Based on the available information, there are no specific antiviral drugs that have been reported to have harmful interactions when combined with famciclovir. However, it is important to note that combining antiviral drugs should be done under the supervision of a healthcare professional, as there is a risk of increased side effects and decreased effectiveness of both drugs due to overlapping toxicities [2].

Famciclovir is an antiviral drug commonly used to treat herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections [3]. The CDC treatment guidelines for herpes recommend the use of antiviral drugs such as acyclovir, valacyclovir, and famciclovir for the treatment of genital herpes [2].

A study published in the National Center for Biotechnology Information (NCBI) found that combining famciclovir with other antiviral drugs such as acyclovir and ganciclovir did not show any significant pharmacokinetic interactions [1]. However, this does not mean that there are no potential drug-drug interactions when combining famciclovir with other antiviral drugs, and it is important to consult a healthcare professional before combining any medications.

In summary, while there are no specific antiviral drugs that should not be combined with famciclovir, it is important to consult a healthcare professional before combining any medications due to the potential for increased side effects and decreased effectiveness.

Sources:

* <https://www.drugpatentwatch.com/p/tradename/FAMCICLOVIR>
* <https://www.cdc.gov/std/treatment-guidelines/herpes.htm>
* <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7728158/>