Why monitor serum levels of gentamicin?

An in vitro and ex vivo wound infection model to test topical and systemic treatment with antibiotics

AIMS

This study aimed to develop a wound infection model that could be used to test antibiotic-loaded electrospun matrices for the topical treatment of infected skin and compare the effectiveness of this treatment to systemically applied antibiotics.

METHODS AND RESULTS

3D-printed flow chambers were made in which Staphylococcus aureus biofilms were grown either on a polycarbonate membrane or explanted porcine skin. The biofilms were then treated either topically, by placing antibiotic-loaded electrospun matrices on top of the biofilms, or systemically by the addition of antibiotics in the growth medium that flowed underneath the membrane or skin. The medium that was used was either a rich medium or an artificial wound fluid. The results showed that microbial viability in the biofilms was reduced to a greater extent with the topical electrospun matrices when compared to systemic treatment.

CONCLUSIONS

An ex vivo infection model was developed that is flexible and can be used to test both topical and systemic treatment of wound infections. It represents a significant improvement over previous in vitro models that we have used to test electrospun membranes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The availability of a relatively simple wound infection model in which different delivery methods and dosage regimes can be tested is beneficial for the development of improved treatments for wound infections.

Real time monitoring of Staphylococcus aureus biofilm sensitivity towards antibiotics with isothermal microcalorimetry

Biofilm-associated infections with Staphylococcus aureus are difficult to treat even after administration of antibiotics that according to the standard susceptibility assays are effective. Currently, the assays used in the clinical laboratories to determine the sensitivity of S. aureus towards antibiotics are not representing the behaviour of biofilm-associated S. aureus, since these assays are performed on planktonic bacteria. In research settings, microcalorimetry has been used for antibiotic susceptibility studies. Therefore, in this study we investigated if we can use isothermal microcalorimetry to monitor the response of biofilm towards antibiotic treatment in real-time. We developed a reproducible method to generate biofilm in an isothermal microcalorimeter setup. Using this system, the sensitivity of 5 methicillin-sensitive S. aureus (MSSA) and 5 methicillin-resistant S. aureus (MRSA) strains from different genetic lineages were determined towards: flucloxacillin, cefuroxime, cefotaxime, gentamicin, rifampicin, vancomycin, levofloxacin, clindamycin, erythromycin, linezolid, fusidic acid, co-trimoxazole, and doxycycline. In contrast to conventional assays, our calorimetry-based biofilm susceptibility assay showed that S. aureus biofilms, regardless MSSA or MRSA, can survive the exposure to the maximum serum concentration of all tested antibiotics. The only treatment with a single antibiotic showing a significant reduction in biofilm survival was rifampicin, yet in 20% of the strains, emerging antibiotic resistance was observed. Furthermore, the combination of rifampicin with flucloxacillin, vancomycin or levofloxacin was able to prevent S. aureus biofilm from becoming resistant to rifampicin. Isothermal microcalorimetry allows real-time monitoring of the sensitivity of S. aureus biofilms towards antibiotics in a fast and reliable way.

Impact of High-Dose Anti-Infective Agents on the Osteogenic Response of Mesenchymal Stem Cells

Treatment of infected nonunions and severe bone infections is a huge challenge in modern orthopedics. Their treatment routinely includes the use of anti-infective agents. Although frequently used, little is known about their impact on the osteogenesis of mesenchymal stem cells. In a high- and low-dose set-up, this study evaluates the effects of the antibiotics Gentamicin and Vancomycin as well as the antifungal agent Voriconazole on the ability of mesenchymal stem cells to differentiate into osteoblast-like cells and synthesize hydroxyapatite in a monolayer cell culture. The osteogenic activity was assessed by measuring calcium and phosphate concentrations as well as alkaline phosphatase activity and osteocalcin concentration in the cell culture medium supernatant. The amount of hydroxyapatite was measured directly by radioactive ^99mTechnetium-HDP labeling. Regarding the osteogenic markers, it could be concluded that the osteogenesis was successful within the groups treated with osteogenic cell culture media. The results revealed that all anti-infective agents have a cytotoxic effect on mesenchymal stem cells, especially in higher concentrations, whereas the measured absolute amount of hydroxyapatite was independent of the anti-infective agent used. Normed to the number of cells it can therefore be concluded that the above-mentioned anti-infective agents actually have a positive effect on osteogenesis while high-dose Gentamycin, in particular, is apparently capable of boosting the deposition of minerals.

Vestibular Toxicity Due to Gentamicin in Peritoneal Dialysis Patients

Gentamicin is well known to be a cause of vestibular toxicity. Despite this, gentamicin is often used to treat peritonitis and exit site infections in peritoneal dialysis patients because of the ease of intraperitoneal administration and the broad coverage of aerobic Gram-negative bacilli, including Pseudomonas aeruginosa. We report 4 cases of severe vestibular toxicity occurring in peritoneal dialysis patients treated with gentamicin. They were all treated as outpatients for peritonitis or an exit-site infection while on continuous ambulatory peritoneal dialysis (CAPD) or continuous cyclic peritoneal dialysis (CCPD). The drug was administered to 3 patients in each peritoneal exchange (5 mglL) after a loading dose. A fourth patient was given 1 mglkg of intraperitoneal gentamicin every other day. The mean length of treatment was 21 days. Levels were not used to adjust the doses. All developed severe vertigo from which there was incomplete or no recovery. We suggest that gentamicin and the other aminoglycosides should be used in peritoneal dialysis patients only when there is no suitable alternative antibiotic. When gentamicin is administered, levels should be carefully followed. Studies should be performed in peritoneal dialysis patients on the feasibility of dosing gentamicin intermittently, which may be less toxic than continuous intraperitoneal administration.

Extended-interval gentamicin dosing in achieving therapeutic concentrations in malaysian neonates

OBJECTIVE

To evaluate the usefulness of extended-interval gentamicin dosing practiced in neonatal intensive care unit (NICU) and special care nursery (SCN) of a Malaysian hospital.

