NSAIDs and cox inhibitors NSAIDs inhibit the enzyme cyclo oxygenase which catalyses the conversion of arachidonic acid to prostaglandins. This action accounts for the potent anti-inflammatory and analgesic effects of these drugs and for their relatively common adverse effects. The NSAIDs belong to three different chemical families. so some patients who are intolerant of one drug may be able to take another NSAID from a different family. The anti-prostaglandin side-effects, however, are common to all drugs in this class. The NSAIDs most widely used in the UK for acute postoperative pain are ibuprofen (typically 400 mg three to four times daily) and diclofenac (50 mg three times daily). Diclofenac is also available in suppository form and as an injection. Intramuscular diclofenac has been associated with a high incidence of sterile abscess and persistent pain and is best avoided. Recently. a new formulation of diclofenac licensed for intravenous use was released. The use of cyclodextrin as a solubilizing agent allows pain-free bolus administration without the need for dilution and buffering which is required for the existing product. NSAIDs cause a number of adverse effects as a consequence of their action on cyclo-oxygenase (see Box 1). There is inhibition of platelet aggregation resulting in a prolongation of bleeding time. NSAIDs per se do not. however, affect the prothrombin time or the activated partial thromboplastin time. Some studies have shown increased blood loss, greater need for transfusion and higher risk of haematoma formation when NSAIDs have been used. This effect on platelet function may complicate the use of other anti- coagulants such as heparin and warfarin. Furthermore, NSAIDs may displace warfarin bound to plasma proteins further inhibiting coagulation. For these reasons NSAIDS should be avoided or used with caution in patients receiving other anticoagulants.