Application of microdialysis to cancellous bone tissue for measurement of gentamicin levels
JAC
Journal of Antimicrobial Chemotherapy (2004) 54, 263–265
DOI: 10.1093/jac/dkh291
Advance Access publication 9 June 2004
Application of microdialysis to cancellous bone tissue
for measurement of gentamicin levels
Lars B. Stolle1*, Magnus Arpi2, Peter Holmberg-Jørgensen3, Per Riegels-Nielsen4
and Johnny Keller3
1
Institute of Experimental Clinical Research and 2Department of Clinical Microbiology, Aarhus University
Hospital, Skejby Hospital, Brendstrupgaardvej, 8200 Aarhus; 3Department of Orthopaedic Surgery,
Aarhus University Hospital, Aarhus Hospitals, Nørrebrogade 44, 8000 Aarhus C; 4Department of
Orthopaedic Surgery, Esbjerg/Varde Hospital, Østergade 8, 6700 Esbjerg, Denmark
Received 2 January 2004; returned 8 March 2004; revised 26 March 2004; accepted 14 April 2004
Objectives: Knowledge concerning the distribution of antibiotics in bone tissue is valuable for pharmacokinetic and clinical use. Unfortunately, appropriate techniques are difficult to apply. We introduced
microdialysis catheters to cancellous bone tissue for the investigation of gentamicin levels and compared the pharmacokinetics measured with values obtained from bone samples.
Methods: After two microdialysis catheters had been inserted into cancellous bone, eight pigs received
an intravenous bolus of 240 mg of gentamicin. Microdialysates and bone samples were obtained over a
period of 6 h and drug concentrations were measured.
Results: The area under the curves of the two microdialysates and bone samples were 1569, 1721 and
1533 mg·min/L (ANOVA, P 5 0.81). Reproducibility of the measurements from the microdialysates was
defined as the mean ratio of AUC6/catheter no. 1/AUC6/catheter no. 2. This ratio was 1.02.
Conclusions: Microdialysis is a suitable, relatively non-invasive and reproducible technique for
dynamic and quantitative measurement of gentamicin levels in experimental research.
Keywords: experimental research, bioassays, bone samples, pharmacokinetics
Introduction
Most antibiotics exert their effect inside the interstitial space,
which is the site of surgical infections. It is therefore of great
clinical importance to obtain the pharmacokinetic profile at this
site, since effective treatment to inhibit bacterial growth demands concentrations that exceed the minimum inhibitory concentration.1
For decades, pharmacokinetics in bone tissue was investigated
through analysis of bone samples or exudates.2,3 Microdialysis,
which is minimally invasive, is a technique that allows dynamic
and continuous in vivo sampling. The principle is to introduce a
semi-permeable membrane into the tissue of choice. The membrane is perfused with a liquid that equilibrates with the fluid
outside the membrane by diffusion in both directions, thus
enabling dynamic measurements to be made.4 Recently, the distribution of gentamicin in cortical bone was investigated and no
differences were found between values obtained from bone
samples and microdialysates.5
The aim of this study was to introduce microdialysis to cancellous bone tissue for the measurement of gentamicin and compare the results to values obtained from bone samples.
Materials and methods
Animals and anaesthetic
Eight pigs [females, Danish Landrace Breed, 46.4 kg (range
42 – 48)] were included in the study. All animals underwent surgery
under general anaesthesia.5
Operative technique
Two holes with a diameter of 1.1 mm and depth of 15 mm were
drilled at an angle of 908 into cancellous bone in the right tibia, and
the microdialysis catheters were inserted into the channels. No postoperative exudation was observed after 1 h. In order to let the tissue
recover from insertion trauma, a period of 1 h was allowed before
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*Corresponding author. Tel: +45-89495511; Fax: +45-89496011; E-mail:
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JAC vol.54 no.1 q The British Society for Antimicrobial Chemotherapy 2004; all rights reserved.
L. B. Stolle et al.
starting the experiment. The positions of the catheters were controlled by autopsy.
Drugs
All animals received a bolus of 240 mg gentamicin (Garamycin;
Schering-Plough A/S) intravenously. Gentamicin was chosen because
of its low protein binding, and it has recently been investigated by
microdialysis.5 – 7
Microdialysis equipment
CMA 70 Microdialysis Brain Catheters (CMA/Microdialysis, Solna,
Sweden) and CMA 107 Microdialysis Infusion Pumps (CMA/Microdialysis) were used in this study. Flow rates of the pumps were
1 mL/min and isotonic saline with 1% albumin was chosen as
perfusate.
Figure 1. The standard curve for the investigation of gentamicin in cancellous bone. Data are presented as means ± S.E.M . of four parallel determinations (r = 0.98, P < 0.001).
Calibration of the probe
In vivo relative recovery of gentamicin was attained according to
retrodialysis.5 For this, two premanufactured concentrations of
gentamicin (4.4 and 8.7 mg/L) plus 1% albumin were added to
the perfusate. The in vivo relative recovery was calculated as follows: RR = 1 – (Cout/Cin) where Cout is the outlet concentration
(mg/L) and Cin is the inlet concentration (mg/L) of gentamicin.
The tissue concentration was defined as: Ctissue = 100 Cout
RR 1.
Dialysates were collected at 30 min and every hour until 6.5 h.
Since dialysates are time averaged over the collection interval, these
values were translated into concentrations at a single point by
assuming that the concentration obtained is the actual concentration
at the mid-point of the time interval.
Tissue and serum samples
Bone samples were taken from the left tibia with a Coombs Bone
Drill. The drill was placed perpendicular to the bone and standardized samples of 4 mm diameter and 5 mm height were obtained,
weighing 54.1 mg (3.1). Periosteum and cortical bone were removed
from all samples. Blood was collected from a sheath placed in the
external jugular vein. All samples were collected at 15 min and
every hour until 6 h. Samples were immediately frozen to 808C.
Assays of bone specimens
gentamicin. A P value below 0.05 was considered significant. The
pharmacokinetic measure used was the area under the curve from 0
to 6 h (AUC6) and was calculated by the trapezoid method. The tissue penetration was defin (...truncated)
