Famciclovir is a medication commonly used to treat infections caused by viruses, such as herpes simplex and varicella-zoster [1][2]. While famciclovir is generally well-tolerated, there are potential side effects that may restrict its administration.

According to the National Center for Biotechnology Information (NCBI) [2], common side effects of famciclovir include:

* Nausea
* Headache
* Fatigue

Less common side effects include:

* Diarrhea
* Rash
* Vomiting
* Dizziness

Rare but serious side effects include:

* Allergic reactions
* Anemia
* Seizures
* Changes in mental status
* Kidney failure

It is essential to note that the likelihood of experiencing these side effects varies from person to person, and not everyone will experience them [2]. However, if any of these side effects occur, it is crucial to seek medical attention promptly.

Moreover, MedlinePlus states that people with certain medical conditions, such as kidney disease or immune system disorders, may need to use famciclovir with caution [1]. In addition, famciclovir may interact with other medications, such as probenecid and cimetidine, which may affect its effectiveness or increase the risk of side effects [1].

In summary, the potential side effects of famciclovir may restrict its administration, particularly in individuals with certain medical conditions or those taking specific medications. Therefore, it is essential to consult with a healthcare provider before starting famciclovir to ensure its safe and effective use.

Sources:
[1] MedlinePlus. (2021). Famciclovir. Retrieved from <https://medlineplus.gov/druginfo/meds/a694038.html>
[2] National Center for Biotechnology Information. (2021). Famciclovir. Retrieved from <https://www.ncbi.nlm.nih.gov/books/NBK557563/>
[3] DrugPatentWatch. (n.d.). Famciclovir. Retrieved from <https://www.drugpatentwatch.com/p/tradename/FAMCICLOVIR>