PEDIATRICS Vol. 108 No. 2 August 2001, pp. 230-238

Safety and Efficacy of High-Dose Intravenous Acyclovir in the Management of Neonatal Herpes Simplex Virus Infections

David W. Kimberlin, MD^*, Chin-Yu Lin, PhD^*, Richard F. Jacobs, MD, Dwight A. Powell, MD^§, Lawrence Corey, MD, William C. Gruber, MD^¶, Mobeen Rathore, MD^#, John S. Bradley, MD^**, Pamela S. Diaz, MD, Mary Kumar, MD^§§, Ann M. Arvin, MD^||, Kathleen Gutierrez, MD^||, Mark Shelton, MD^¶¶, Leonard B. Weiner, MD^##, John W. Sleasman, MD^***, Teresa Murguía de Sierra, MD, Stephen Weller^§§§, Seng-Jaw Soong, PhD^*, Jan Kiell, RN^*, Fred D. Lakeman, PhD^*, Richard J. Whitley, MD^*, and the National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group^a

From the ^* Department of Pediatrics, University of Alabama at Birmingham, Alabama;  Department of Pediatrics, University of Arkansas, Little Rock, Arkansas; ^§ Department of Pediatrics, Ohio State University, Columbus, Ohio;  Department of Medicine, University of Washington, Seattle, Washington; ^¶ Department of Pediatrics, Vanderbilt University, Nashville, Tennessee; ^# Department of Pediatrics, University of Florida Health Science Center, Jacksonville, Florida; ^** Department of Pediatrics, University of California San Diego, California;  Chicago Department of Public Health, Chicago, Illinois; ^§§ Department of Pediatrics, Case Western Reserve, Cleveland, Ohio;^|| Department of Pediatrics, Stanford University, Stanford, California; ^¶¶ Cook Children's Medical Center, Fort Worth, Texas; ^## Department of Medicine, State University of New York, Syracuse, New York; ^*** Department of Pediatrics, University of Florida, Gainesville, Florida;  Hospital Infantil de Mexico, Mexico City, Mexico; and ^§§§ Glaxo Wellcome Inc, Research Triangle Park, North Carolina.

	ABSTRACT

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Objective.  The objective of this investigation was to establish the safety of high-dose (HD) acyclovir for the treatment of neonatal herpes simplex virus (HSV) disease. In addition, an estimate of therapeutic efficacy was sought, both with respect to mortality and to morbidity. Virologic efficacy of HD acyclovir was also assessed.

Participants.  Infants who were 28 days old and whose disease was considered to be caused by HSV were enrolled in this study. Patients with central nervous system (CNS; N = 28) or disseminated (N = 41) HSV infection were offered participation in the trial. A small number of patients with HSV disease limited to the skin, eyes, or mouth (SEM; N = 10) or whose disease was clinically consistent with HSV but who did not have virologic confirmation of infection (N = 9) also were enrolled on a compassionate basis. Only patients with virologically confirmed HSV disease were included in efficacy analyses. All enrolled patients were included in safety analyses.

Methods.  The study was an open-label evaluation of intravenous acyclovir at dosages higher than the 30 mg/kg/d standard dosage approved by the US Food and Drug Administration. The first 16 patients enrolled received intermediate-dose (ID) acyclovir (45 mg/kg/d), and the next 72 patients received HD acyclovir (60 mg/kg/d). Acyclovir was administered in 3 divided daily doses for 21 days. Neonates were assessed prospectively throughout treatment and at scheduled follow-up visits for the first 4 years of life. Data were compared with those of a previous National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group trial in which patients received standard-dose (SD) acyclovir for 10 days and in which identical methods (with the exception of acyclovir dosage and duration of therapy) were used.