METHODS

Cross-sectional observational study with pharmacokinetic analysis of all patients aged ≤28 days who received gentamicin treatment in NICU/SCN. Subjects received dosing according to a regimen modified from an Australian-based pediatric guideline. During a study period of 3 months, subjects were evaluated for gestational age, body weight, serum creatinine concentration, gentamicin dose/interval, serum peak and trough concentrations, and pharmacokinetic parameters. Descriptive percentages were used to determine the overall dosing accuracy, while analysis of variance (ANOVA) was conducted to compare the accuracy rates among different gestational ages. Pharmacokinetic profile among different gestational age and body weight groups were compared by using ANOVA.

RESULTS

Of the 113 subjects included, 82.3% (n = 93) achieved therapeutic concentrations at the first drug-monitoring assessment. There was no significant difference found between the percentage of term neonates who achieved therapeutic concentrations and the premature group (87.1% vs. 74.4%), p = 0.085. A total of 112 subjects (99.1%) achieved desired therapeutic trough concentration of <2 mg/L. Mean gentamicin peak concentration was 8.52 mg/L (95% confidence interval [Cl], 8.13-8.90 mg/L) and trough concentration was 0.54 mg/L (95% CI, 0.48-0.60 mg/L). Mean volume of distribution, half-life, and elimination rate were 0.65 L/kg (95% CI, 0.62-0.68 L/kg), 6.96 hours (95% CI, 6.52-7.40 hours), and 0.11 hour(-1) (95% CI, 0.10-0.11 hour(-1)), respectively.

CONCLUSION

The larger percentage of subjects attaining therapeutic range with extended-interval gentamicin dosing suggests that this regimen is appropriate and can be safely used among Malaysian neonates.

The Pharmacology of Aminoglycosides—I. Considered as a Group

This review of aminoglycoside pharmacology will appear in two parts. The first segment summarizes general information applicable to all agents, such as aspects of absorption, distribution, and clearance. The subsequent article will focus on specific agents currently in use in clinical practice: gentamicin, tobramycin, netilmicin, amikacin, streptomycin, and kanamycin, highlighting toxicities and pharmacokinetic-based dosing strategies.

Embedded in the history of antimicrobial agents with the discovery of streptomycin in 1944, the aminoglycosides remain a mainstay of contemporary antibiotic therapy. Noteworthy features include rapid bactericidal activity against aerobic gram-negative organisms as well as additive or synergistic activity when coadministered with beta-lactam agents. These positive attributes are offset by limited penetration into various body fluids and tissues, and dose (concentration) related renal and ototoxicity. Despite the proliferation of safer beta-lactam compounds with expanded antimicrobial spectrums, the aminoglycosides are still initial drugs of choice for most life-threatening, aerobic, gram-negative infections. Used in combination with anti-pseudomonal penicillins, the aminoglycosides are the agents of choice for empiric therapy of fever in the neutropenic host or documented tissue infection with Pseudomonas aeruginosa.

Aminoglycoside-induced nephrotoxicity--a focus on monitoring: a review of literature

The use of aminoglycoside (AG) antibiotics has declined over the past 15 years primarily due to comparable potency of other antimicrobials and the nephrotoxicity potential of AG drugs. However, resurgence in the use of AG antimicrobials is occurring due to multidrug-resistant gram-negative nosocomial infections. Multidrug-resistant Pseudomonas and Acinetobacter isolates as well as extended-spectrum beta-lactamase-producing Enterobacteriaceae continue to force clinicians to consider AG therapy for nosocomial infections in hospitalized patients and enterococcal endocarditis. Additionally, AGs are still indicated in the treatment of pulmonary exacerbations of cystic fibrosis. Along with the use of AG antibiotics is the associated renal insufficiency complication. This review discusses the mechanism for AG-induced nephrotoxicity. Patient- and drug-related risk factors are discussed to help identify patients at increased risk. The issue of serum-level monitoring is discussed relative to the development of nephrotoxicity.

Amikacin population pharmacokinetics among paediatric burn patients

INTRODUCTION

The objectives of this study were to (1) determine the pharmacokinetics of amikacin among children with severe burn and (2) identify influential covariates.

METHODS

Population-based pharmacokinetic modelling was performed in NONMEM 7.2 for hospitalized children who received amikacin at 10-20mg/kg divided two, three, or four times per day as part of early empiric treatment of presumed burn-related sepsis.

RESULTS

The analysis included data from 70 patients (6 months to 17 years) with 282 amikacin serum concentrations. Amikacin's mean Cmax was 33.2±9.4μg/mL and the mean Cmin was 3.8±4.6μg/mL. The final covariate model estimated clearance as 5.98L/h/70kg (4.97-6.99, 95% CI), the volume of distribution in the central compartment as 16.7L/70kg (14.0-19.4, 95% CI), the volume of distribution in the peripheral compartment as 40.1L/70kg (15.0-80.4, 95% CI), and the inter-compartmental clearance as 3.38L/h/70kg (2.44-4.32, 95% CI). In multivariate analyses, current weight (P<0.001) was a significant covariate, while age, sex, height, serum creatinine, C-reactive protein, platelet count, the extent and type of burn, and concomitant vancomycin administration did not influence amikacin pharmacokinetics.

DISCUSSION

Children with burn featured elevated amikacin clearance when compared to healthy adult volunteers. However, peak amikacin concentrations are comparable to those attained in other critically-ill children, suggesting that elevated amikacin clearance may not result in sub-therapeutic antibacterial effects. In this study, we found that amikacin displays two-compartment pharmacokinetics, with weight exerting a strong effect upon amikacin clearance. Further pharmacodynamic studies are needed to establish the optimal dosing regimen for amikacin in paediatric burn patients.

Acute renal failure after topical fortified gentamicin and vancomycin eyedrops

PURPOSE

To report a case of acute renal failure after topical fortified gentamicin and vancomycin eyedrops in the treatment of endophthalmitis.

METHODS

A 67-year-old lady with diabetes mellitus was treated for bleb-related endophthalmitis. After intravitreal antibiotics, she was given oral ciprofloxacin, fortified gentamicin, and vancomycin eyedrops. She developed acute renal failure a few days after therapy. Blood tests and ultrasound of the urinary system were performed to investigate for the cause of the renal failure.

RESULTS

No apparent cause of renal failure could be identified in our patient. Autoimmune markers and ultrasound of the urinary system were unremarkable. Fortified gentamicin and vancomycin eyedrops were stopped on day 9 and 13, respectively. The renal function recovered dramatically. The gentamicin level was checked 2 days after it had been stopped, and the serum level was 0.34 mg/L. Renal function improved on supportive management without dialysis. Serum creatinine level completely normalized 2 months later.

