.0 ~g/ml of acyclovir or ID 50 > 200 ~g/ml of foscarnet was considered indicative of resistance. Vero cells infected with the HSV isolates were assayed for thymidine kinase activity by using a plaque autora diography technique as described by Martin et al. 10
Laboratory Results The initial corneal isolate obtained from the patient before the institution of intravenous therapy was susceptible to acyclovir and positive for thymidine kinase activity (Table I). Isolates obtained later in the patient's hospital course were resistant to acyclovir and deficient in thymidine ki nase. All viral isolates were susceptible to foscarnet.
Discussion This case demonstrates the emergence of acyclovir-resis tant HSV keratouveitis while receiving therapy, associated with clinical failure of a corneal graft. This patient was not severely immunocompromised, as has been the case in most patients reported with acyclovir-resistant HSV infections. However, he had undergone a corneal graft procedure and was receiving oral steroids, topical steroids, and topical cyclosporine. These factors may have con tributed to the development of resistance. This patient resembles previously described patients with acyclovir resistant non ocular HSV in that he has a history of pro longed HSV infection, multiple exposures to acyclovir, and use of steroids. This case is unique in that the patient did not have AIDS, was not severely immunocompro mised, and had an ocular site of infection. Review of the literature showed only two previous reports ofocular HSV infection that document in vitro resistance to acyclovir. In one study, reduced sensitivity to acyclovir was identified in 3 of 40 isolates from patients with primary infections acquired in the community and without a previous history of treatment with acyclovir; no clinical resistance was noted. 11 The second report is of a 15-year-old girl with AIDS and herpetic keratitis, who did not respond to high dose oral acyclovir, topical trifluridine, topical idoxuri dine, and topical vidarabine, but eventually improved with topical alpha-interferon; in vitro resistance to acyclovir was identified. 12
Table 1. Antiviral Susceptibility and Thymidine Kinase Activity Acyclovir Isolate
IDso (~tg/ml) ± SE
POD22 POD29 POD32
0.27 ± 0.18 (S) 9.4 ± 6.51 (R) 15.2 ± 7.4 (R)
TK = thymidine kinase; S = susceptible; R = resistant.
1806
Foscarnet IDso
(~tgfml)
± SE
56± 5.8 (S) 37 ± 11 (S) 20 ± 40 (S)
TK Activity Positive Deficient Deficient
Sonkin et al · Acyclovir-resistant HSV Keratouveitis after PK Acyclovir is phosphorylated by HSV-specific thymidine kinase, and is then further phosphorylated to acyclovir triphosphate by host cell kinases. 13- 15 The triphosphate is the active form of acyclovir that inhibits the viral DNA polymerase and is incorporated into the viral DNA chain. 16- 18 Most clinical isolates ofacyclovir-resistant HSV have been deficient in thymidine kinase (TK-). 1·19·20 TK strains exhibit decreased virulence in animal mod els,21-23 and early reports suggested that TK- mutants have reduced clinical virulence. 3 However, recent reports have noted severe mucocutaneous disease due to TK strains in patients with AIDS or after bone marrow trans plantation.1·19 Our patient had a TK- acyclovir-resistant strain, which caused severe keratouveitis and contributed to graft failure. Resistant strains of HSV with normal in duction of thymidine kinase (TK +) also have been iso lated. These TK+ mutants either have an altered DNA polymerase, which is not susceptible to acyclovir-tri phosphate, 24 or a thymidine kinase enzyme with altered substrate specificities (i.e., less able to phosphorylate acy clovir).25,26 Prophylactic acyclovir for herpes simplex virus kera touveitis or corneal grafting has received relatively little attention in the literature. Prophylaxis for nonocular HSV has been advocated for patients considered to be at high risk, such as seropositive bone marrow transplant pa tientsY Resistance, however, can emerge on exposure to acyclovir and has occurred with prophylaxis in other set tings.19 Low-dose prophylactic acyclovir has actually been shown to select for resistant virus in animal studies. 