Results.  Six (21%) of 29 HD acyclovir recipients whose HSV disease remained localized to the SEM or CNS experienced neutropenia. One of the 6 had an absolute neutrophil count <500/mm³, and 5 patients had an absolute neutrophil count (ANC) between 500/mm³ and 1000/mm³. In all 6 cases, the ANC recovered during continuation of acyclovir at the same dosage or after completion of acyclovir therapy, and there were no apparent adverse sequelae of the transient neutropenia. No other drug-related adverse events were reported among ID or HD recipients, and no other laboratory aberrations could be correlated specifically with antiviral therapy. The survival rate for the patients with disseminated HSV disease treated with HD acyclovir was significantly higher than for those in the previous study treated with SD acyclovir, with an odds ratio (OR) of 3.3 (95% confidence interval [CI]: 1.4-7.9). For patients with CNS disease, however, survival rates were similar for the HD and SD groups. To assess the effect of HD acyclovir on survival for the entire population with neonatal HSV disease, the Cox proportional hazards regression analysis was performed with stratification for disease category (CNS versus disseminated). In performing this analysis, differences in mortality for each disease category were weighted to allow statistical comparison of the treatment dosage groups (HD, ID, and SD). This analysis indicated that the survival rate for patients treated with HD acyclovir was statistically significantly higher than for patients treated with SD acyclovir (OR: 3.3; 95% CI: 1.5-7.3). Recipients of HD acyclovir had a borderline significant decrease in morbidity compared with SD recipients, after stratification for the extent of disease (SEM vs CNS vs disseminated) and controlling for the potential confounding factors of HSV type (HSV-1 vs. HSV-2), prematurity, and disease severity (seizures). Patients treated with HD acyclovir were 6.6 times (adjusted OR; 95% CI: 0.8-113.6) as likely to be developmentally normal at 12 months of age as patients treated with SD therapy.

Conclusion.  These data support the use of a 21-day course of HD (60 mg/kg/d) intravenous acyclovir to treat neonatal CNS and disseminated HSV disease. Throughout the course of HD acyclovir therapy, serial ANC determination should be made at least twice weekly. Decreasing the acyclovir dosage or administering granulocyte colony-stimulating factor should be considered if the ANC remains below 500/mm³ for a prolonged period.  Key words:  newborn, herpes simplex virus, acyclovir.

With the advent of safe and effective antiviral therapy during the past 2 decades for treating neonatal herpes simplex virus (HSV) disease, significant improvements in mortality and morbidity have been achieved. Vidarabine was the first commercially available drug for treating neonatal HSV disease; pivotal trials demonstrating its efficacy were reported in the early 1980s.^1,2 By the end of the 1980s, a controlled, comparative study of vidarabine and acyclovir demonstrated that both antiviral compounds were equally efficacious for treating neonatal HSV disease.³ Because of its ease of administration, intravenous acyclovir quickly supplanted vidarabine as the standard of care for managing neonatal HSV infections. In accordance with its long-standing use in neonatal HSV disease, acyclovir was licensed by the US Food and Drug Administration for this indication in June 1998.

Despite these advances, mortality and morbidity in neonatal HSV disease remain unacceptably high. Efforts to decrease the likelihood of relapse of neonatal HSV disease after completion of intravenous antiviral therapy have resulted in the lengthening of treatment courses from 10 days to 14-21 days.^3,4 Additionally, an evaluation of higher dosing regimens of acyclovir was undertaken in an effort to improve the mortality and morbidity associated with neonatal HSV disease. In the study presented herein, HSV-infected neonates receiving acyclovir at dosages of 45 mg/kg/d (intermediate-dose [ID] acyclovir) and 60 mg/kg/d (high-dose [HD] acyclovir) administered parenterally in 3 divided doses daily for 21 days were evaluated for safety and toxicity. Additionally, estimates of therapeutic efficacy were made, with comparisons to patients from the vidarabine/acyclovir trial³ who received intravenous acyclovir at 30 mg/kg/d (standard-dose [SD] acyclovir) for 10 days.

	METHODS

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Study Population

Infants who were 28 days old and whose disease was considered to be caused by HSV were enrolled in this study. The disease classifications of central nervous system (CNS) infection, disseminated infection, and infection limited to the skin, eyes, or mouth (SEM) were based on extent of disease and were identical to those used in previous Collaborative Antiviral Study Group (CASG) studies.³ Patients with CNS (N = 28) or disseminated (N = 41) HSV infection were offered participation in this trial. A small number of patients with SEM HSV disease (N = 10) or whose disease was clinically consistent with HSV but who did not have virologic confirmation of HSV infection (N = 9) also were enrolled on a compassionate basis at the discretion of the participating investigator. Such compassionate enrollment reflected a desire to gather additional information on the use of HD acyclovir and was not related to a greater severity of the patients' illness. Thus, by design the proportion of patients in this study with CNS or disseminated HSV disease exceeds that reported in previous studies of neonatal HSV,³ where all patients (including those with SEM involvement only) were actively recruited for study participation. Only patients with virologically confirmed HSV disease, defined as a positive viral culture from any site or a positive HSV polymerase chain reaction determination from cerebrospinal fluid (CSF), were included in efficacy analyses (N = 79). All enrolled patients were included in the safety analyses (N = 88).

