*Purpose: Famciclovir is recommended for herpes simplex virus (HSV) and varicella-zoster virus (VZV) prophylaxis in cytomegalovirus (CMV) low risk (both donor and recipient CMV seronegative) solid organ transplant (SOT) recipients in current guidelines, however there is no data evaluating its use in SOT recipients. At our institution, we use famciclovir dosed at 500 mg daily for 3 months as a convenient option, with the lowest pill burden, for HSV/VZV prophylaxis. We aimed to evaluate the efficacy and safety of once daily famciclovir for antiviral prophylaxis, in addition to conducting a multicenter provider survey on antiviral prophylaxis in CMV low risk SOT recipients.

*Methods: Two-part analysis was done, consisting of a retrospective chart review of kidney transplant recipients discharged on famciclovir between April 2, 2016 and August 31, 2018 and a national provider survey. The primary outcome of the chart review was the incidence of HSV, VZV or CMV infection at 12 months post-transplant. Secondary outcomes included immunosuppression doses and levels, famciclovir dose, hematology cell counts, and renal function at predetermined time points post-transplant. Rates of acute rejection, graft loss/failure, and incidence of famciclovir premature discontinuation were also collected.

*Results: Of the 78 patients included in our retrospective chart review, one patient (1.3%) developed a VZV infection at 12 months post-transplant after completing prophylaxis (Table 1). One patient (1.3%) required premature discontinuation of famciclovir due to concern for acute interstitial nephritis. There was a low incidence of additional safety endpoints including graft loss, rejection, death with functioning graft and filgrastim administration. Providers from forty-five transplant centers within the United States responded to the survey. Across all organs, acyclovir 400 mg twice daily was utilized by most respondents (70.4%) for a duration of 3 months (68.8%). No respondents reported use of famciclovir at their institution (Table 2).

*Conclusions: Among our patients receiving the novel regimen of famciclovir 500mg once daily for CMV low risk antiviral prophylaxis, there were no documented cases of HSV/VZV/CMV infection while on prophylaxis. Nationwide, the most common antiviral prophylaxis used in CMV low risk SOT recipients is acyclovir 400 mg twice daily. Once daily famciclovir may provide an effective and convenient once daily dosing regimen for antiviral prophylaxis in CMV low risk SOT recipients.

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