Bone penetration of amoxicillin and clavulanic acid evaluated by population pharmacokinetics and Monte Carlo simulation

Penicillin concentrations in bone and subcutaneous tissue: A porcine microdialysis study comparing oral and intravenous treatment

Penicillin is available in both an oral (penicillin V) and intravenous formulation (penicillin G), theoretically allowing for a safe transition between the two. However, the use of oral penicillin remains a topic of debate due to low and variable bioavailability. This study aimed to assess the time for which the free penicillin concentration exceeded targeted minimum inhibitory concentrations for Staphylococcus aureus and Streptococcus species (0.125, 0.25, and 0.5 mg/L) in cancellous bone and subcutaneous tissue after intravenous penicillin and oral penicillin administration. 12 female pigs (68-75 kg) were assigned, according to local standard clinical regimes, to either intravenous penicillin (1.2 g) or oral penicillin (0.8 g) treatment every 6 h over an 18 h period. Microdialysis catheters were placed for sampling in tibial cancellous bone and adjacent subcutaneous tissue. Data was dynamic/continually collected in the first dosing interval (0-6 h), simulating a prophylactic situation, and the third dosing interval (12-18 h), simulating a therapeutic setting. Plasma samples were collected for reference. For all investigated targets, intravenous treatment resulted in a longer mean time above relevant minimum inhibitory concentrations in cancellous bone during the first dosing interval, and in both cancellous bone and subcutaneous tissue during the third dosing interval compared to oral treatment. With clinically relevant dosing, intravenous penicillin provides superior exposure compared to oral penicillin in both a prophylactic and therapeutic setting.

Population pharmacokinetics and humanized dosage regimens matching the peak, area, trough, and range of amikacin plasma concentrations in immune-competent murine bloodstream and lung infection models

Amikacin is an FDA-approved aminoglycoside antibiotic that is commonly used. However, validated dosage regimens that achieve clinically relevant exposure profiles in mice are lacking. We aimed to design and validate humanized dosage regimens for amikacin in immune-competent murine bloodstream and lung infection models of Acinetobacter baumannii. Plasma and lung epithelial lining fluid (ELF) concentrations after single subcutaneous doses of 1.37, 13.7, and 137 mg/kg of body weight were simultaneously modeled via population pharmacokinetics. Then, humanized amikacin dosage regimens in mice were designed and prospectively validated to match the peak, area, trough, and range of plasma concentration profiles in critically ill patients (clinical dose: 25-30 mg/kg of body weight). The pharmacokinetics of amikacin were linear, with a clearance of 9.93 mL/h in both infection models after a single dose. However, the volume of distribution differed between models, resulting in an elimination half-life of 48 min for the bloodstream and 36 min for the lung model. The drug exposure in ELF was 72.7% compared to that in plasma. After multiple q6h dosing, clearance decreased by ~80% from the first (7.35 mL/h) to the last two dosing intervals (~1.50 mL/h) in the bloodstream model. Likewise, clearance decreased by 41% from 7.44 to 4.39 mL/h in the lung model. The humanized dosage regimens were 117 mg/kg of body weight/day in mice [administered in four fractions 6 h apart (q6h): 61.9%, 18.6%, 11.3%, and 8.21% of total dose] for the bloodstream and 96.7 mg/kg of body weight/day (given q6h as 65.1%, 16.9%, 10.5%, and 7.41%) for the lung model. These validated humanized dosage regimens and population pharmacokinetic models support translational studies with clinically relevant amikacin exposure profiles.

Improved characterization of aminoglycoside penetration into human lung epithelial lining fluid via population pharmacokinetics

Aminoglycosides are important treatment options for serious lung infections, but modeling analyses to quantify their human lung epithelial lining fluid (ELF) penetration are lacking. We estimated the extent and rate of penetration for five aminoglycosides via population pharmacokinetics from eight published studies. The area under the curve in ELF vs plasma ranged from 50% to 100% and equilibration half-lives from 0.61 to 5.80 h, indicating extensive system hysteresis. Aminoglycoside ELF peak concentrations were blunted, but overall exposures were moderately high.

