Vaptan Tolvaptan Rifampicin
MajorRifampicin (called rifampin in the leaflet) is a CYP 3A inducer, and the advice is to avoid taking it together with tolvaptan. It can lower the level of tolvaptan in the blood, so tolvaptan may work less well.
These medicines can affect each other in a serious way. Do not start taking them together unless your doctor has said it is OK. If you already take both, do not stop either one on your own: speak to your doctor or pharmacist soon.