CONCLUSIONS

This is the first article that demonstrated a detectable level of serum gentamicin level after usage of topical eyedrops. This is also the first article demonstrating that nephrotoxicity of topical fortified gentamicin and vancomycin eyedrops was found. The acute renal failure in our patient recovered completely after cessation of the eyedrops.

A bioactive sol-gel glass implant for in vivo gentamicin release. Experimental model in Rabbit

Biomaterial pieces with osteogenic properties, suitable for use in the treatment of bone defects, were synthesized. The materials, which avoid bone infections, are exclusively composed of gentamicin sulfate and bioactive SiO2-CaO-P2O5 sol-gel glass (synthesized previously), and were manufactured by means of uniaxial and isostatic pressure of the mixed components. After implanting the pieces into rabbit femur, we studied (1) antibiotic release, determining the concentration in proximal and distal bone, liver, kidney, and lung as a function of time, and (2) bone growth as a consequence of the glass reactivity in the biological environment. The results demonstrated that the implants are good carriers for local gentamicin release into the local osseous tissue, where they show excellent biocompatibility and bone integration. Moreover, these implants are able to promote bone growth during the resorption process.

Uptake of gentamicin by bullfrog saccular hair cells in vitro

Vertebrate sensory hair cells in the inner ear are pharmacologically sensitive to aminoglycoside antibiotics. Although the ototoxicity of aminoglycosides is well known, the route of drug uptake by hair cells and mechanisms of cytotoxicity remain poorly understood. Previously published studies have documented the intracellular distribution of gentamicin using immunocytochemical, electron microscopic, and autoradiographic methods. In this article, we compare the subcellular distribution of fluorescently conjugated gentamicin (gentamicin-Texas Red, GTTR) with immunolabeled gentamicin using confocal or electron microscopy. Gentamicin (detected by postfixation immunocytochemistry) and GTTR were rapidly taken up by hair cells throughout the bullfrog saccular explant in vitro and preferentially in peripheral hair cells. Immunolabeled gentamicin and GTTR were observed at the apical membranes of hair cells, particularly in their hair bundles. GTTR was also identified within a variety of subcellular compartments within hair cells, including lysosomes, mitochondria, Golgi bodies, endoplasmic reticulum, and nuclei, and in similar structures by immunoelectron microscopy. The distributions of GTTR and immunolabeled gentamicin are largely identical and corroborate a variety of published immunocytochemical and autoradiography studies. Thus, GTTR is a valid fluorescent probe with which to investigate the pharmacokinetics and mechanisms of gentamicin accumulation.

Biocompatibility and in vivo gentamicin release from bioactive sol-gel glass implants

Biomaterial pieces, with suitable osteogenic properties for use in the treatment of bone defects and the capability to avoid bone infections, have been synthesized. These materials are composed exclusively of gentamicin sulfate and bioactive SiO(2)-CaO-P(2)O(5) sol-gel glass (previously synthesized). Implant processing was achieved by uniaxial and isostatic pressure of the components mixture. After implanting the pieces into rabbit femur, we studied (i) the antibiotic release, determining the concentration in proximal and distal bone, liver, kidney, and lung as a function of time; and (ii) the bone growth resulting from the glass reactivity in the biologic environment. The results indicate that the implants are good carriers for local gentamicin release in the osseous tissue, exhibiting excellent biocompatibility and bone integration. Moreover, these implants are able to promote bone growth during their resorption process.

Pharmacological issues in the treatment of tuberculosis

A thorough review of the clinical trial data combined with new in vitro experimental information may make the optimization of dosages of TB drugs possible. Several factors can affect the selection and dosage of TB drugs including hepatic and renal impairment, pregnancy, duration of disease before treatment, and extent of debilitation. Drug interactions and pharmacodynamics must be considered, and their roles are discussed.

Pharmacokinetic analysis of amikacin twice and single daily dosage in immunocompromised pediatric patients

Ten children received amikacin twice daily and 13 were treated using the single daily protocol. All had fever and neutropenia on admission, and received a total daily dose of 20 mg/kg when included in the study. Individual pharmacokinetic parameters were calculated using a one-compartment model for two blood amikacin samples. The mean (+/- SD) of elimination half-life (h), amikacin clearance (l/h/kg), volume of distribution (l/kg), peak concentration (microgram/ml) and trough concentration (microgram/ml) were: 2.51 (0.74) and 2.85 (0.32) h; 0.26 (0.16) and 0.115 (0.02) l/h/kg; 0.74 (0.44) and 0.47 (0.11) l/kg; 19.1 (12.3) and 42.6 (12.6) micrograms/ml; 0.85 (0.74) and 0.18 (0.24) microgram/ml with twice and single daily dosage schedules, respectively. A single daily dose of amikacin had a significantly longer elimination half-life, lower clearance, higher peak concentration and lower trough concentration in comparison to the twice-daily schedule. The use of amikacin 20 mg/kg daily delivered in a single daily dose is recommended for immunocompromised pediatric patients with fever and neutropenia, in spite of the measured pharmacokinetic differences.

Pharmacokinetic analysis of gentamicin thrice and single daily dosage in pediatric cancer patients

Fifty-two children suffering from different types of malignancies were included and evaluated for the pharmacokinetics of gentamicin thrice or single daily dosage protocols. All the study population received a total dose of 5 mg/kg daily. Thirty children received gentamicin thrice daily, and 22 were treated using the single daily protocol; all had fever and neutropenia when included. The individual pharmacokinetic parameters were calculated using a one-compartment model for two blood gentamicin samples. The mean (SD) t 1/2 (h), clearance (mL/min/BSA), Vss (L/kg), Cmax (micrograms/mL), and Cmin (micrograms/mL) were 3.05 (1.0) and 3.9 (0.6) h, 136 (61.3) and 99.9 (65.3) mL/min/BSA, 0.4035 (0.167) and 0.457 (0.17) L/kg, 5.2 (2.0) and 11.5 (4.2) micrograms/mL, 0.8 (0.6) and 0.18 (0.1) microgram/mL for thrice and single daily dosage schedules, respectively. The single gentamicin daily dose protocol had a significantly longer t 1/2, shorter clearance normalized to BSA, higher Cmax, and lower Cmin in comparison with the thrice daily schedule. We recommend the use of gentamicin at 5 mg/kg daily delivered as a single daily dose for pediatric cancer patients with fever and neutropenia, in spite of the measured pharmacokinetic differences, which in our opinion have no clinical significance.

