Various strains of cytomegalovirus (CMV) may become resistant to antiviral drugs during prolonged antiviral therapy.


When to suspect emergence of antiviral resistance:

(1) persistent or increasing plasma viral loads and/or overt CMV disease during therapy with appropriate drugs given appropriately

(2) accumulation of multiple viral mutations associated with drug resistance over time


Some patients infected with resistant CMV may be asymptomatic, so genotypic analysis the most sensitive method to detect antiviral resistance.


Factors associated with appearance of antiviral resistance:

(1) immunosuppression

(1a) AIDS without HAART

(1b) transplant recipients, especially if negative recipient receives a transplant from a positive donor

(2) exposure to patients with resistant strains

(3) prolonged exposure to antiviral agents


Treatment of a patient with CMV showing antiviral resistance may include:

(1) modifying the current regimens, typically with an increase in dose

(2) switch to a different drug

(3) combination dosing with 2 or more antiviral agents

(4) use of an experimental drug

(5) trying to improve host defenses by modifying the underlying disease


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