Pharmacokinetics of ceftazidime after intravenous and intramuscular administration to domestic cats

The pharmacokinetic properties of ceftazidime, a third generation cephalosporin, were investigated in five cats after single intravenous (IV) and intramuscular (IM) administration at a dose rate of 30 mg/kg. Minimum inhibitory concentrations (MICs) of ceftazidime for some Gram-negative (Escherichia coli, n = 11) and Gram-positive (Staphylococcus spp., n = 10) strains isolated from clinical cases were determined. An efficacy predictor, measured as the time over which the active drug exceeds the bacteria minimum inhibitory concentration (T > MIC), was calculated. Serum ceftazidime disposition was best fitted by a bi-compartmental and a mono-compartmental open model with first-order elimination after IV and IM dosing, respectively. IV administration, distribution was rapid (t1/2(d) 0.04 ± 0.03 h), with an area under the ceftazidime serum concentration:time curve (AUC(0–∞)) of 173.14 ± 48.69 μg h/mL and a volume of distribution (V(d(ss))) of 0.18 ± 0.04 L/kg. Furthermore, elimination was rapid with a plasma clearance of 0.19 ± 0.08 L/h kg and a t1/2 of 0.77 ± 0.06 h. Peak serum concentration (Cmax), Tmax, AUC(0–∞) and bioavailability for the IM administration were 89.42 ± 12.15 μg/mL, 0.48 ± 0.49 h, 192.68 ± 65.28 μg h/mL and 82.47 ± 14.37%, respectively. Ceftazidime MIC for E. coli ranged from 0.0625 to 32 μg/mL and for Staphylococcus spp. from 1 to 64 μg/mL. T > MIC was in the range 35–52% (IV) and 48–72% (IM) of the recommended dosing interval (8–12 h) for bacteria with a MIC90 ⩽4 μg/mL.