title: Is combination antiviral therapy for CMV superior to monotherapy?
abstract: BACKGROUND
  Many clinicians are under the impression that the combination of ganciclovir (GCV) and foscarnet is synergistic versus cytomegalovirus (CMV) and/or that combination therapy might prevent the emergence of resistance to one or both antivirals. The combination is frequently used when resistance to either drug is suspected.
  
  
  OBJECTIVE
  To review in vitro and clinical data regarding the activity of ganciclovir plus foscarnet and evidence of synergy between the two drugs.
  
  
  METHODS
  We reviewed two in vitro studies of synergy between ganciclovir and foscarnet followed by reviewing all clinical studies utilizing series of patients.
  
  
  RESULTS
  The combination of ganciclovir and foscarnet was synergistic against three clinical isolates, the Towne strain and one laboratory derived strain moderately resistant to GCV but synergy was not demonstrated against laboratory derived strains highly resistant to GCV or foscarnet. AD169, susceptible to both drugs, was not inhibited synergistically by the combination in one study but was in the second study. In the only carefully controlled in vivo study of combination versus monotherapy for GCV susceptible viremia superiority of the combination was not demonstrated. In treating clinically resistant CMV retinitis, the combination was superior to continued or alternative monotherapy.
  
  
  CONCLUSIONS
  There is suggestive but inconclusive evidence of in vitro synergy for the combination of GCV and foscarnet versus CMV with very limited data versus GCV resistant virus. The in vivo data for synergy is even less convincing. Additional in vitro and in vivo data is needed, especially to prevent or treat CMV resistance.
authors.affiliation: UCSF Mount Zion Medical Center, University of California-San Francisco, 1600 Divisadero Street, Box 1629, San Francisco, CA 94115, USA. lawrence.drew@clinlab.ucsfmedctr.org
authors.forename: W Lawrence
authors.initials: WL
authors.lastname: Drew
mesh_terms: D000998:Antiviral Agents / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D003587:Cytomegalovirus / Q000187:drug effects; D003586:Cytomegalovirus Infections / Q000188:drug therapy* / Q000821:virology; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D017245:Foscarnet / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D015774:Ganciclovir / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D008826:Microbial Sensitivity Tests; D016032:Randomized Controlled Trials as Topic; D016896:Treatment Outcome
chemical_list: D000998:Antiviral Agents; D017245:Foscarnet; D015774:Ganciclovir