Found this study in reguard to preventing CMV in organ transplant. It seems that theres not much difference between 450mg versus 900mg, the higher dose seems to be related to more side effects. These dosages maybe different to treating active infection i suppose, but the lower dosage if used in cfs/me make valcyte more affordable to try, maybe with another antiviral?? http://cid.oxfordjournals.org/content/52/3/313.abstract cheers!!!