Valacyclovir can harm your kidneys. This effect is increased when you also use certain other medicines, including: antivirals, chemotherapy, injected antibiotics, medicine for bowel disorders, medicine for high blood pressure, medicine to prevent organ transplant rejection, injectable osteoporosis medication, and some pain or arthritis medicines (including Advil, Motrin, and Aleve).
Other drugs may interact with valacyclovir, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.
 Valacyclovir drug interactions (more detail)
