Ninety patients, undergoing breast surgery, were included in one of the three groups (Ibuprofen, Hydromorphone, Ibuprofen+Hydromorphone groups). Positive analgesic efficacy was defined as a numeric rating scale (NRS) ≤3 on a 0-10 NRS, 30 min after the drug administration. Drug was administered by the Dixon and Mood up-and-down method. Starting doses were ibuprofen 50 mg, hydromorphone 0.25 mg, or ibuprofen 25 mg + hydromorphone 0.125 mg. The maximum doses were ibuprofen 800 mg, hydromorphone 2 mg, or ibuprofen 400 mg + hydromorphone 1 mg. Combination index (CI) (additive: 0.9-1.1, synergism: \<0.9, antagonism: \>1.1), dose reduction index (DRI, a measure of how much the dose of each drug in a combination can be reduced), and isobologram were used to define the nature of their interaction.