Facts and trends in dental antibiotic and analgesic prescriptions in Germany, 2012-2021

OBJECTIVES

The study aims to overview German dentists' development of antibiotic and analgesic prescriptions from 2012 to 2021.

MATERIALS AND METHODS

A longitudinal database analysis was performed based on the annual reports of the "Research Institute for Local Health Care Systems" (WIdO, Berlin).

RESULTS

From 2012 until 2021, dental antibiotic prescriptions fell by 17.9%. In contrast, the dental proportion of antibiotic prescriptions compared to all antibiotic prescriptions in Germany increased from 9.1 to 13.6%. Aminopenicillins enhanced their share from 35.6 to 49.4%, while clindamycin prescriptions declined from 37.8 to 23.4%. The proportion of ibuprofen prescriptions significantly increased from 60.4% in 2012 to 79.0% in 2021.

CONCLUSIONS

Since 2013, the most frequently prescribed antibiotic by German dentists has been amoxicillin reaching nearly half of all dental antibiotic prescriptions in 2021. Simultaneously, the proportion of clindamycin has steadily decreased, but the level is still high compared to international data. During the past decade, ibuprofen as a first-line analgesic in German dentistry was continuously gaining in importance.

CLINICAL RELEVANCE

Aminopenicillins have the best risk-benefit balance in dentistry, but the use of antibiotics generally must be limited only to cases of severe infections or compromised patients. Pre-existing diseases or permanent medications should always be considered when choosing an analgesic.

Infective Costochondritis after Augmentation Mammoplasty: A Rare Case Report and Review of the Literature

Silicone breast implant insertion is a commonly performed surgical procedure for breast augmentation or reconstruction. Among various postoperative complications, infection is one of the main causes of patient readmission and may ultimately require explantation. We report a case of infective costochondritis after augmentation mammoplasty, which has rarely been reported and is therefore difficult to diagnose. A 36-year-old female visited the clinic for persistent redness, pain, and purulent discharge around the left anteromedial chest, even after breast implant explantation. Magnetic resonance imaging showed abscess formation encircling the left fourth rib and intracartilaginous and bone marrow signal alteration at the left body of the sternum and left fourth rib. En bloc resection of partial rib and adjacent sternum were done and biopsy results confirmed infective costochondritis. Ten months postoperatively, the patient underwent chest wall reconstruction with an artificial bone graft and acellular dermal matrix. As shown in this case, early and aggressive surgical debridement of the infected costal cartilage and sternum should be performed for infective costochondritis. Furthermore, delayed chest wall reconstruction could significantly contribute to the quality of life.

Individual Components of Polymyxin B Modeled via Population Pharmacokinetics to Design Humanized Dosage Regimens for a Bloodstream and Lung Infection Model in Immune-Competent Mice

Polymyxin B is a "last-line-of-defense" antibiotic approved in the 1960s. However, the population pharmacokinetics (PK) of its four main components has not been reported in infected mice. We aimed to determine the PK of polymyxin B1, B1-Ile, B2, and B3 in a murine bloodstream and lung infection model of Acinetobacter baumannii and develop humanized dosage regimens. A linear 1-compartment model, plus an epithelial lining fluid (ELF) compartment for the lung model, best described the PK. Clearance and volume of distribution were similar among the four components. The bioavailability fractions were 72.6% for polymyxin B1, 12.0% for B1-Ile, 11.5% for B2, and 3.81% for B3 for the lung model and were similar for the bloodstream model. While the volume of distribution was comparable between both models (17.3 mL for the lung and ~27 mL for the bloodstream model), clearance was considerably smaller for the lung (2.85 mL/h) compared to that of the bloodstream model (5.59 mL/h). The total drug exposure (AUC) in ELF was high due to the saturable binding of polymyxin B presumably to bacterial lipopolysaccharides. However, the modeled unbound AUC in ELF was ~16.7% compared to the total drug AUC in plasma. The long elimination half-life (~4 h) of polymyxin B enabled humanized dosage regimens with every 12 h dosing in mice. Daily doses that optimally matched the range of drug concentrations observed in patients were 21 mg/kg for the bloodstream and 13 mg/kg for the lung model. These dosage regimens and population PK models support translational studies for polymyxin B at clinically relevant drug exposures.

