I was just put on monodox but was already on toviaz (fesoterodine). Do I take both? Is that safe?

They R fine together. Monodox is an antibiotic famously known as doxycycline. Toviaz (fesoterodine) is a long-termedication for overactive bladder (bladder spasm) and has no known interaction with monodox. I assume u are given Monodox for some type of infections, possibly 2x/day for about 10-14 days? So, i would take both as prescribed. If you experience significant side effects, consult doc. Good luck.