The nephrotoxic potential of gentamicin in the cat: enzymuria and alterations in urine concentrating capability.

This study investigated the potential for nephrotoxicity of gentamicin in cats by measuring marker enzyme concentrations, [Na], [K], osmolality, and pH of the urine, and blood urea nitrogen (BUN) levels. Gentamicin was administered i.m. at 4.4 mg/kg once daily (s.i.d.) or twice daily (b.i.d.) for 7 days. Concentrations of lactic dehydrogenase (LDH), lysozyme (LZM), alkaline phosphatase (AP), and glutamate dehydrogenase (GD) were measured as total 24-h excretions. The s.i.d. regimen produced only a slight increase in LDH excretion after 5 days, whereas the b.i.d. regimen caused an increase in the excretion of all enzymes. The greatest elevations were observed for LZM and LDH. Of the enzymes studied, these appeared to be the most appropriate to monitor for potential nephrotoxicity, except that urinary concentrations did not correlate well with duration of gentamicin administration. Only slight elevations in BUN were observed for either regimen. Single daily administration increased urine osmolality slightly, but b.i.d. treatment caused a marked and immediate decrease in urine osmolality, [Na], and total Na excretion. Urinary [K] was also depressed, as was total K excretion after 6 days. Urine pH was not substantially affected. This study showed that the recommended daily dose of 4.4 mg/kg produced little if any evidence of nephrotoxicity as indicated by the parameters measured. Twice daily dosing, however, produced elevations in urine enzyme concentrations, and markedly decreased urine osmolality and Na and K excretion. Compared to other species studied, the cat appears particularly sensitive to urine concentrating alterations resulting from repeated gentamicin administration.