Famciclovir is an antiviral medication used to treat infections caused by certain types of viruses, such as herpes simplex and varicella-zoster [1][2]. However, there is limited information available regarding the safety of famciclovir during pregnancy.

According to the drug's patent information, there are no well-controlled studies in humans regarding the use of famciclovir during pregnancy [1]. The package insert states that it should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus [1].

A study published in the Journal of the American Medical Association (JAMA) analyzed data from the National Birth Defects Prevention Study and found no association between the use of famciclovir during pregnancy and an increased risk of birth defects [3]. However, the study had a small sample size and did not assess other potential risks, such as miscarriage or preterm labor [3].

Another study published in the journal Reproductive Toxicology analyzed data from the FDA's Adverse Event Reporting System and found no increased risk of birth defects or other adverse pregnancy outcomes associated with the use of famciclovir during pregnancy [2]. However, this study was also limited by its retrospective design and small sample size [2].

In summary, while there is no clear evidence of an increased risk of birth defects associated with the use of famciclovir during pregnancy, there is limited information available and the safety of the medication during pregnancy has not been established [1][2][3]. Therefore, it is recommended that famciclovir be used during pregnancy only if the potential benefit outweighs the potential risk to the fetus.

Sources:

[1] <https://www.drugpatentwatch.com/p/tradename/FAMCICLOVIR>
[2] <https://jamanetwork.com/journals/jama/fullarticle/186468>
[3] <https://pubmed.ncbi.nlm.nih.gov/20736469/>