21 En glund et al 19 reported that low-dose therapy during a virus free period antedated the isolation of resistant virus in one patient. Furthermore, long-term oral or low-dose suppressive therapy in symptomatic patients may also potentiate selection of resistant strains. When using pro phylactic acyclovir after penetrating keratoplasty, the emergence or persistence of active infection should alert the ophthalmologist that a resistant infection may be present. Definite therapeutic recommendations for ocular dis ease due to acyclovir-resistant HSV cannot be made be cause of the limited clinical experience. In addition to topical antiviral agents (which remain an integral part of clinical management), there are several possible alternate therapies available. Foscarnet is becoming a drug ofchoice for acyclovir-resistant mucocutaneous disease in AIDS patients. Controlled trials have shown foscarnet to be more effective and less toxic than vidarabine in this setting_28-30 Foscarnet is generally well-tolerated in these studies, al though renal and other toxicities are observed in some patients. Foscarnet is a pyrophosphate analog that inhibits HSV DNA polymerase without activation by viral thy midine kinase, 1 and it remains effective against the more common TK- resistant mutants. 1·29 High-dose, contin uous, intravenous acyclovir also has been effective in treating mucocutaneous disease due to resistant HSV. 2·19 However, high-dose intermittent intravenous acyclovir was not effective in our patient. Discontinuation of acy clovir therapy also has been used therapeutically in non ocular infections because it can result in the return of
sensitive virus, 19 but this approach may not be practical in ocular settings. Ganciclovir is structurally similar to acyclovir and also requires phosphorylation by HSV thy midine kinase to become activated. It is not a rational choice for the treatment of acyclovir-resistant HSV, and it has not been effective when used. 1 Patients receiving ganciclovir for acyclovir-resistant HSV do not improve clinically, nor do these viral isolates show in vitro suscep tibility to ganciclovir. 1 Our patient seemed to improve after onset of ganciclovir therapy. In vitro susceptibility and thymidine kinase assay results were not immediately available to aid in therapeutic decisions. However, given the mechanism of action of the drug and the fact that acyclovir-resistant HSV infections may undergo sponta neous healing, 31 it is unlikely that ganciclovir helped our patient. Although the role of ganciclovir in the course of this patient's disease is unclear, this drug should not be a primary alternative. Lastly, topical alpha-interferon has been used successfully to treat acyclovir-resistant HSV keratouveitis in a patient with AIDS. 12 Ophthalmologists should be aware of the potential for acyclovir-resistant HSV infections after penetrating ker atoplasty, especially in those patients with previous HSV infections or exposure to acyclovir. Rapid procedures for the determination of HSV acyclovir susceptibility are re ported and should be made more widely available. 19 Ra tional alternate therapies are available for acyclovir-resis tant HSV. Acknowledgment. The authors thank Edgar L. Hill, PhD,
Department of Virology, Burroughs Wellcome Co, Research Triangle Park, NC, for in vitro drug susceptibility testing and thymidine kinase assays.
References 1. Erlich KS, Mills J, Chatis P, et al. Acyclovir-resistant herpes simplex virus infections in patients with the acquired immu nodeficiency syndrome. N Eng) J Med 1989;320:293-6. 2. Engel JP, Englund JA, Aetcher CV, Hill EL. Treatment of resistant herpes simplex virus with continuous-infusion acyclovir. JAMA 1990;263: 1662-4. 3. Wade JC, McLaren C, Meyers JD. Frequency and signifi cance of acyclovir-resistant herpes simplex virus isolated from marrow transplant patients receiving multiple courses of treatment with acyclovir. J Infect Dis 1983;148: 1077 82. 4. Crumpacker CS, Schnipper LE, Marlowe SI, et al. Resistance to antiviral drugs ofherpes simplex virus isolated from a patient treated with acyclovir. N Eng) J Med 1982;306:343-6. 5. Bums WH, Saral R, Santos GW, et al. Isolation and char acterisation of resistant herpes simplex virus after acyclovir therapy. Lancet 1982;1:421-3. 6. Sibrack CD, Gutman LT, Wilfert CM, et al. Pathogenicity of acyclovir-resistant herpes simplex virus type 1 from an immunodeficient child. J Infect Dis 1982;146:673-82. 7. Menage MJ, de Clercq E, van Lierde A, et al. Antiviral drug sensitivity in ocular herpes simplex virus infection. Br J Ophthalmol 1990;74:532-5. 8. Mori Y, Inoue Y, Shimomura Y, Manabe R. In vitro sen sitivity to antiviral agents of herpes simplex viruses isolated from patients with herpetic keratitis. Nippon Ganka Gakkai Zasshi 1990;94:484-7.
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Ophthalmology
Volume 99, Number 12, December 1992
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