Warning/Precautions Doctors advise against using famvir if you are allergic to any ingredient in it or if you have conditions like intolerance to glucose or lactase deficiency. Discuss your past/current medical history in detail with your doctor before beginning treatment with any new medication. If you are using any herbal supplements or over the counter medication, including vitamin pills, then mention it to your doctor. If you are expecting a child or are planning to have a child in the near future, then consult your doctor before using famvir to discuss any possible threats to the unborn baby. If you are a nursing mother and breast feed your baby, then too, seek consultation before using famvir as some drugs are excreted in the breast milk and may enter the baby.