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review—Part I

The challenging severity of some infections, especially in critically ill patients, makes the diffusion of antimicrobial drugs within tissues one of the cornerstones of chemotherapy. The knowledge of how antibacterial agents penetrate tissues may come from different sources: preclinical studies in animal models, phase I–III clinical trials and post-registration studies. However, the particular physiopathology of critically ill patients may significantly alter drug pharmacokinetics. Indeed, changes in interstitial volumes (the third space) and/or in glomerular filtration ratio may influence the achievement of bactericidal concentrations in peripheral compartments, while inflammation can alter the systemic distribution of some drugs. On the contrary, other antibacterial agents may reach high and effective concentrations thanks to the increased tissue accumulation of macrophages and neutrophils. Therefore, the present review explores the tissue distribution of beta-lactams and other antimicrobials acting on the cell wall and cytoplasmic membrane of bacteria in critically ill patients. A systematic search of articles was performed according to PRISMA guidelines, and tissue/plasma penetration ratios were collected. Results showed a highly variable passage of drugs within tissues, while large interindividual variability may represent a hurdle which must be overcome to achieve therapeutic concentrations in some compartments. To solve that issue, off-label dosing regimens could represent an effective solution in particular conditions.

The mysteries of target site concentrations of antibiotics in bone and joint infections: what is known? A narrative review

INTRODUCTION

Currently, antibiotic treatment is often a standard dosing regimen in bone and joint infections (BJI). However, it remains unknown if exposure at the target-site is adequate. The aim of this review is to gain more insight in the relationship between the target site concentration of antibiotic and the minimal inhibitory concentration to target the bacteria in bone and joint infections (BJI).

AREAS COVERED

A literature search was performed by Erasmus MC Medical library. Bone, bone tissue and synovial concentration of antibiotics were covered in humans. In addition, we reported number of patients, dose, sampling method, analytical method and tissue and plasma concentrations. We used the epidemiological cut-off value (ECOFF) values of the targeted micro-organisms. If more than 3 publications were available on the antibiotic, we graphically presented ECOFFS values against reported antibiotic concentrations.

EXPERT OPINION

For most antibiotics the literature is sparse. In addition, a lot of variable and total antibiotic concentrations are published. Ciprofloxacin, cefazolin, cefuroxime, vancomycin and linezolid seem to have adequate average exposure if correlating total concentration to ECOFF, when standard dosing is used. With regards to other antibiotics, results are inconclusive. More extensive pharmacokinetic/pharmacodynamic modeling in BJI is needed.

Development and validation of a dosing nomogram for amoxicillin in infective endocarditis

BACKGROUND

Amoxicillin is the first-line treatment for streptococcal or enterococcal infective endocarditis (IE) with a dose regimen adapted to weight.

OBJECTIVES

Covariates influencing pharmacokinetics (PK) of amoxicillin were identified in order to develop a dosing nomogram based on identified covariates for individual adaptation.

PATIENTS AND METHODS

Patients treated with amoxicillin administered by continuous infusion for IE were included retrospectively. The population PK analysis was performed using the Pmetrics package for R (NPAG algorithm). Influence of weight, ideal weight, height, BMI, body surface area, glomerular filtration rate adapted to the body surface area and calculated by the CKD-EPI method (mL/min), additional ceftriaxone treatment and serum protein level on amoxicillin PK was tested. A nomogram was then developed to determine the daily dose needed to achieve a steady-state free plasma concentration above 4× MIC, 100% of the time, without exceeding a total plasma concentration of 80 mg/L.