Additional requirements for study enrollment included a weight of 1200 g and a gestational age of >32 weeks. Patients receiving other antiviral drugs were excluded from participation in this trial, as were patients with imminent demise.

Study Design and Objectives

Informed consent, obtained from the infant's parent(s) or legal guardian(s), was required for study entry. The study was an open-label evaluation of intravenous acyclovir at dosages greater than SD (30 mg/kg/d). Acyclovir was administered intravenously in 3 divided doses daily for 21 days. Acyclovir was provided by Glaxo Wellcome (Research Triangle Park, NC) for the purpose of this study.

Objectives of this phase 2 trial included determining whether an acyclovir dosage higher than SD was safe and well tolerated in neonates. The pharmacokinetics of acyclovir when administered at greater than SD were evaluated. Mortality and morbidity of treated neonates with CNS or disseminated HSV disease were assessed and compared with those of patients who had received SD acyclovir for 10 days in the earlier CASG trial.³ Virologic effects of ID and HD acyclovir on rates of viral excretion were also determined.

Clinical Observations

Neonates were assessed prospectively throughout the course of ID or HD acyclovir administration and in scheduled follow-up visits for the first 4 years of life. Findings were recorded on standardized case record forms. Baseline demographic data were gathered at the time of study enrollment. Clinical evaluation of patients during hospitalization included assessment of neurologic manifestations (focal seizures, generalized seizures, poor suck, poor feeding, spasticity, opisthotonus, microcephaly, and hydranencephaly), ocular manifestations (conjunctivitis, chorioretinitis, dendritic or geographic lesions, and strabismus), cutaneous manifestations (skin vesicle formation, petechiae, and purpura), pulmonary manifestations (HSV pneumonia and ventilatory support for any reason), visceral organ involvement (hepatomegaly, splenomegaly, and necrotizing enterocolitis), and evidence of bleeding diatheses (disseminated intravascular coagulopathy).

After discharge from the hospital, patients were followed at 6, 12, 24, 36, and 48 months of age. Assessment of function was made at each of these visits. Function was assessed as normal, impaired but able to live at home, institutionalized, or deceased. Impairment was quantitated as mild (ocular sequelae [recurrent keratoconjunctivitis], speech delay, or mild motor delay [in the absence of hemiparesis]); moderate (hemiparesis, persistent seizure disorder, or <3-month developmental delay); or severe (microcephaly, spastic quadriplegia, blindness or chorioretinitis, or >3-month developmental delay). These definitions have been used in previous studies of neonatal HSV conducted by the CASG.³

Laboratory Observations

Virus isolation and typing Specimens for HSV isolation were obtained from the oropharynx, CSF, conjunctivae, and skin vesicles (if present).^2,5 In addition, serial cultures from the oropharynx and skin vesicles were obtained throughout antiviral therapy. These samples were inoculated onto cell cultures suitable for virus isolation at each participating institution. Isolates of HSV were typed with monoclonal antibodies as previously described.⁶

Safety and Toxicity Measures Monitoring for adverse events was performed daily, and laboratory assessments for safety and toxicology were performed on study days 1, 3, 7, 10, 14, 17, 21, and 28. Laboratory analyses included complete blood counts, platelet counts, reticulocyte counts, and measurements of aspartate aminotransferase, bilirubin, uric acid, creatinine, and blood urea nitrogen. Toxicity assessments were quantitated using the Division of AIDS Toxicity Tables.

