Two hundred and forty-six patients with knee osteoarthritis and scheduled for an elective unilateral total knee arthroplasty were randomized to receive post-operative treatment with sequential intravenous parecoxib and oral celecoxib, or placebo. The primary outcome of interest was cumulative opioid consumption. Secondary outcomes of interest included the Knee Society Score (KSS), the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index, pain on a Visual Analog Scale (VAS) and the EQ-5D quality of life questionnaire. Follow up was performed up to 6 weeks post-operation, with adverse events recorded up to 12 weeks post-operation. Results revealed significantly lower cumulative morphine consumption at all time-points in the intervention group compared to the placebo group. Moreover, VAS pain scores, EQ-5D scores and KSS scores were significantly in favour of the intervention group compared to the placebo group. The incidence of adverse events was significantly lower in the intervention group compared to the placebo group.