RESULTS

A total of 160 patients were included. Population PK analysis was performed on 540 amoxicillin plasma concentrations. A two-compartment model best described amoxicillin PK and the glomerular filtration rate covariate significantly improved the model when included in the calculation of the elimination constant Ke.

CONCLUSIONS

This work allowed the development of a dosing nomogram that can help to increase achievement of the PK/pharmacodynamic targets in IE treated with amoxicillin.

Are Oral Antibiotics an Effective Alternative to Intravenous Antibiotics in Treatment of Osteomyelitis of the Jaw?

PURPOSE

To review treatment of osteomyelitis of the jaw (OMJ) and determine whether antibiotic route and/or length of administration impacts resolution of infection postsurgically.

METHODS

The investigators designed a retrospective cohort study enrolling a sample of patients treated at Harborview Medical Center from January 1, 2009 to December 31, 2019. The primary predictor variable was antibiotic administration route: oral (PO) only, intravenous (IV) only, IV transitioned to PO (IV + PO), or none. The secondary predictor was duration of antibiotic therapy (≤6 weeks or >6 weeks). The primary outcome variable was resolution of infection at 2 months follow-up posttreatment completion. The secondary outcome variable was number of surgeries to resolution of infection. Descriptive, bivariate, and multiple linear regression statistics were computed, with statistical significance set at P < .05.

RESULTS

Sixty-seven individuals met inclusion criteria (38 male), mean age 51 years (18 to 88). Forty-nine (73%) received PO antibiotics, 12 (18%) IV + PO, 3 (4%) IV, and 3 (4%) none. Both PO and IV antibiotics were associated with clinical resolution (P = .022, .005, respectively) compared with debridement alone. Antibiotic duration of ≤6 weeks compared with >6 weeks was not significant. Seventy-six percent (51 of 67) required only 1 surgery. In the multivariate logistic regression, PO was associated with clinical resolution (P = .025, OR = 5.05). Penicillin allergy (P = 0.049, OR = 0.223) and diabetes (P = .008, OR = 0.104) were adversely associated with outcome.

CONCLUSIONS

OMJ was successfully treated with oral antibiotics and surgery. Prescribing 6 weeks of IV antibiotics may be antiquated. Clinicians should consider oral penicillins as first line whenever possible. Further studies are recommended.

Concentration of Penicillin G in Jawbone Affected by Antiresorptive Agent-Related Osteonecrosis Following a Single Preoperative Dose

The aim of this study was to evaluate the concentration of penicillin G in bone affected by antiresorptive agent-related osteonecrosis of the jaw (ARONJ) following a single preoperative dose of 10 million international units (6000 mg). ARONJ is a major concern in patients administered antiresorptive agents for conditions associated with pathologically increased bone resorption. Antibiotic therapy is a key component of most treatment approaches for ARONJ and penicillin based regimens, providing a cost effective therapy option with a favorable side effect profile, are administered most frequently. In this study, high performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) was applied to evaluate penicillin G concentration in serum and bone samples of 19 patients suffering from ARONJ and undergoing surgical treatment under perioperative intravenous (IV) antibiotic therapy. Penicillin G bone concentrations were above the limit of detection (0.1 μg/g bone tissue) in 16 out of 19 samples, with a median concentration of 2.7 μg/g (range 0.1–8.8 μg/g). Penicillin G concentrations in intraoperative serum samples were above the limit of detection in all serum samples, with a median concentration of 116 μg/mL (range 1–232 μg/mL). Thus, considering bacteria frequently found in ARONJ lesions, penicillin G at levels providing adequate antimicrobial activity was detected in the serum and 16 out of 19 osteonecrotic lesions of patients suffering from ARONJ.