Antibody Determination Antibody determinations were performed using an enzyme-linked immunosorbent assay.⁵

Pharmacokinetics Plasma acyclovir concentrations were measured in 13 patients, 11 of whom received ID acyclovir and 2 of whom received HD acyclovir. Specimens for plasma drug concentrations were obtained early in treatment (between days 4 and 7, although primarily on days 4 and 5) and at the end of therapy (between days 20 and 22, except for 1 patient whose concentrations were determined on day 15). Seven of the 13 patients had 5 or fewer data points available for parameter estimation for at least 1 of their plasma drug concentration determinations. Pharmacokinetic parameters are estimated from NONLIN model fits of individual patient data. Because of sparsity, noncompartmental analysis was not possible. Determination of acyclovir plasma concentrations was performed at Glaxo Wellcome using a radioimmunoassay.⁷

Statistical Analysis

Fisher's exact test was used to compare the differences in toxicity between the patients treated with ID and HD acyclovir. The Cox proportional hazards model was used to compare the survival distributions between the HD and SD acyclovir groups, with stratification for the disease categorization and with adjustments for HSV type and indicators of disease severity. The Fisher's exact tests were used to compare the morbidity outcomes according to the extent of disease. The logistic regression analysis using conditional maximum likelihood inference⁸ with stratification of disease category was used to compare the morbidity outcomes between the HD and SD acyclovir groups (hypothesis tests are performed by exact conditional score tests) and to calculate the adjusted odds ratio (OR) of abnormal development at 12 months of life between the HD and SD acyclovir groups, with adjustment for the extent of disease, HSV type, and prematurity. The log-rank test was applied for comparisons of viral shedding.

	RESULTS

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Population Characteristics

Eighty-eight neonates were enrolled in the study and received intravenous acyclovir at dosages greater than SD (30 mg/kg/d). All 88 patients were treated for 21 days. Neonates were enrolled from 14 institutions between 1989 and 1997. The first 16 patients were enrolled in 1989 and 1990 and received ID acyclovir (45 mg/kg/d). The other 72 patients were enrolled between 1990 and 1997 and received HD acyclovir (60 mg/kg/d). Of the 88 patients, 9 neonates (3 in the ID group and 6 in the HD group) presented with disease clinically consistent with neonatal HSV but did not have virologic confirmation of HSV infection. For this reason, these 9 patients are not included in the efficacy analyses but are included in the safety analyses.

Demographic characteristics of the neonates with virologically confirmed HSV disease are presented in Table 1. The characteristics of the 79 neonates who received either ID or HD acyclovir are compared with those of the 107 neonates who received SD acyclovir in the previous CASG trial.³ The groups were similar except in extent of disease, where the preferential enrollment of patients with CNS and disseminated HSV disease in the high-dose study accounts for the differences seen.

Safety Analyses

A summary of laboratory abnormalities that developed during intravenous acyclovir therapy is presented in Table 2. The laboratory abnormalities seen in the ID and HD groups were similar and were not statistically significant by the Fisher's exact test. Elevations of creatinine, bilirubin, and aspartate aminotransferase (AST) occurred only in patients with disseminated HSV disease, as did platelet counts of 100 000. Abnormally low hemoglobin concentrations were reported only in very ill neonates who needed frequent phlebotomies to monitor their clinical course. Although each of these laboratory abnormalities could be explained by the patients' underlying medical conditions, the available data do not allow a final determination of causality (underlying disease vs HD acyclovir toxicity vs additive effect of severe disease and HD acyclovir regimen).

In contrast, neutropenia occurred both in patients with severe systemic disease (disseminated patients) and in patients whose disease was localized (CNS and SEM patients; Table 2). For patients with disseminated HSV disease, the development of neutropenia could be secondary to widespread viral replication, including within the bone marrow. For patients with localized disease (CNS or SEM), however, it is harder to attribute the development of neutropenia to the underlying viral process. Thus, to more fully assess neutropenia as a potential toxicity of HD acyclovir therapy, patients with apparently localized disease were evaluated. Of the 38 enrolled patients with disease localized to the CNS or SEM, 29 received HD acyclovir and had absolute neutrophil count (ANC) values recorded both at the beginning of therapy and during intravenous acyclovir (Table 3). Six (21%) of these 29 patients developed neutropenia (ANC 1000/mm³) during HD acyclovir therapy. Graphs of the neutropenia experienced by these 6 patients, by study day, demonstrate that in most cases neutropenia occurred early in the course of treatment (Fig 1). Five of these patients developed ANCs between 500/mm³ and 1000/mm³, and 1 developed an ANC <500/mm³. Four of the patients were term infants, and 2 were preterm. In all 6 cases, the neutrophil count recovered (>1000/mm³) during continuation of acyclovir at the same dosage or after completion of acyclovir therapy. There were no apparent adverse sequelae of the transient neutropenia experienced by these 6 patients.

