Glossary
Pharmacokinetics.
Direct answer
Pharmacokinetics describes the route of a substance through the body: absorption, distribution into tissues, transformation in the liver and other organs, and excretion. Pharmacokinetics answers what concentration is present, where and when. What the substance does once it is there belongs to pharmacodynamics instead.
Four steps organise the field: absorption, distribution, metabolism and excretion. The commonest error is to infer effect directly from the amount given. Between the two sit the route of entry, binding to blood proteins, perfusion of the target tissue and the half-life. Questions of amount and use belong with a veterinary surgeon.
Two features of the horse complicate borrowing data from other species. The hindgut houses a very large microbial community able to modify substances, and enzyme equipment and excretion routes differ from the human pattern. Regulated detection times in equestrian sport add a further reason why equine pharmacokinetic data matter.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.