Pharmacokinetics and dosage regimens of anti-inflammatory drugs

The term anti-inflammatory drug, in its broadest sense, encompasses a number of very diverse compounds, ranging from steroids to non-steroidal anti-inflammatory drugs (NSAIDs) and from disease modifying agents (used in the treatment of canine rheumatoid arthritis) to chondroprotective agents (used in the treatment of osteoarthrosis and traumatic arthritis in the horse). For many of these drugs (eg, chondroprotective and disease modifying agents) the mode of action is unknown and even with steroids and NSAIDs there is no universal agreement on mechanism of action. It is therefore in many cases impossible to link pharmacokinetic data to a drug's pharmacodynamics, for example to an effect on a specific biochemical marker. Some agents, including corticosteroids, may have indirect modes of action, so that the pharmacodynamic half-life can be much longer than (and not clearly related to) the pharmacokinetic half-life. In other cases, clinical benefits may only become apparent after several weeks or even months. It can therefore be difficult or impossible to use classical pharmacokinetic approaches to set dosing intervals and dose rates for clinical use. To some extent, the position is more straightforward with NSAIDs. However, even with these drugs simple approaches are not possible and this paper will review briefly some of the studies undertaken in our laboratory which have attempted to utilize NSAID kinetics to set dosage schedules for clinical use.