View larger version (23K): [in this window] [in a new window]   Fig. 1.   Neutropenia in patients with SEM and CNS HSV receiving HD acyclovir.

Efficacy Analyses

Mortality

Disseminated Disease As illustrated in Fig 2A, the 24-month mortality rate among patients with disseminated disease receiving 21 days of HD acyclovir was 31%, compared with 57% for patients treated with ID acyclovir for 21 days and 61% for patients who received SD acyclovir for 10 days in the earlier CASG trial.³ The Cox proportional hazards regression analysis indicated that the survival rate of patients with disseminated HSV disease treated with HD acyclovir was significantly higher than that of patients treated with SD acyclovir (P = .0064), with OR = 3.3 (95% confidence interval [CI]: 1.4-7.9). The difference in the survival rate between patients with disseminated HSV disease treated with ID and SD acyclovir was not statistically significant (P = .729; OR: 1.2; 95% CI: 0.4-3.9).

View larger version (26K): [in this window] [in a new window]   Fig. 2.   Mortality in patients with A) disseminated disease and B) CNS disease.

CNS Disease The mortality rate at 24 months for patients with CNS disease receiving 21 days of HD acyclovir was 6% (Fig 2b), compared with 20% for patients who received ID acyclovir for 21 days and 19% for patients who received SD acyclovir for 10 days in the earlier CASG trial.³ The Cox proportional hazards regression analysis indicated that the differences in survival rates among patients treated with HD, ID, or SD acyclovir were not significantly different.

Overall In an effort to assess whether HD acyclovir improved patients' survival regardless of disease classification, the Cox proportional hazards regression analysis was performed with stratification for disease category (CNS versus disseminated). In performing this analysis, the differences in mortality for each of these disease categories were weighted to allow for statistical comparison of the treatment groups (HD, ID, and SD therapy). This analysis indicated that the survival rate for patients treated with HD acyclovir was statistically significantly higher than that for patients treated with SD acyclovir (P = .0035; OR = 3.3; 95% CI: 1.5-7.3) but not significantly different from the survival rate of patients treated with ID acyclovir (P = .846; OR = 1.1; 95% CI: 0.4-3.1). The mean time between onset of disease symptoms and initiation of therapy was similar between the 2 time periods during which the SD patients and the HD patients were treated,¹⁰ suggesting that differences in onset of treatment cannot explain the disparity in survival.

Morbidity Morbidity after 12 months of life for surviving patients with known outcomes who received HD acyclovir for 21 days is illustrated in Fig 3. Comparative data collected in an identical manner from patients in the earlier CASG controlled trial who received SD acyclovir for 10 days³ also are shown.

View larger version (26K): [in this window] [in a new window]   Fig. 3.   Morbidity among patients with known outcomes after 12 months of life.

Virologic Efficacy The median duration of viral shedding from skin vesicles and mucosal sites for patients receiving SD, ID, and HD acyclovir was 5, 8, and 5 days, respectively. There were no substantive differences with respect to clearance of virus from skin vesicles and mucosal sites as a function of the acyclovir dosage used, and the differences are not statistically significant (P = .4101).

Pharmacokinetic Evaluation

Serum was obtained from 13 patients near the beginning or at the end of intravenous acyclovir therapy to determine acyclovir concentration; 11 of them received ID (45 mg/kg/d) and 2 received HD (60 mg/kg/d) acyclovir. For the 2 HD recipients, the mean steady-state acyclovir peak concentration (C_max) and the mean steady-state acyclovir trough concentration (C_min) were determined after normalization to dosages of 15 mg/kg. Thus, all pharmacokinetic parameters reported herein are based on acyclovir dosages of 15 mg/kg. Evaluation of acyclovir concentrations in CSF was not performed. None of the 11 patients experienced grade 3 or 4 creatinine toxicity, using the Division of AIDS Toxicity Tables, before or during intravenous acyclovir therapy.

