Pilot study of side effects and serum and urine concentrations of amoxicillin-clavulanic acid in azotemic and non-azotemic cats.

Objectives The aims of this study were to determine the side effect frequency and serum and urine drug concentrations of amoxicillin-lavulanic acid in cats with and without azotemic chronic kidney disease (azCKD). Methods Owners whose cats had been prescribed amoxicillin-clavulanic acid completed a survey regarding the occurrence and type of side effects, and whether treatment was altered as a result. Cats were defined as azCKD (serum creatinine concentration >2.0 mg/dl, urine specific gravity [USG] <1.035 with a clinical diagnosis of CKD) and without azCKD (serum creatinine concentration <2.0 mg/dl). Data were assessed with Fisher's exact test. Serum and urine samples were obtained from client-owned cats with azCKD (n = 6) and without azCKD (n = 6, serum creatinine concentration <1.8 mg/dl, USG >1.035) that were receiving amoxicillin-clavulanic acid. Amoxicillin and clavulanic acid were measured with liquid chromatography coupled to tandem mass spectrometry and compared between groups with a Mann-Whitney test. Correlation between serum creatinine and drug concentrations in urine and serum was determined using Spearman's rank test. Results Sixty-one surveys were returned (11 azCKD cats and 50 without azCKD cats). No significant difference in the presence of side effects or type of side effects was seen between groups; however, significantly more azCKD cats had more than one side effect (P = 0.02). More owners of azCKD cats reported that an alteration in treatment plan was necessitated by side effects (55% vs 12%; P = 0.008). Urine amoxicillin was significantly lower in cats with azCKD (P = 0.01) and serum amoxicillin trended toward significance (P = 0.07). Serum amoxicillin concentration was positively correlated with serum creatinine (P = 0.02; r = 0.62) and urine amoxicillin concentration was negatively correlated with serum creatinine (P = 0.01; r = -0.65). Conclusions and relevance The data suggest that cats with azCKD have altered pharmacokinetics of amoxicillin, which may contribute to an increased incidence of multiple side effects.