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 glycoprotein (AAG) levels were investigated in dogs. Lower ALE (sometimes >50% reduction) and higher,AAG (sometimes >10-fold increase) levels were observed in dogs with various diseases. Drug binding was determined at therapeutic concentrations using normal, low-ALE and high-AAG dog plasma. The binding percentages of the ALE-binding drugs decreased in low-ALB plasma, resulting in a large increase in unbound drug, particularly for naproxen (a 13-fold increase).:The binding percentages of all AAG-binding drugs investigated in this study increased in high-AAG plasma, resulting in a large decrease in unbound drug, particularly for quinidine (99% decrease). The fluctuation in the unbound fraction of drugs could affect their efficacy or could cause side-effects. Veterinary clinicians should monitor the ALE and AAG levels in the plasma of patients and correct dosage regimens according to these levels, where field conditions permit this, in order to ensure the proper usage of drugs with high affinity for ALE or AAG.