Physiologically Based Population Pharmacokinetic Modeling Approach for Ciprofloxacin in Bone of Patients Undergoing Orthopedic Surgery

Ciprofloxacin is highly active against bacteria that commonly cause bone infections. However, the time-course of ciprofloxacin in bone has not been characterized using population pharmacokinetic modeling. Thirty-nine patients received a 1-h infusion of 400 mg of ciprofloxacin before orthopedic surgery. Blood and bone samples were collected at 0.5 to 20 h following the start of the infusion. Bone samples were separated into cortical and cancellous bone and pulverized under liquid nitrogen using a cryogenic mill. Ciprofloxacin in plasma, and cortical and cancellous bone was quantified by liquid chromatography-tandem mass spectrometry. A physiologically based pharmacokinetic modeling approach was utilized to describe the concentration-time profiles in plasma and bone. Ciprofloxacin concentrations ranged from 0.176 to 5.98 mg/L (median, 1.67; density, 1.99 g/cm³) in cortical, and 0.224 to 14.6 mg/L (median, 1.22; 1.92 g/cm³) in cancellous bone. The average observed cortical bone/plasma concentration ratio was 0.67 at 0.5 to 2 h (n = 7) and 5.1 at 13 to 20 h (n = 9). For cancellous bone the respective average ratios were 0.77 and 4.4. The population PK model included a central (blood) compartment, two peripheral tissue compartments, and compartments for the organic and inorganic (hydroxyapatite) matrix in cortical and cancellous bone. The population mean ciprofloxacin clearance was 20.7 L/h. The estimated partition coefficients of the organic bone matrix were 3.39 for cortical and 5.11 for cancellous bone. Ciprofloxacin achieved higher concentrations in bone than plasma. Slow redistribution from bone to plasma may have been due to binding to the inorganic bone matrix. The developed model presents a step toward optimized antibiotic dosing in osteomyelitis.

Oral amoxicillin-clavulanate for treating diabetic foot infections

AIM

To assess amoxicillin-clavulanate (AMC) for the oral therapy of diabetic foot infections (DFIs), especially for diabetic foot osteomyelitis (DFO).

METHODS

We performed a retrospective cohort analysis among 794 DFI episodes, including 339 DFO cases.

RESULTS

The median duration of antibiotic therapy after surgical debridement (including partial amputation) was 30 days (DFO, 30 days). Oral AMC was prescribed for a median of 20 days (interquartile range, 12-30 days). The median ratio of oral AMC among the entire antibiotic treatment was 0.9 (interquartile range, 0.7-1.0). After a median follow-up of 3.3 years, 178 DFIs (22%) overall recurred (DFO, 75; 22%). Overall, oral AMC led to 74% remission compared with 79% with other regimens (χ² -test; P = 0.15). In multivariate analyses and stratified subgroup analyses, oral AMC resulted in similar clinical outcomes to other antimicrobial regimens, when used orally from the start, after an initial parenteral therapy, or when prescribed for DFO.

CONCLUSIONS

Oral AMC is a reasonable option when treating patients with DFIs and DFOs.

Bone and Joint Tissue Penetration of the Staphylococcus-Selective Antibiotic Afabicin in Patients Undergoing Elective Hip Replacement Surgery

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono (Debio 1452, AFN-1252), a novel antibiotic in development which targets the staphylococcal enoyl-acyl carrier protein reductase (FabI) and exhibits selective potent antibacterial activity against staphylococcal species, including methicillin-resistant Staphylococcus aureus. As part of clinical development in bone and joint infections, a distribution study in bone was performed in 17 patients who underwent elective hip replacement surgery.