Correlation between nephrotoxicity and pharmacokinetic parameters of gentamicin

Gentamicin pharmacokinetics were determined in 26 critically ill adult patients. All had normal or only moderately reduced renal function based on serum creatinine concentration and clearance. The average half-life of elimination was 4.68 h, creatinine clearance was 3.9 l/h, and gentamicin clearance was 2.86 l/h. There was a highly significant correlation between the area under the serum concentration-time curves (AUC) and the peak and trough concentrations (r = 0.908, 0.980, P < 0.05, respectively). Serum gentamicin concentrations rose rapidly in 10 patients who showed deterioration of kidney function after 5 days of therapy. Gentamicin peak concentrations increased by 31%, while trough concentration increased by 121%. The mean percentage change in half-life was 68.49%, while the mean percentage change in renal function was 44.38%. Linear regression analysis of AUC versus the percentage change in kidney function revealed a significant increase in AUC with decrease in kidney function (r = 0.909, P < 0.05). There was a significant increase in half-life with decrease in kidney function (r = 0.948, P < 0.05).

Variation in the pharmacokinetics of gentamicin and tobramycin in patients with pleural effusions and hypoalbuminemia

The pharmacokinetic parameters of gentamicin and tobramycin were evaluated and compared for 260 patients with pleural effusions and 1,049 patients without pleural effusions by chest radiograph. Pharmacokinetic data were collected prospectively and analyzed by using our aminoglycoside data base. Univariate analysis revealed that the patients with pleural effusions demonstrated significantly lower serum albumin concentrations, greater aminoglycoside volumes of distribution, longer elimination half-lives, and lower peak and higher trough concentrations in serum than the patients without pleural effusions. Patients with pleural effusions were significantly older and had lower total body weight. Stepwise multiple linear regression analysis revealed that lower total body weight and serum albumin concentration, presence of pleural effusion, and greater age were associated with significantly greater volumes of distribution. Calculated creatinine clearance, age, total body weight, and shock were associated with reduced aminoglycoside clearance in these patients.

Prediction of netilmicin disposition in neonates

Multiple regression analyses of data from 33 neonates who received netilmicin therapy showed that concurrent treatment with other drugs (Drg), creatinine clearance (CLcr), gestational age (GA), and an apgar score of less than 6 at 1 min (Agl') were significant determinants of netilmicin clearance. Apparent volume of distribution was significantly affected by postnatal age (PNA), gender, the presence of ascites and/or oedema (A/O), and whether or not the neonate was small for gestational age (SGA). The following formulae were obtained: [formula: see text] The regression formulae were shown to predict netilmicin plasma concentrations with good precision and a non-significant bias in a further 15 neonates studied prospectively.

Screening for aminoglycoside auditory toxicity in the old

1. We have investigated 22 patients receiving gentamicin, mean (s.d.) age 78 (6) years for auditory toxicity, using a standard audiometric technique in a sound-treated room (Study 1). 2. Use of a portable audiometer might allow a larger and more representative proportion of patients treated with aminoglycosides to be screened for ototoxicity. A method for detecting high frequency loss suitable for use in the ward was evaluated in 12 volunteers aged 27 (4) years (Study 2). 3. The error inherent in taking hearing at the start of treatment as a reference point was measured in 16 patients, aged 81 (8) years, prescribed non-ototoxic antibacterials (Study 3). 4. A significant (P = 0.05) reduction in hearing threshold was detected in Study 1, although psychometric tests revealed unchanged or improved ability to co-operate. This occurred only at 4000 Hz, the highest frequency used. The magnitude of this loss, mean 2.5 dB, was similar to that of the improvement in threshold detected (P = 0.0004) early in the course of treatment in Study 3. Thus, underestimation of ototoxicity is likely. 5. If a change of threshold of 10 dB or more is taken arbitrarily to represent a real change in hearing, then there was a significant excess of patients in Study 1 with losses at 4000 Hz only (P = 0.032). The six with such losses at this frequency were older than the rest. However, there was a significant (P less than 0.02) positive correlation between log mean predose serum gentamicin concentration and age. Thus, it remains to be determined whether presbyacusis sensitizes those hair cells which it does not destroy to toxic damage. 6. The cumulative dose of gentamicin (for a course of the duration given) was calculated according to published prescribing aids. There was no systematic reduction in the ratio of the dose recommended by a given aid to the dose prescribed in the six with hearing losses as defined above. 7. In Study 2, thresholds obtained at 6000 Hz in the open ward were, on average, 0.9 dB higher than in the sound treated room, but the effect of venue did not reach statistical significance. In the morning thresholds were marginally, but significantly (P = 0.04), lower than in the afternoon. Precision, as measured by the standard deviation of replicate determination, was independent of test conditions. Using multiple (ten) threshold determinations appeared to improve resolution.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased aminoglycoside dosage requirements in hematologic malignancy

