title: [Resistance studies: when are they indicated?].
abstract: Cytomegalovirus (CMV) resistance to antiviral drugs is an emerging problem and is due to selection of mutations in the viral genome. Although ganciclovir resistance is the most common and widely studied, there is resistance to all antiviral agents. Risk factors for the development of resistance are the absence of preexisting immunity to CMV, lung and pancreas transplantation, high viral loads, intense concomitant immunosuppressive therapy and prolonged exposure to ganciclovir or suboptimal levels of this drug. Antiviral resistance should be suspected when, despite adequate treatment exposure for 2 weeks, an increase in viral load, or persistence or clinical progression of CMV disease are detected. However, failure to respond cannot always be attributed to antiviral resistance nor does resistance always lead to poor clinical outcome. When resistance is suspected, phenotypic and genotypic confirmation is required. The most common mutations are those in the UL97 gene, which confers ganciclovir resistance. However, foscarnet and cidofovir can be used. The UL54 mutation is not uncommon, whether alone or in combination with UL97 mutations. The combination of UL54 and UL97 mutations is associated with high-grade and multiple resistance. Early detection of resistance is essential to prevent unfavorable outcome and the development of multi-drug resistance. In patients with a slow response to treatment and without mutations associated with resistance, plasma ganciclovir levels and specific CMV immunity should be investigated.
authors.affiliation: Servicio de Microbiología, Hospital Clínic de Barcelona, Barcelona, España. mmarcos@clinic.ub.es
authors.forename: M
authors.initials: M
authors.lastname: Angeles Marcos
mesh_terms: D000998:Antiviral Agents / Q000627:therapeutic use*; D003586:Cytomegalovirus Infections / Q000188:drug therapy*; D024882:Drug Resistance, Viral; D006801:Humans
chemical_list: D000998:Antiviral Agents