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono (Debio 1452, AFN-1252), a novel antibiotic in development which targets the staphylococcal enoyl-acyl carrier protein reductase (FabI) and exhibits selective potent antibacterial activity against staphylococcal species, including methicillin-resistant Staphylococcus aureus. As part of clinical development in bone and joint infections, a distribution study in bone was performed in 17 patients who underwent elective hip replacement surgery. Patients received 3 doses of 240 mg afabicin orally (every 12 h) at various time points before surgery. Afabicin desphosphono concentrations were measured by liquid chromatography-tandem mass spectrometry in plasma, cortical bone, cancellous bone, bone marrow, soft tissue, and synovial fluid collected during surgery at 2, 4, 6, or 12 h after the third afabicin dose. The study showed good penetration of afabicin desphosphono into bone tissues, with mean area under the curve ratios for cortical bone-, cancellous bone-, bone marrow-, soft tissue-, and synovial fluid-to-total plasma concentrations of 0.21, 0.40, 0.32, 0.35, and 0.61, respectively. When accounting for the free fraction in plasma (2%) and synovial fluid (9.4%), the mean ratio was 2.88, which is indicative of excellent penetration and which showed that the afabicin desphosphono concentration was beyond the MIC₉₀ of S. aureus over the complete dosing interval. These findings, along with preclinical efficacy data, clinical efficacy data for skin and soft tissue staphylococcal infection, the availability of both intravenous and oral formulations, and potential advantages over broad-spectrum antibiotics for the treatment of staphylococcal bone or joint infections, support the clinical development of afabicin for bone and joint infections. (This study has been registered at ClinicalTrials.gov under identifier NCT02726438.)

Population Pharmacokinetic Study of Amoxicillin-Treated Burn Patients Hospitalized at a Swiss Tertiary-Care Center

The objective of this study was to investigate the population pharmacokinetics (PK) of amoxicillin in ICU burn patients and the optimal dosage regimens. This was a prospective study involving 21 consecutive burn patients receiving amoxicillin. PK data were analyzed using nonlinear mixed-effects modeling. Monte-Carlo simulations assessed the influence of various amoxicillin dosage regimens with identified covariates on the probability to achieve a target (PTA) value of time during which free amoxicillin concentrations in plasma exceeded the MIC (fT>MIC). A two-compartment model best described the data. Creatinine clearance (CL_CR) and body weight (BW) influenced amoxicillin CL and central volume of distribution (V₁), respectively. The median CL_CR (Cockcroft-Gault formula) was high (128 ml/min), with 25% of patients having CL_CRs of >150 ml/min. The CL, V₁, and half-life (t_1/2) values at steady state for a patient with a CL_CR of 110 ml/min and BW of 70 kg were 13.6 liters/h, 9.7 liters, and 0.8 h, respectively. Simulations showed that a target fT>MIC of ≥50% was achieved (PTA > 90%) with standard amoxicillin dosage regimens (1 to 2 g every 6 to 8 h [q6-8h]) when the MIC was low (<1 mg/liter). However, increased dosages of up to 2 g/4 h were necessary in patients with augmented CL_Rs or higher MICs. Prolonging amoxicillin infusion from 30 min to 2 h had a favorable effect on target attainment. In conclusion, this population analysis shows an increased amoxicillin CL and substantial CL PK variability in burn patients compared to literature data with nonburn patients. Situations of augmented CL_CR and/or high bacterial MIC target values may require dosage increases and longer infusion durations. (This study has been registered at ClinicalTrials.gov under identifier NCT01965340.).

Determination and identification of antibiotic-resistant oral streptococci isolated from active dental infections in adults

OBJECTIVE

To determine and identify antibiotic-resistant bacteria (ARB) of oral streptococci from active dental infections in adults and its association with age and gender.

MATERIAL AND METHODS

This cross-sectional study included 59 subjects from 18 to 62 years old. Ninety-eighth samples obtained from the subjects were cultivated in agar plates containing antibiotics amoxicillin/clavulanic acid (A-CA), clindamycin, and moxifloxacin (concentrations of 16, 32 or 64 µg/ml). PCR assay was performed to identify bacterial species.

RESULTS

The bacterial species that showed more antibiotic-resistance (AR) was S. mutans (45.9%), followed by S. gordonii (21.6%), S. oralis (17.6%), S. sanguinis (9.5%), S. salivarius (5.4%) and S. sobrinus (0%). Moreover, clindamycin (59.4%) showed the highest frequency of AR. Moxifloxacin and A-CA showed an susceptibility >99.1%, while clindamycin showed the lowest efficacy (93.3%); there was a significant statistically difference (p < .01). The age group between 26 and 50 years old (32.2%) and females (28.8%) showed more multiresistance. Clindamycin showed a statistical difference (p < .05) when comparing groups by gender.