The mean (±SD) C_max was 18.82 ± 5.22 µg/mL (range, 9.82-28.25 µg/mL). The mean (±SD) C_min was 3.18 ± 2.62 µg/mL (range, 0.60-9.95 µg/mL). The mean (±SD) acyclovir half-life (t_1/2) was 3.03 ± 1.06 hours, with the mean (±SD) acyclovir clearance normalized by weight being 4.42 ± 1.57 mL/min/kg. C_max, C_min, and t_1/2 all decreased with increasing patient age, whereas acyclovir clearance increased with increasing patient age. These findings are comparable to other published data.^11,12

Antibody Determination

To determine whether HD acyclovir impeded the development of an appropriate antibody response to HSV, sera for HSV antibody determinations were obtained from infants with virologically confirmed HSV disease. Seven patients had 2 or more specimens available for serologic analysis (1 from the beginning of therapy or during therapy and the other 6 months to 18 months after completion of acyclovir administration). Four of these 7 patients had a fourfold or greater rise in serum antibody titers between these 2 time points. Although a fourfold increase was not seen in the remaining 3 patients, all 3 had high antibody titers when initially tested (1:1600) and maintained the high titers at follow-up.

Of the 18 patients with virologically confirmed HSV infection who had available serologic results after completion of acyclovir therapy, 17 (94%) had detectable antibody present between 6 months and 18 months after onset of HSV disease. One patient had negative serology at both 6- and 12 month follow-ups. This patient had culture-proven disseminated disease caused by HSV-2 and was developing normally at the 6-, 12-, and 24-month follow-up examinations.

	DISCUSSION

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The results reported herein support the use of HD acyclovir for 21 days in managing neonatal CNS and disseminated HSV disease. Although this was not a randomized controlled investigation, mortality rates after stratification for the disease category (CNS vs disseminated) are significantly lower (P = .0035) than those of patients treated in an earlier study with SD acyclovir for 10 days.³ The relative impact of HD acyclovir on reduced mortality remains incompletely understood, given that other factors have also changed since completion of the last major study of the treatment of neonatal HSV disease.³ Specifically, the duration of therapy is now longer (21 days vs 10 days), and other improvements have been made in the critical care support that these gravely ill patients receive (eg, high frequency ventilation, and improved management of hemodynamic instability). However, several findings support the conclusion that improved survival relates primarily to the acyclovir dosage used. First, the calendar year of treatment was not significantly associated with mortality, minimizing the impact on survival of technologic advances that occurred between the time periods in which the HD and SD patients were treated. Second, duration of illness before initiation of therapy was similar between the SD and the HD recipients, eliminating the possibility that the improved survival of the HD recipients resulted from more rapid initiation of therapy. Third, the demographic characteristics of the treatment groups were similar, regardless of time period in which they were treated.¹⁰

Statistical interpretation of the efficacy of ID acyclovir is limited by the small numbers of patients in this treatment cohort. This fact accounts for the very wide confidence intervals reported herein for morbidity and mortality analyses involving the ID recipients. Similarly, the numbers of patients lost to long-term follow-up decreased the numbers of participants with known outcomes (morbidity report in the "Efficacy Analyses" section). The lower numbers of patients with known outcomes could explain why patients receiving HD acyclovir had only a borderline significant diminution in morbidity as compared with SD acyclovir recipients. Although the statistical analyses used can to some degree adjust for the smaller numbers of patients with known outcomes, they cannot completely eliminate the potential for bias that may be introduced when relatively large numbers of patients are lost to long-term follow-up.

The primary apparent toxicity associated with the use of HD acyclovir is neutropenia. Fully 21% of patients with localized disease (CNS or SEM) treated with HD acyclovir developed an ANC of 1000/mm³. Although it is difficult to ascribe the neutropenia experienced by these patients to their underlying localized disease process, it is possible that the low ANCs reflect a margination process rather than true drug toxicity. Regardless, it is reassuring that the majority of these patients had ANCs between 500/mm³ and 1000/mm³, that none of the patients experienced any reported adverse sequelae as a consequence of their neutropenia, and that the neutropenia resolved either during continuation of HD acyclovir or after its cessation. Only 1 well-documented case report of parenteral acyclovir-induced neutropenia has appeared in the literature.¹³ Of the other reports in the literature of neutropenia associated with parenteral acyclovir, the neutropenia may have resulted from the patients' underlying diseases or may have been related to other medications they were receiving.^14-17 Neutropenia has been documented in almost half of infants receiving long-term suppressive oral acyclovir therapy after resolution of their acute neonatal HSV disease.¹⁸ It is prudent to monitor neutrophil counts at least twice weekly throughout HD acyclovir therapy, with consideration being given to decreasing the acyclovir dosage or administering granulocyte colony-stimulating factor if the ANC remains below 500/mm³ for a prolonged period of time. Other laboratory values followed during HD acyclovir therapy must be chosen to reflect the degree of organ involvement each patient is manifesting.

