COMPARISON OF THE IN-VITRO SUSCEPTIBILITY OF CLINICAL CYTOMEGALOVIRUSISOLATES TO CIDOFOVIR AND TO GANCICLOVIR

Cidofovir (CDF) or Vistid(R) is a monophosphate nucleoside analogue th at inhibits the DNA polymerase of herpes viruses including the cytomeg alovirus (CMV). CDF is active on GCV-resistant strains with a mutation on the phosphotransferase gene (UL97). However, DNA polymerase gene m utations that induce resistance to GCV are responsible for cross-resis tance to CDE Resistance phenotypes to GCV and CDF were determined for 57 CMV strains isolated from blood and urine samples. Sixteen strains were recovered after CDF therapy. Of the remaining 41 CDF-naive strain s, 34 were susceptible and seven resistant to GCV Fifty percent inhibi tory concentrations (IC50) for CDF were in the 0.2-2.6 CIM range for C DF-naive strains susceptible to GCV For GCV-resistant strains, IC50 va lues for CDF were less than or equal to 3 mu M for strains with a low level of resistance to GCV (GCV IC50 < 30 mu M) and greater than or eq ual to 6 mu M for three of the five strains with a high level of resis tance to GCV (GCV IC50 greater than or equal to 30 mu M).