Disease-induced alterations in plasma drug-binding proteins and their influence on drug binding percentages in dogs

Disease-induced variations of plasma albumin (ALB) and alpha(1)-acid glycop rotein (AAG) levels were investigated in dogs. Lower ALE (sometimes >50% re duction) and higher,AAG (sometimes >10-fold increase) levels were observed in dogs with various diseases. Drug binding was determined at therapeutic c oncentrations using normal, low-ALE and high-AAG dog plasma. The binding pe rcentages of the ALE-binding drugs decreased in low-ALB plasma, resulting i n a large increase in unbound drug, particularly for naproxen (a 13-fold in crease).:The binding percentages of all AAG-binding drugs investigated in t his study increased in high-AAG plasma, resulting in a large decrease in un bound drug, particularly for quinidine (99% decrease). The fluctuation in t he unbound fraction of drugs could affect their efficacy or could cause sid e-effects. Veterinary clinicians should monitor the ALE and AAG levels in t he plasma of patients and correct dosage regimens according to these levels , where field conditions permit this, in order to ensure the proper usage o f drugs with high affinity for ALE or AAG.