Summary of HSV-1 susceptibility to acyclovir and penciclovir by antiviral use and medical historya

ClinicalACV (Vero cells)PCV (MRC-5 cells)
No. of subjectsMedian IC50 (μg/ml)bPcNo. of subjectsMedian IC50 (μg/ml)bPc
Previous use of an antiviral agent (ACV, FCV, PCV, VCV)
    Used an antiviral agent3310.410.2113330.260.649
    Never used an antiviral agent6620.446620.26
Current antiviral agent usage (oral ACV, FCV, VCV)
    Using an antiviral agent490.310.025490.240.488
    Not using an antiviral agent9430.439450.26
Immune status
    Potential immunocompromised370.390.274380.250.377
    No immunocompromise9590.429600.26
No. of RHL episodes in past 12 mo
Duration of history of RHL
    <16 yr3320.390.1153330.260.804
    ≥16 yr6510.446520.26
Avg duration of an RHL episode
    <6 days2650.450.2232660.270.644
    ≥6 days7350.417360.26
  • a No meaningful comparisons of the potency of acyclovir and penciclovir can be made because the isolates were tested in different cell lines. Abbreviations: ACV, acyclovir; FCV, famciclovir; PCV, penciclovir; VCV, valacyclovir.

  • b The mean ± SD IC50 of acyclovir for all isolates was 0.53 ± 0.39 μg/ml; that of penciclovir was 0.28 ± 0.11 μg/ml. For sensitive reference strain SC16, the mean ± SD IC50 of acyclovir in all assays was 0.57 ± 0.34 μg/ml; that of penciclovir was 0.20 ± 0.17 μg/ml. For resistant HSV-1 reference strain DM21, the mean ± SD IC50s of acyclovir ranged from 14.35 to >30 μg/ml; the mean ± SD IC50s of penciclovir for HSV-1 DM21 ranged from 2.26 to >30 μg/ml.

  • c Medians within each subgroup were compared by the Wilcoxon rank sum test with the t-test approximation.

  • d Based on subjects' reported medication and medical histories.