Aminoglycoside pharmacokinetic parameters were studied prospectively in 27 patients with an underlying hematologic malignancy and fever associated with neutropenia and in 18 control patients. Pharmacokinetic parameters and dosages were determined by linear regression analysis of a one-compartment model by the method of Sawchuk et al. (R. J. Sawchuk, D. E. Zaske, R. J. Cippolle, W. A. Wargin, and R. G. Strate, Clin. Pharmacol. Ther. 21:362-369, 1976). Significant differences between the study and control groups were found for aminoglycoside volume of distribution (0.40 +/- 0.1 versus 0.27 +/- 0.05 liter/kg [mean +/- standard deviation], respectively; P less than 0.0001), clearance (116.6 +/- 48.9 versus 68.6 +/- 26.7 ml/min, respectively; P less than 0.0001), half-life (2.27 +/- 0.66 versus 3.5 +/- 1.8 h, respectively; P less than 0.0001), and elimination rate constant (0.33 +/- 0.11 versus 0.24 +/- 0.09 h-1, respectively; P less than 0.001). The percentage of bone marrow blast cells (at the time of diagnosis) in patients with acute leukemia significantly correlated with increased aminoglycoside clearance (R2 = 36.98%; P = 0.0001). Patients with stage IV lymphomas (Hodgkins disease and non-Hodgkins lymphoma) had a significantly increased clearance compared with patients with lower stages of lymphomas (105.1 +/- 18.5 versus 84.1 +/- 14.9 ml/min; P = 0.014). Fever, leukocyte count, or chemotherapy, among other clinical and laboratory parameters that were studied, had no significant correlation or effect on aminoglycoside disposition. The average dose of amikacin required to maintain peak concentrations in serum above 20 micrograms/ml in patients with a hematologic malignancy was 27.5 +/- 8.43 mg/kg per day. Pharmacokinetic parameters and dosages for the control patients were comparable to general literature standards. we conclude that the dosages recommended by the manufacturers or those derived from nomograms underestimate the aminoglycoside volume of distribution and clearance in patients with a hematologic malignancy and result in suboptimal peak aminoglycoside concentrations in serum. We recommend that in febrile neutropenic patients with an underlying hematologic malignancy, amikacin be initiated at 7.5 to 10 mg/kg per dose every 8 h (2 to 2.5 mg/kg per dose every 8 h for gentamicin) and adjusted within 24 h based on individual pharmacokinetic analysis.

Amikacin once daily: a new dosing regimen based on drug pharmacokinetics

Once-daily dosing of amikacin is a novel therapy regimen which seems pharmacokinetically appropriate for the primary group of patients considered for aminoglycoside therapy. In this study of 29 elderly patients with serious infections, amikacin 11 mg/kg or 15 mg/kg bw was administered as a short-term (30 min) intravenous infusion. The amikacin serum concentration-time profile was best described by a bi-exponential equation with a half-life of about 4.8 h. A triexponential equation was not applicable because the slow terminal elimination phase was not detected during the 24 h dosing interval. In practice, a uni-exponential equation is often used, and this may lead to incorrect conclusions about the elimination rate of amikacin. Amikacin clearance provides more direct information about elimination of amikacin than does serum half-life. Thus, there was a better correlation between the individual amikacin clearances and creatinine clearances (r = 0.89), than between the serum half-lives of amikacin and the creatinine clearances (r = 0.71). For elderly patients a smaller dose of amikacin than the regular daily dose of 15 mg/kg bw, i.e. about 11 mg/kg bw, seems recommendable, when it is given once daily. From the data obtained it is also obvious that once-daily dosing of amikacin does not eliminate the need for checking serum concentrations of the drug.

Antibiotic therapy for Pseudomonas aeruginosa bacteremia: outcome correlations in a prospective study of 200 patients

PURPOSE AND PATIENTS AND METHODS

We performed a prospective clinical study of 200 consecutive patients with Pseudomonas aeruginosa bacteremias to analyze in vitro susceptibility and synergistic testing of antibiotics the patients received and clinical parameters to assess their relationship to survival.

RESULTS

No significant correlation between in vitro susceptibility testing (minimal inhibitory concentrations/minimal bactericidal concentrations) and outcome could be demonstrated. Similarly, improved outcome could not be demonstrated for patients receiving antibiotic combinations that were synergistic in vitro (either time-kill or checker-board) versus those combinations that were not. There was also no correlation between results obtained by time-kill curve and checkerboard synergistic testing, i.e., combinations found to be synergistic by one method were not necessarily synergistic by the other method. Clinical parameters associated with improved survival were a urinary portal of entry and absence of neutropenia. Conversely, survival was significantly decreased when the portal was the respiratory tract. The mortality rate between patients receiving combination therapy (27%) and monotherapy (47%) was significant (p less than 0.02); this significant relationship held true for most subgroups including malignancy, nosocomial infection, and infection site.

CONCLUSION

Increasing effort should be placed on ensuring timely administration of combination therapy to patients with P. aeruginosa bacteremia since the use of combination therapy was even more important in determining outcome than was underlying disease.

Antimicrobial therapy for pediatric patients

New antimicrobial agents are being introduced for clinical use at an increasingly rapid rate. This has required physicians continually to review relevant data and determine unique properties that might guide selection among any new antibiotics as well as older ones. Efficacy, potential toxicity, and comparative cost (in that order) generally guide selection. The present comprehensive review examines currently available antibiotics along with some under investigation, emphasizing these three basic areas of consideration.

Population pharmacokinetics of tobramycin

1. Population pharmacokinetic parameters of tobramycin were determined in a heterogenous group of 97 patients using serum samples drawn for the routine monitoring of tobramycin concentrations, following multiple dosing regimens. 2. To describe the accumulation kinetics of tobramycin a two-compartment pharmacokinetic model was required. The best fit to the data was obtained when drug clearance (1 h-1) was related linearly to creatinine clearance (proportionality constant: 0.059 +/- 0.002 x CLcr (ml min-1)) and initial volume of distribution (1) was related linearly to body weight (proportionality constant: 0.327 +/- 0.014 x body weight (kg)). The intersubject variability in these two parameters was 32% and 3%, respectively, whilst the residual or intrasubject variability amounted to 21% of the tobramycin concentration. The terminal half-life of tobramycin, 26.6 +/- 9.4 h, was appreciably shorter than previously reported. 3. The population pharmacokinetic model was validated against data obtained from 34 independent patients and the predicted and observed concentrations were found to be in good agreement. The population pharmacokinetic model was used to design a priori dosing recommendations for tobramycin.

Optimization of blood sampling time after intravenous bolus doses of gentamicin

Comparisons were made, based on a one-compartment model, between predicted serum concentrations obtained at various sampling times after i.v. bolus and i.m. injections of gentamicin. Post-dose concentrations 1 h after i.m. injection were within 3% of the maximum concentration at steady-state, indicating that this was the optimal sampling time. Serum concentrations 1 h post-i.v. bolus were less than 7% different from those 1 h post-i.m. injection. In a clinical trial, blood samples taken earlier during the distribution phase of the drug, after an i.v. bolus, resulted in serum concentrations which were up to 74% higher than concentrations at 1 h. A survey of a sample of U.K. hospitals showed that only 41% were taking samples at 1 h post i.v. bolus of gentamicin. The majority of hospitals recommended a range of post-dose serum concentrations between 4 and 12 mg/l for patients with septicaemia, but when adjusted for errors related to sampling time, 36% of hospitals recommended a minimum which was equivalent to less than 4 mg/l at 1 h post dose. Post-dose concentrations of gentamicin should be measured in samples taken 1 h after either i.v. bolus and i.m. injections.

