Cyst infection in autosomal dominant polycystic kidney disease: penetration of meropenem into infected cysts

We enrolled patients in the study according to the following criteria. All ADPKD patients receiving MEPM for cyst infection who underwent drainage of infected cysts at Toranomon Hospital from August 2013 to January 2014 were screened and patients without confirmation of definite cyst infection by detection of neutrophils in cyst fluid were excluded. We adopted the criteria for definite cyst infection of Sallee et al. (neutrophils in cyst fluid) [3] to ensure that only patients with definite infection were enrolled. However, our classification of hepatic cyst infection or renal cyst infection relied on the fact that the drained cysts contained neutrophils on cyst fluid analysis, and it did not ensure that the other organ had no concomitant infection. Therefore, there might be overlap between hepatic cyst infection, renal cyst infection, and infection in other organs. All 10 patients fitting these criteria gave written consent after being fully informed about this study.

The symptoms of cyst infection were assessed from the clinical records, as were the laboratory findings using data obtained from the earliest tests performed after the onset of symptoms. The maximum body temperature (BT), the presence or absence of abdominal pain/back pain or tenderness and pyuria/haematuria, and the maximum white blood cell (WBC) count and serum C-reactive protein (CRP) level within one week after the onset of infection were recorded. The maximum BT, WBC count, and blood culture results were investigated before initiation of antibiotic therapy. These clinical data are presented in Table 1 and past medical history of each patient is presented in Additional file 1 (Past medical history of each patient).

Abdominal MRI was performed in all patients with suspected cyst infection in this study because none of them had contraindications to MRI such as a cardiac pacemaker. Abdominal computed tomography (CT) was performed in the patients with suspected cyst haemorrhage. When MRI was done, transverse and sagittal T1-weighted images (T1WI), T2-weighted images (T2WI), and diffusion–weighted images (DWI) were usually obtained, as reported previously [6]. None of the patients underwent gadolinium-enhanced MRI because 9 out of 10 patients had renal dysfunction. CT was performed as reported previously [6], and was usually done without enhancement because plain scans are adequate for identifying cyst haemorrhage and most of the patients had renal dysfunction. We did not perform 18-FDG PET/CT in any of the patients enrolled in this study.

Our hospital policy was to only employ carbapenems in patients with cyst infection that was refractory to other antibiotics or patients with specific risk factors such as leukopenia, and physicians required submit reports to the infection control committee of Toranomon Hospital for using carbapenems. In all of the enrolled patients, the cyst infection had shown resistance to other antibiotics and treatment with MEPM was required. For administration, MEPM (0.5 g) was dissolved in 50 mL of saline and infused intravenously over 30 min. In each patient, we adjusted the MEPM dosage for renal function based on the Sanford Guide to Antimicrobial Therapy (2013). All patients on dialysis received the same dose of MEPM (0.5 g once a day) and the dose was not adjusted for body weight. The information about the antibiotics administered before MEPM and the duration of prior therapy, as well as the duration of MEPM administration in each patient are presented in the Additional file 2 (Antibiotics used in each patient).

Percutaneous aspiration of an infected cyst was usually considered if a patient’s fever persisted for 1–2 weeks despite appropriate antimicrobial therapy as it is generally recommended [7]. Cyst drainage was performed on a non-dialysis day in all patients receiving hemodialysis. Infected cysts were detected according to our diagnostic criteria [6]. After the infected cyst was identified by abdominal MRI, aspiration was done under ultrasound guidance. A 10.2 Fr pigtail catheter with side holes was inserted percutaneously into each target cyst, and the contents were aspirated completely and submitted for culture. Some patients underwent aspiration of several infected cysts at the same time and the contents of each cyst were cultured. A drain was left in each cyst for one week after cyst fluid aspiration and daily lavage of the cyst cavity was performed with saline. We drained the cysts at various times after MEPM administration to investigate the relationship between the intracystic MEPM concentration and the time until drainage.

Identification of the isolates was performed using the MicroScan WalkAway 96 SI (Siemens Healthcare, Deerfield, IL, USA).

In all patients, a blood sample was collected just after completion of intravenous administration to measure the serum MEPM concentration. Most of the patients were on dialysis and had an arteriovenous fistula. Therefore, blood was collected from the wrist and antibiotics were administered into an antecubital vein of the same arm. The interval between MEPM administration and cyst puncture varied among the patients and the intracystic contents were sampled when a drain was placed into the infected cyst. Blood samples or cyst fluid samples were mixed with the same amount of 3-N-morpholino propane sulfonic acid buffer just after collection. The mixed samples were centrifuged for 10 min at 3000 rpm and then stored frozen at -80 °C. These samples were sent to the Department of Clinical Pharmaceutics, Faculty of Pharmaceutical Sciences, Doshisha Women’s College of Liberal Arts (Kyoto, Japan) in the frozen state, and all 300 μl of serum or cyst fluid was injected into an ultrafiltration device (Centrifree YM-30, Millipore) just after thawing. The MEPM concentration in plasma or cyst fluid was determined by injecting 30 μL of the filtrate obtained by centrifugation of the ultrafiltered sample at 3000 rpm for 5 min into a high-performance liquid chromatography (HPLC) system, which consisted of a liquid transport unit (LC-20AB, Shimadzu) and a spectrophotometer (SPD-20A, Shimadzu). The mobile phase was a mixture of PIC-A reagent/methanol (75:25), the flow rate was 1.0 mL/min, detection wavelength was 300 nm, and column was HYPERSIL ODS-5 (4.6 mm, L.D. × 250 mm; Chemco Scientific Co., Ltd.). For the assay using this system, the retention time of meropenem was 12.5 min, and lower limit of detection was 0.1 μg/mL. The intra-day and inter-day variation of MEPM measurement by this assay within 5% [8]. All measurements of MEPM were performed within 1 week after collection of samples from the patients. The residual rate of MEPM in plasma samples stored at -80 °C for 7 days after adding MOPS buffer was 99.5 ± 3.5% [8].

The MEPM concentration ratio between cyst fluid and serum was calculated as follows: cyst fluid MEPM concentration (μg/mL) / serum MEPM concentration (μg/mL) × 100 (%).

Results are expressed as the mean ± SD for data analyzed by parametric tests and as the median with interquartile range for data analyzed by non-parametric tests. A probability (P) value of less than 0.05 was defined as indicating significance. Univariate regression analysis was performed to analyze the relationship between the cyst fluid MEPM concentration and serum MEPM concentration (MEPM concentration ratio), as well as that between the cyst fluid MEPM concentration and the time until drainage after MEPM administration, and that between the MEPM concentration ratio and the time until drainage after MEPM administration.

All statistical analyses were performed with the JMP® 13.0 statistical software package (SAS Institute Inc., North Carolina, USA).