Diclofenac sodium (Voltarol): drug interactions and special studies

Diclofenac (Voltarol) has no effect on carbohydrate metabolism, insulin levels or tolbutamide metabolism, nor does it enhance the effect of tolbutamide, biguanide or glibenclamide. Although it produces minimal increases in prothrombin and partial thromboplastin times in healthy volunteers, it does not significantly affect the individual clotting factors, nor does it, in patients, enhance the effect of acenocoumarol or phenprocoumon. Like many other other non-steroidal anti-inflammatory drugs, it increases platelet aggregation time. There is a pharmacokinetic interaction between aspirin and diclofenac. Two independent studies have shown that aspirin markedly reduces the bioavailability of diclofenac, as measured by "area under the curve". Furthermore, patients exhibiting aspirin sensitivity as bronchospasm are likely to react to diclofenac in the same manner. Finally, diclofenac, as tested using excretion of 51Cr labelled red cells, induces minimal gastrointestinal blood loss, significantly less so than aspirin or naproxen.