Pharmacokinetic estimation for therapeutic dosage regimens (PETDR)--a software program designed to determine intravenous drug dosage regimens for veterinary applications

Pharmacokinetic estimation for therapeutic dosage regimens (PETDR) is a soft-ware program used to design individualized intravenous dosage regimens, determine concentration-time profiles, predict serum concentrations at a specific time after intravenous dosing and predict the time after the last dose to achieve a specified concentration of drug. The reference pharmacokinetic parameters may be based on an individual animal's pharmacokinetic disposition of drug or on FARAD (Food Animal Residue Avoidance Databank) mean population kinetic parameters. An individual animal's kinetic parameters may be input for predetermined analysis or the program can calculate these values by input of raw serum concentration-time data. The program allows the user to specify certain parameters of the dosage regimen, then calculates the other parameters (given desired maximum and minimum serum concentrations, dose and interval are calculated; given desired maximum serum concentration and interval, dose is calculated, etc.). Given the kinetic parameters, the dose and dosing interval, the program calculates and plots the serum concentration-time profile of the drug for that animal. The time and the number of doses to reach steady state can be calculated as well as the determination of loading dose. The percentage of the time of a dosing interval at steady state that the serum concentration is above a specific minimum inhibitory concentration (MIC) allows evaluation of efficacy of an antimicrobial regimen. Similarly, the time to reach a specific concentration (e.g. residue tolerance) or the MIC of a drug can be calculated. Legal tissue tolerances can be accessed from FARAD to aid in predicting for what period of time illegal residues will remain in the animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoglycoside antibiotics in clinical use

Aminoglycosides are among the most used antibiotics despite competitive pressure from newer beta-lactam agents. The activity profile, pharmacology, toxicity potential, and methods of toxicity prevention of aminoglycosides are well appreciated after three decades. Nephrotoxicity, ototoxicity, and the added costs of drug level monitoring limit wider usage, but great activity against highly antibiotic resistant gram negative bacteria often outweigh these disadvantages and will likely keep aminoglycosides available for the foreseeable future.

Relationship of serum antibiotic concentrations to nephrotoxicity in cancer patients receiving concurrent aminoglycoside and vancomycin therapy

Methicillin-resistant coagulase-negative staphylococci have become increasingly responsible for febrile episodes in cancer patients, often necessitating the addition of vancomycin to an aminoglycoside-containing broad-spectrum antibiotic regimen. A total of 229 courses of antibiotic therapy in 229 patients were evaluated for nephrotoxicity associated with the administration of an aminoglycoside and/or vancomycin. The incidence of nephrotoxicity observed in patients administered an aminoglycoside (Group A) was 18 percent; vancomycin (Group B) 15 percent; and an aminoglycoside concurrently with vancomycin (Group C) 15 percent. The following pharmacokinetic/dosing factors were significantly associated with increased nephrotoxicity in the groups: baseline serum creatinine level, mean daily dose during the first three days of therapy (Group B), and elevated serum trough aminoglycoside or vancomycin concentrations (2 micrograms/ml or more or 10 micrograms/ml or more, respectively). No cumulative nephrotoxicity was demonstrated with the concurrent administration of vancomycin and an aminoglycoside. A higher incidence of nephrotoxicity was seen in Group C (42 percent) and Group B (27 percent) patients, in whom trough serum vancomycin concentrations were 10 micrograms/ml or more.

Clinical pharmacokinetics, toxicity and cost effectiveness analysis of aminoglycosides and aminoglycoside dosing services

This article reviews the clinical pharmacokinetics, clinical toxicity and cost-effectiveness analysis of aminoglycosides and of dosing services for aminoglycosides. The reader is referred elsewhere for a review of the pharmacology, antimicrobial spectrum of activity and clinical use of these drugs. A critique of the more commonly used methods of aminoglycoside dosage determinations is included, based on the inter-individual variation in aminoglycoside disposition parameters. The advantages and disadvantages of arbitrary, predictive, and pharmacokinetic methods of dosing determination are summarized. Justification for the routine determination of serum aminoglycoside concentrations is reviewed. We review the lack of standardization of definitions for aminoglycoside-associated nephrotoxicity in published studies, and studies which illustrate these differences are highlighted. Evidence for the association between serum aminoglycoside concentrations and nephrotoxicity is examined. Ototoxicity is similarly reviewed. The concept of cost-effectiveness analysis is examined extensively in this review. We discuss the literature concerning the cost benefit analysis of drug dosing services.

Drug concentrations. A guide to their usefulness in clinical practice

When used properly, measurements of plasma drug levels in the clinical setting may provide valuable information. Optimally the drug level will permit the clinician to devise a therapeutic regimen on the basis of an individual patient's handling of the drug and thus obtain maximal drug efficacy while minimizing the risk of drug toxicity. However, the technology that permits the measurement of drug levels has often outpaced the clinical data base that allows proper interpretation of the level. Thus, the physician should be aware of both the potential and the limitations of therapeutic drug monitoring and apply the technique critically with respect to individual drugs in individual patients.

Auditory brainstem response in young burn-wound patients treated with ototoxic drugs

Burn-wound patients often require potentially ototoxic doses of aminoglycoside drugs in the treatment of gram-negative sepsis. Cochlear hearing impairment may be an unfortunate consequence of this medical therapy. We evaluated auditory sensitivity with the auditory brainstem response (ABR) in a group of 32 children with acute, severe thermal burns ranging in age from 18 months to 17 years. The mean percent of total body surface area burns was 64%. None of the subjects had a known history of hearing deficits or aminoglycoside therapy, and all yielded a normal baseline ABR upon hospital admission. Eight of the subjects (22%) showed either an abnormal ABR, or no response, at 40 dB prior to hospital discharge. The medical treatment for this group of subjects (gentamicin, amikacin, vancomycin, amphotericin B) was compared to that of a second subgroup of 7 subjects without auditory deficit but with a statistically comparable percentage of burns. The mean dosage of vancomycin was higher for the auditory impairment group than for the unimpaired group. Prediction of ototoxicity in the acute burned patient is extremely difficult as there are numerous factors that may influence the risk of cochlear damage. We conclude, however, that the ABR can be applied in early detection of auditory deficit. Follow-up audiometric assessment is advisable since auditory deficits in this population may be delayed or progressive after discontinuance of drug therapy.

