Renal mesangial cells were used in the cell viability assay. Cells were seeded 12–16 h before drug treatment at densities of 10,000 cells per well. Six drug dilutions were prepared as follows: 1,000, 100, 10, 1, 0.1 and 0.01 µmol/l. The growth medium without drugs was set as the control group. Each dilution group was tested in five duplicates. The drug solution was added into the wells and cells were cultured at 37°C in 5% CO₂. A total of 24 h later, the drug solution was removed and each well was fed with fresh medium containing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and incubated for another 4 h. The medium and MTT were removed and the MTT-formazan crystals were dissolved by dimethyl sulfoxide. The optical values were tested at 570 nm. Data were analyzed by SPSS version 18.0 (SPSS, Inc., Chicago, IL, USA) and Graphpad prism 5.0 software (GraphPad Software, Inc., La Jolla, CA, USA).

A total of 944 hospitalized patients who were randomly selected from a third-grade class-A teaching hospital (the Second Affiliated Hospital of Nanjing Medical University, of Nanjing Medical University, Nanjing, China) between January 2009 and December 2012 were included in the cohort study. The inclusion criteria were patients who needed to receive conventional treatment (2.0 g every 12 h) of fourth-generation cephalosporin (cefepime or cefpirome) according to clinical diagnosis, additionally with an originally normal renal function and creatinine clearance rate. Excluded criteria included chronic renal insufficiency, nephrotic syndrome, renal transplantation, previous use of aminoglycoside antibiotic drugs, combined-use of antimicrobial agents and previous treatment of nephrotoxic drugs. Patients were divided by drug treatment and among each drug group, patients were divided into two age groups: <65 and ≥65 years. The clinical characteristics of patients included are described in Table I.

The renal function of patients was tested by examining the SCr level before, and on days 3 and 7 during the therapy. Following this, the average levels of SCr in each group were calculated; the incidence of SCr >445 µmol/l, as an indicator for potential renal failure, was recorded.

P<0.05 was considered to indicate a statistically significant difference.

As depicted in Table II and Fig. 1, cefepime and cefpirome showed significant inhibition on cell activity compared to the control group and the inhibition rate was dependent on the drug concentration. In each dilution group, cefpirome exhibited a higher inhibition on cell viability than cefepime, as shown in Table II and Fig. 2. Additionally, the half maximal inhibitory concentration (IC₅₀) of the drugs on renal mesangial cells for 24 h was 143.5 and 7.702 µmol/l for cefepime and cefpirome, respectively.

As shown in Table III, treatment of cefepime resulted in a greater increase of SCr in the two age groups compared to cefpirome. In patients aged <65 years, cefepime rose from an average SCr level of 67±7.4 to 83±11.1 µmol/l on day 3 and 87±10.3 µmol/l on day 7, while cefpirome augmented an average SCr level from 65±8.7 to 95±10.9 µmol/l on day 3 and 98±14.2 µmol/l on day 7. On day 3, none of the patients suffered from SCr >445 µmol/l in the cefepime group, but one patient suffered in the cefpirome group (incidence, 0.6%). On day 7, one case in the cefepime group (incidence, 0.6%) and two additional cases in the cefpirome group (incidence, 1.9%) exhibited SCr >445 µmol/l, as shown in Table IV.

In patients aged ≥65 years, a higher increase of SCr was observed for the two drugs. In the cefepime group, the average SCr level was 91±11.7 µmol/l on day 3 and 102±11.8 µmol/l on day 7, while for the cefepime group the level was 130±12.4 and 155±13.1 µmol/l on days 3 and 7, respectively. Among the ≥65 age group, the incidence of SCr >445 µmol/l increased, which was 0.3% (one case) on day 3 and 0.7% (two cases) on day 7 for the cefepime group, and 1.3% (four cases) on day 3 and 3.2% (10 cases) on day 7 for the cefpirome group, as depicted in Tables III and IV.