Antibiotics (AB) are sometimes used in patients taking anti-inflammatory drugs (AID) (steroidal and non steroidal anti-inflammatory drugs). At the present time, the usefulness of AID in bacterial infections has been established in a limited number of clinical situations. AID are able to modify the kinetics of AB through different mechanisms which are illustrated by results obtained with cephalosporins and phenylbutazone or diclofenac. In some conditions, these modifications might have consequences on in vivo effect of AB. Conversely, some AB are able to alter metabolism and/or kinetics of some steroids. Interactions of AI on AB toxicity have also been investigated on kidney and central nervous system. AB/AI kinetic interactions have to be investigated for a better understanding of the mechanisms through which AI improve the evolution of an infectious process.