A simplified model for adjustment of gentamicin dosage in newborn infants

In a retrospective study of 72 neonates during treatment with gentamicin, poor correlation was found between dosage based on body weight and gentamicin serum concentrations. Calculation of adequate gentamicin dosage regimen during steady-state based on individual pharmacokinetic parameters according to Gibaldi & Perrier was then studied in 35 newborn infants during therapy. Predictions were based on gentamicin serum concentrations taken prior to and 1, 3, and 5 hours after the first (n = 8) or second (n = 12) dose (group A), or only prior to and one hour after dose (group B, n = 15). Half-life (t1/2), apparent volume of distribution (Vd), body clearance (Clbody) and elimination rate constant (beta) were not significantly different when calculated after the first or second dose or during steady-state. The correlation between predicted and observed gentamicin concentration was high in both groups (p less than 0.005) and the slopes congruent with unity. After dose or interval correction, 73% of the observed predose concentrations (mean 2.0 micrograms/ml) were within 1 microgram/ml of predicted values. One hour after dose the predicted (mean 5.7 micrograms/ml) and observed (mean 6.2 micrograms/ml) values were not significantly different. Higher precision was noted when the predictions were based on 4 samples (group A) compared to 2 (group B). Since the calculations may be performed by a simple desk calculator rapid advice may be given to the clinical staff on adequate gentamicin dosage even in small severely ill preterm infants.

Dibekacin assay in serum by automated fluorescence polarization immunoassay (Abbott Tdx): Comparison with high-performance liquid chromatography, substrate-labelled fluorescent immunoassay and radioimmunoassay

An immunoassay based on fluorescence polarization detection (FPIA) has been recently adapted for dibekacin. This has been compared with a reference method (high-performance liquid chromatography), and two other methods used in clinical laboratories for monitoring this aminoglycoside, namely substrate-labelled fluorescent immunoassay (SLFIA) and radioimmunoassay (RIA). FPIA was fast and more reliable than SLFIA or RIA, and offered therefore superior performance. However, its nominal cost per assay is high.

Randomized trial of imipenem/cilastatin versus gentamicin and clindamycin in mixed flora infections

Results of a randomized trial comparing imipenem/cilastatin versus the combination of gentamicin plus clindamycin for mixed flora surgical sepsis are reported herein. Seventy-four patients were evaluable, 50 of whom had intra-abdominal sepsis. No imipenem-resistant initially infecting isolates were encountered. When outcome was evaluated on the basis of severity scoring (APACHE II), no difference in mortality was noted. However, therapy in two patients with Pseudomonas emerging from a polymicrobial flora failed with gentamicin, whereas no Pseudomonas failures were noted with imipenem/cilastatin. The major difference noted was in toxicity. There was a 20 percent incidence of nephrotoxicity in gentamicin-treated patients despite serum level monitoring and multiple dose adjustments. The degree of efficacy and the relative tolerability of imipenem/cilastatin in seriously ill surgical patients is demonstrated.

Measurement of tobramycin concentrations in saliva

Paired serum and saliva specimens were obtained from 16 patients and three volunteers who had received tobramycin. In addition, saliva was collected from ten controls who had not taken any drugs in the previous week. Tobramycin concentrations were measured in duplicate by the Emit assay modified to obtain precise results at concentrations greater than 0.25 microgram/ml. The drug was undetectable in 32 of 34 saliva specimens and only trace amounts were present in the other two, even though corresponding steady-state serum concentrations were greater than or equal to 4.0 micrograms/ml for 29 of 34 specimens. Tobramycin values were zero for all ten saliva specimens from controls. These results probably can be extrapolated to other aminoglycoside antibiotics since most are hydrophilic and ionized at physiologic pH, which disfavors penetration into saliva. We conclude that saliva cannot be used as a noninvasive indirect method of measuring aminoglycoside serum concentrations to guide dosage adjustments.

An enzymatic assay for monitoring serum, cerebrospinal fluid, and urine concentration of beta-lactam antibiotics

August 29/October 24, 1984 An enzymatic assay for the determination of the concentrations of various beta-lactam antibiotics in serum, urine, and cerebrospinal fluid samples is described. Recently developed beta-lactam derivatives are used as competitive inhibitors of the breakdown of the labile coloured beta-lactam compound PADAC, which serves as the substrate for the various beta-lactamases. Under the conditions of the assay, there is effectively no interference due to the matrix. Moreover, the assay is not influenced by other antibiotics such as aminoglycosides, macrolides, ansamycines, tetracyclines, fusidic acid or fosfomycin. The C.V.s for within-run precision ranged from 3.7% to 4.4%, depending on the beta-lactam derivative. The sensitivity of the assay is at least comparable with that of conventional procedures. Excellent correlations were observed between the enzymatic and the microbiological procedures; correlation coefficients: r = 0.988 for 22 imipenem samples, r = 0.968 for 16 cefotaxime samples, and r = 0.989 for 16 piperacillin samples routinely sent to our laboratory.

Comparison of the Beckman Auto ICS and the Syva Autolab 6000 for determination of gentamicin levels in serum

Two fully automated drug-monitoring systems, the Syva Autolab 6000 and the Beckman Auto ICS, were compared in terms of accuracy, precision, speed of operation, and cost effectiveness in the determination of gentamicin levels in serum. Within-run and between-run precision for both systems were acceptable (coefficient of variation, 2.0 to 6.9%), and patient sample comparisons resulted in an intermethod correlation coefficient of 0.96. When reference samples (prepared to contain 1.2 to 10 micrograms of gentamicin per ml) were assayed, the Syva Autolab 6000 obtained concentrations within 8% of expected values, whereas the Beckman Auto ICS reported values up to 17% higher than target values. In a time and cost comparison, reagent costs for the Beckman system were ca. 50% less than for the Syva Autolab 6000; the Syva system, however, determined patient results two to three times faster than the Beckman Auto ICS.

