Pharmacokinetics, pharmacodynamics, metabolism, toxicology and residues of phenylbutazone in humans and horses.

The presence of horse meat in food products destined for human consumption and labelled as beef has raised several concerns of public interest. This review deals solely with one aspect of these concerns; samples of equine tissue from horses destined for the human food chain have tested positive for the non-steroidal anti-inflammatory drug, phenylbutazone. The safety of some or all such foods for human consumers is a major concern, because it was shown many years ago that phenylbutazone therapy in humans can be associated with life threatening blood dyscrasias. As an initial basis for assessing the potential toxicity of foods containing phenylbutazone and its metabolites, this article reviews (1) the pharmacokinetic, pharmacodynamic, metabolic and toxicological profiles of phenylbutazone, with particular reference to horses and humans; (2) toxicity data in laboratory animals; (3) phenylbutazone residues in food producing species, and (4) as a preliminary assessment, the potential hazard associated with the consumption of horse meat containing phenylbutazone and its metabolites. Since phenylbutazone cannot be classified as a carcinogenic substance in humans, and noting that blood dyscrasias in humans are likely to be dose and treatment duration-dependent, the illegal and erratic presence of trace amount residues of phenylbutazone in horse meat is not a public health issue.