BID: bis in die, twice a day; TID: ter in die: three times a day.

The appropriate dosing regimen for a drug depends on exposure-response relationships (see dose finding and dose fractionation study) and is based on in vitro, in vivo, and clinical evidence. Depending on the drug class and its pharmacokinetic and pharmacodynamic properties, different dosing regimens may be optimal, including once a day (omne in die, OD), twice a day (bis in die, BID) or three times a day (ter in die, TID).