Acyclovir's potential nephrotoxicity is well described in the literature.¹⁹ However, only 4 (6%) of 64 HD acyclovir recipients in the current study developed grade 3 or 4 toxicity. Furthermore, all 4 of these patients had disseminated HSV disease, which could either contribute to or account for this toxicity. The hydration status of all study patients was followed closely, which also could have helped to minimize the observance of nephrotoxicity. Guidelines for administering intravenous acyclovir in neonates with impaired renal function have been previously published and apply to the use of HD acyclovir as well.²⁰ In patients with moderately reduced creatinine clearance (serum creatinine 0.8-1.1 mg/dL [70-100 µmol/L]), the dosage (20 mg/kg) should be administered every 12 hours, and for neonates with reduced creatinine clearance (serum creatinine 1.2-1.5 mg/dL [110-130 µmol/L]) it should be administered every 24 hours. In renal failure (serum creatinine >1.5 mg/dL [130 µmol/L], or urine output <1 mL/kg/h), the dosage should be halved (10 mg/kg) and given every 24 hours.

The use of HD acyclovir did not impede development of an adequate antibody response in those assessed; all patients for whom paired sera were available for analysis either achieved a high absolute antibody titer or had a fourfold or greater rise in serum antibody titers. Furthermore, 17 of 18 patients with available serologic results 6 to 18 months after completion of acyclovir therapy had detectable antibodies. The fact that this seropositivity persisted beyond 6 months of age suggests that the HSV antibodies are infant-derived rather than maternal in origin.

In conclusion, these uncontrolled data support the use of HD (60 mg/kg/d) acyclovir administered for 21 days to treat neonatal CNS and disseminated HSV disease. Additionally, HD acyclovir administered for 14 days has recently been recommended by the American Academy of Pediatrics Committee on Infectious Diseases to treat neonatal SEM HSV disease.²¹ Throughout the course of HD acyclovir therapy, serial determinations of ANC should be made.

	ACKNOWLEDGMENTS

This study was supported under contract with the Virology Branch, Division of Microbiology and Infectious Diseases of the NIAID, NO1-AI-15113 and NO1-AI-62554, and by grants from the General Clinical Research Center Program (RR-032) and the State of Alabama.

