In an article entitled “Clinical Potential of the Acyclic Nucleoside Phoshonates Cidofovir, Adefovir and Tenofovir in Treatment of DNA Virus and Retrovirus Infections” (Clinical Microbiology Reviews, 2003) Erik De Clercq found that both cidofovir and adefovir dipivoxil work well for a wide range of viruses including HHV-6 and were superior to ganciclovir for viruses such as CMV.

Antiviral activity spectrum of the acyclic nucleoside phosphonates

Virus Cidofovir Adefovirdipivoxil
Polyomavirus Yes
Pappillomavirus Yes
Adenovirus Yes
HSV-1 Yes Yes
HSV-2 Yes Yes
VZV Yes Yes
CMV Yes Yes
EBV Yes Yes
HHV-6 Yes Yes
HHV-7 Yes Yes
HHV-8 Yes Yes
Variola Yes
Cowpox Yes
Monkeypox Yes
Camelpox Yes
Vaccinia Yes
Orf Yes
Hepatitis B Yes Yes
HIV-1 Yes
HIV-2 Yes

*From De Clercq, Clinical Microbiology Reviews, 2003

Although adefovir (Hepsera), a cousin of cidofovir, showed efficacy in vitro and is available in an oral form for hepatitis B, the dose is considered too small to pass the blood brain barrier in sufficient quantities. Larger doses showed kidney toxicity.

In a study done at the University of Alabama, Long et al found that the selectivity index was higher for cidofovir than either ganciclovir or foscarnet for HHV-6A. The following data was presented in their article entitled “Determination of antiviral efficacy against lymphotropic herpesviruses utilizing flow cytometry” in Antiviral Research (2003):

EC50 (µg/ml) In HSB-2 cells In Sup T1 cells
cidofovir 4.6 mcg/µl 2.0 mcg/µl
foscarnet 9.5 mcg/µl 6.3 mcg/µl
ganciclovir 10.6. mcg/µl 7.6 mcg/µl

See Experimental & Alternative Treatments
Read about antiviral use in transplant patients with HHV-6 encephalitis

See the Foundation’s interview with Drs. Eric De Clerq and Lieve Naessen’s of the Rega Institute on epilepsy and antiviral treatment

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