Parecoxib, celecoxib and paracetamol for pain management following caesarean delivery

All women will receive patient-controlled epidural analgesia (PCEA) with pethidine (20 mg bolus, 15 minute lock-out, no background) and either: 1) placebo (intravenous normal saline 2 ml & normal saline 200 ml intra-operatively; oral placebo capsules - 2 capsules at 6 and 18 hours postoperatively & 4 capsules at 12 hours postoperatively) 2) cyclo-oxygenase 2 enzyme (COX-2) inhibitors (intravenous parecoxib 40 mg in 2 ml normal saline and placebo [normal saline 200 ml] intra-operatively; post-operatively, oral celecoxib 400 mg [2 x 200 mg capsules] at 12 hours postoperatively and 2 placebo capsules PO at 6, 12 and 18 hours) 3) intravenous paracetamol 2 g in 200 ml normal saline and intravenous normal saline 2 ml intra-operatively; post-operatively, oral paracetamol 1 g [2 x 500 mg capsules] at 6, 12 and 18 hours and 2 additional placebo capsules at 12 hours 4) COX-2 inhibitors and paracetamol in combination (intravenous parecoxib 40 mg in 2 ml normal saline and paracetamol 2 g in 200 ml normal saline intra-operatively; post-operatively, oral paracetamol 1 g [2 x 500 mg capsules] at 6, 12 and 18 hours and oral celecoxib 400 mg [2 x 200 mg capsules] at 12 hours) Intra-operative drugs will be given after delivery. All women will have access to rescue analgesia - immediate release oral tramadol 100 mg 2 hourly (maximum 600 mg in 24 hours). The placebo capsules are cornstarch in a gelatin capsule. The paracetamol 2 g in 200 ml normal saline or the placebo equivalent of 200 ml normal saline will be infused over 15 minutes. The parecoxib 40 mg in 2 ml normal saline or the placebo equivalent of 2 ml normal saline will be given as a bolus.