Members of the NIAID CASG include C. Laughlin, W. Dempsey, T. Gaither, and D. Morens, National Institutes of Health, Bethesda, Maryland; R. Whitley, J. Gnann, F. Lakeman, S.-J. Soong, D. Kimberlin, C.-Y. Lin, S. Stagno, and R. Pass, University of Alabama at Birmingham; M. Abzug and H. Rotbart, University of Colorado HSC, Denver; S. Adler, Medical College of Virginia, Richmond; A. Ahmed, Carolinas Medical Center, Charlotte, North Carolina; S. Alter, Wright State University, Dayton, Ohio; F.Y. Aoki, University of Manitoba-Winnipeg, Canada; A. Arvin, C. Prober, K. Gutierrez, Stanford University, Stanford, California; K. Belani, Park Nicollet Medical Center, Minneapolis, Minnesota; J. Bernstein, VA Medical Center, Dayton, Ohio; M. Boeckh, Fred Hutchinson Cancer Research Center, Seattle, Washington; J. Bradley, M. Sawyer, S. Spector, and W. Dankner, University of California, San Diego; T. Chonmaitree, University of Texas, Galveston; J. Christenson, University of Utah Medical Center, Salt Lake City; A. Cohen-Abbo, Connecticut Children's Medical Center, Hartford; L. Corey and L. Frenkel, University of Washington, Seattle; M. Cowan, University of California, San Francisco; A. Cross, University of Maryland, Baltimore; G. Demmler and R. Atmar, Baylor College of Medicine, Houston, Texas; P. Dennehy, Rhode Island Hospital, Providence; P. Diaz, Chicago Department of Health, Illinois; K. Edwards, Vanderbilt University, Nashville, Tennessee; J. Englund, University of Chicago, Illinois; R. Finberg, Dana Farber Cancer Institute, Boston, Massachusetts; S. Fowler, Medical University of South Carolina, Charleston; P. Gross, Hackensack University Medical Center, New Jersey; F. Hayden, University of Virginia Medical Center, Charlottesville; P. Hughes, Albany Medical Center, New York; R. Jacobs, N. Tucker, and C. Bower, Arkansas Children's Hospital, Little Rock; J. Kahn, Yale-New Haven Hospital, Connecticut; H. Keyserling, Emory University, Atlanta, Georgia; J. Kinney, Baylor University Medical Center, Dallas, Texas; A. Kovacs, University of Southern California, Los Angeles; M.L. Kumar, MetroHealth Medical Center, Cleveland, Ohio; C. Leach, University of Texas, San Antonio; D. Lehman, Cedars-Sinai Medical Center, Los Angeles, California; R. Lichenstein, University of Maryland, Baltimore; D. Malis, Brooke Army Medical Center, San Antonio, Texas; C. Mani, Marshall University, Huntington, West Virginia; C. McCarthy, Maine Medical Center, Portland; P. Mehta, University of Florida, Gainesville; C. Meissner, New England Medical Center, Boston, Massachusetts; G. Mertz, University of New Mexico, Albuquerque; L. Miedzinski, University of Alberta, Edmonton, Canada; H. Milczuk, Oregon Health Sciences University, Portland; C. Miller, Johns Hopkins University, Baltimore, Maryland; J. Modlin and T. Rhodes, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire; A. Moscona, Mount Sinai Medical Center, New York, New York; S. Nagy-Agren, Veterans' Affairs Medical Center, Salem, Virginia; A. Palmer, University of Mississippi, Jackson; C. Paya, Mayo Clinic, Rochester, Minnesota; W. Pomputius, St Joseph's Hospital, Tampa, Florida; D. Powell, Ohio State University, Columbus; M. Rathore, S. Midani, and A. Alvarez, University of Florida, Jacksonville; J. Robinson and W. Vaudry, University of Alberta, Edmonton, Canada; M. Romano, Texas Tech University Health Sciences Center, Lubbock; J. Romero, Creighton University, Omaha, Nebraska; P. Sanchez, University of Texas Southwestern Medical Center, Dallas; M. Shelton, Cook Children's Health Care, Ft Worth, Texas; J. Shigeoka, VA Medical Center, Salt Lake City, Utah; T.M. de Sierra, Hospital Infantil de Mexico, Mexico City; J. Sleasman, University of Florida, Gainesville; F. Smith, James Whitcomb Riley Hospital for Children, Indianapolis, Indiana; J. Smith, University of Texas Health Sciences Center, San Antonio; S. Sood, Schneider Children's Hospital, New Hyde Park, New York; L. Stanberry and D. Bernstein, University of Cincinnati Medical Center, Ohio; R. Steigbigel, State University of New York at Stony Brook; G. Storch, Washington University, St Louis, Missouri; T. Tan, Children's Memorial Hospital, Chicago, Illinois; J. Treanor, University of Rochester, New York; N. Tsarauhas, Cooper Hospital, Camden, New Jersey; R. Van Dyke, Tulane University Medical Center, New Orleans, Louisiana; L. Weiner, State University of New York Health Sciences Center, Syracuse; W. Williams, University of Colorado, Denver; and J. Zaia, City of Hope, Duarte, California.

	FOOTNOTES

Dr Gruber is currently affiliated with Wyeth Lederle Vaccines.

^a Members of the National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group are listed in "Acknowledgments."

Received for publication Sep 1, 2000; accepted Dec 11, 2000.

Reprint requests to (D.W.K.) University of Alabama at Birmingham, Division of Pediatric Infectious Diseases, 1600 Seventh Ave S, Suite 616, Birmingham, AL 35233. E-mail: dkimberlin{at}peds.uab.edu

	ABBREVIATIONS

HSV, herpes simplex virus; ID, intermediate-dose; HD, high-dose; SD, standard-dose; CNS, central nervous system; SEM, skin, eyes, or mouth; CASG, Collaborative Antiviral Study Group; CSF, cerebrospinal fluid; OR, odds ratio; AST, aspartate aminotransferase; ANC, absolute neutrophil count; CI, confidence interval.

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