Analytical accuracy of determinations of aminoglycoside concentrations by enzyme multiplied immunoassay, fluorescence polarization immunoassay, and radioimmunoassay in the presence of heparin

The accuracy of gentamicin, netilmicin, and tobramycin concentration determinations by enzyme multiplied immunoassay technique (EMIT; Syva Corp., Palo Alto, Calif.), fluorescence polarization immunoassay (TDx; Abbott Diagnostics, Irving, Tex.), and radioimmunoassay were compared in the presence of 0 to 3,000 USP units of porcine heparin per ml. Gentamicin, netilmicin, and tobramycin concentrations determined by EMIT decreased by 10 and 50% in the presence of 75 and 1,000 USP units/ml, 2 and 5 USP units/ml, and 2 and 7.5 USP units/ml, respectively. Accuracy of the TDx and radioimmunoassay determinations, however, were not affected by the presence of heparin. Blood samples for the determination of gentamicin, netilmicin, and tobramycin by EMIT should not be collected in evacuated heparinized tubes.

Serum level monitoring of antibacterial drugs. A review

Serum concentration measurements of antibacterial agents are increasingly used to optimise drug dosage regimens. However, this approach is only justified for drugs with a low therapeutic index and poor predictability of serum concentrations, such as the aminoglycosides, chloramphenicol and vancomycin, whereas the penicillins and cephalosporins can safely be applied well above their minimum inhibitory concentrations. Wide interpatient variation in distribution and elimination are the main reasons for the unpredictability of aminoglycoside serum concentrations. It has been shown that in patients with normal creatinine clearance, the apparent elimination half-life of gentamicin varies from 0.4 to 7.6 hours. The pharmacokinetics of the aminoglycosides are most adequately described by a 3-compartment open model where the slow terminal half-life reflects elimination from the deep tissue compartment. The accumulation of the aminoglycosides in this compartment, which includes the kidneys and inner ear, is probably an important factor in their potential toxicity in these organs. Careful serum level monitoring may reduce, but cannot totally avoid, the risk of side effects. However, maintenance of effective drug levels appears to be at least an equally important goal of aminoglycoside serum level monitoring. Chloramphenicol is also a potentially toxic antibacterial agent. Its therapeutic range is usually considered to be 15 to 25 mg/L. The most important side effects are the 'grey baby syndrome' and bone marrow toxicity. Chloramphenicol is metabolised to several microbiologically inactive products. It also shows wide interpatient variability of its pharmacokinetics, especially in young children, and serum levels should therefore be followed in these patients. Vancomycin, a highly effective agent for staphylococcal and enterococcal infections, may also exhibit nephrotoxic and ototoxic side effects. A well-defined therapeutic range has not yet been established but in view of its minimum inhibitory concentrations it seems reasonable to maintain vancomycin serum concentrations between 15 and 50 mg/L. Since this drug is excreted unchanged in the urine, serum levels should particularly be monitored in patients with impaired renal function. The advances in routine therapeutic drug monitoring are directly related to rapid developments in technologies associated with the quantification of these agents. Microbiological plate diffusion assays are now often replaced by more specific immunoassays (radioimmunoassay, enzyme immunoassay, and fluorescence immunoassay) and chromatographic techniques.

Tobramycin serum level monitoring in young patients with normal renal function

Five clinical strategies for monitoring serum tobramycin concentrations were compared in a population of children and young adults with normal renal function receiving tobramycin for suspected sepsis. The drug monitoring strategies were evaluated on the basis of the ability of each to predict subsequent drug levels. The strategies included 3 methods requiring assessment of individual drug disposition: (a) measurement of peak drug concentrations after 2 separate doses; (b) a 3-point kinetic study to define distribution volume and elimination rate; (c) a 3-point kinetic study with adjustment of the value for elimination rate to account for deep compartment drug accumulation; and 2 strategies using a fixed-dose approach in which prediction of individual levels was made on the basis of mean population kinetic parameters. Although all methods were of similar accuracy, the fixed-dose strategy was the most precise in predicting subsequent serum tobramycin levels (95% tolerance limits = 84-135% of predicted). Poor performance of the other strategies was accounted for by interpatient variability of tobramycin disposition that was small relative to the intrapatient variability in these measurements. We conclude that these strategies for aminoglycoside serum level monitoring, which have proven beneficial in patients with impaired renal function, afford little benefit to children and young adults with normal renal function. Administration of these drugs on a fixed-dose schedule without serum concentration monitoring appears to be warranted in this select population. Alternatively, specific strategies for this population must be developed that consider the small interindividual differences in drug disposition and low incidence of toxicity.

Antibiotic trials in intra-abdominal infections. A critical evaluation of study design and outcome reporting

The introduction of several new antibiotics, including cephalosporins and ureido-penicillins, has been a stimulus for clinical trials with these agents for intra-abdominal infection. Despite marked differences in antibacterial spectra, substantial differences in treatment results have not been documented. We reviewed published trials of antibiotic therapy for intra-abdominal infection to determine factors in study design that might impair identification of clinically important differences between regimens. Sixteen articles were identified that provided sufficient numbers of cases and data for analysis. Eight were prospective comparative trials, the remainder "single-armed" studies. The mortality rate was 3.5%, and the overall success rate was 84% for aminoglycoside plus clindamycin (range 52%-96%), 89% (range 83%-93%) for aminoglycoside plus metronidazole, and 93% (range 61%-95%) for cephalosporin-based regimens. Several defects in study design were identified. (1) Exclusionary criteria employed generally prevented enrollment of seriously ill patients or infections associated with high failure rates: Patients were excluded if even mild renal impairment was present or if antibiotic therapy had been recently administered, thereby excluding patients with postoperative or recurrent infections. Several studies allowed entry of contaminated but not infected patients. (2) Criteria used for reporting infectious diagnosis, premorbid health status, severity of infection, and outcome were nonuniform, and few studies provided such information. (3) Despite the small number of treatment failures, data reported did not allow determination of the basis for failure. For example, only four studies provided information on the operations performed upon treatment failures. Whether treatment failures were due to inadequate antibiotic therapy could therefore not be determined. Enrollment of a variety of low mortality infections precluded demonstration of any differences in regimens. Use of stratified randomization, stratifying for site of infection and severity of infection, and inclusion of greater numbers of patients would increase the likelihood of identifying differences between regimens. Such study design would likely require a multicenter trial to enroll sufficient numbers of cases for statistical analysis.