CONCLUSIONS

Clindamycin was the antibiotic with the highest frequency of ARB and lower bactericidal effect. Moxifloxacin and A-CA showed the highest efficacy and the lowest ARB frequency. Streptococcus mutans was the bacterial specie that showed an increased frequency of AR.

Survey of systemic antimicrobial prescribing for dogs by Victorian veterinarians

OBJECTIVE

Investigate the current antimicrobial prescribing patterns of veterinarians in Victoria for dogs and compare these results to patterns described 20 years ago.

METHODS

A questionnaire was sent to 1380 veterinarians in Victoria. The first section collected demographic information of respondents. The second and third sections evaluated respondents' approach to use of antimicrobial drugs for scenarios in dogs in which 'clinical evidence suggests bacterial infection is the likely cause' and where 'it is unknown whether bacterial infection plays a role'. The final section evaluated respondents' approach to use of antimicrobial drugs during dental extraction in a dog.

RESULTS

Of the 1380 veterinarians who were contacted, 259 responses were received (response rate 19%). Of these respondents, 95% (246/259) completed their veterinary degree at the University of Melbourne. The ratio of female to male respondents was 2.1 : 1 (171 : 82) and of urban to rural respondents was 1.9 : 1 (159 : 85). Drug selection for some scenarios was open to criticism. For example, to treat chronic prostatitis 16% (42/259) of respondents selected amoxicillin-clavulanate even though it has poor penetration of prostatic tissues. Some prescribing choices have changed since 1997; for example, for acute tracheobronchitis, 36% (73/204) of respondents indicated they would use antimicrobials, compared with 87% of respondents in 1997. For the treatment of idiopathic vestibular disease, only 5% (10/197) of respondents in the current study versus 45% (294/654) in the 1997 survey opted to use antimicrobials.

CONCLUSION

Antimicrobial drug selection for treatment of dogs by registered veterinarians in Victoria was generally consistent with recent recommendations, although some details were widely variable.

Population Pharmacokinetics and Target Attainment of Ertapenem in Plasma and Tissue Assessed via Microdialysis in Morbidly Obese Patients after Laparoscopic Visceral Surgery

Ertapenem provides broad-spectrum activity against many pathogens, and its use is relevant for the prophylaxis and treatment of infections in morbidly obese patients undergoing surgery. However, its pharmacokinetics and tissue penetration in these patients are not well defined. We assessed the population pharmacokinetics and target attainment for ertapenem in the plasma, subcutaneous tissue, and peritoneal fluid of morbidly obese patients. Six female patients (body mass index, 43.7 to 55.9 kg/m²) received 1,000 mg ertapenem as 15-min infusions at 0 and 26 h. On day 2, the unbound ertapenem concentrations in plasma, subcutaneous tissue, and peritoneal fluid were measured by microdialysis; total plasma concentrations were additionally quantified. The probability of attaining a target of an unbound ertapenem concentration above the MIC for at least 40% of the dosing interval was predicted via Monte Carlo simulations. The population pharmacokinetic model contained two disposition compartments and simultaneously described all concentrations. For unbound ertapenem, total clearance was 12.3 liters/h (coefficient of variation, 21.6% for between-patient variability) and the volume of distribution at steady state was 57.8 liters in patients with a 53-kg fat-free mass. The area under the concentration-time curve (AUC) for ertapenem was 49% lower in subcutaneous tissue and 25% lower in peritoneal fluid than the unbound AUC in plasma. Tissue penetration was rapid (equilibration half-life, <15 min) and was variable in subcutaneous tissue. Short-term ertapenem infusions (1,000 mg every 24 h) achieved robust (>90%) target attainment probabilities for MICs of up to 1 mg/liter in plasma, 0.25 to 0.5 mg/liter in subcutaneous tissue, and 0.5 mg/liter in peritoneal fluid. Ertapenem presents an attractive choice for many pathogens relevant to morbidly obese patients undergoing surgery. (This study has been registered at ClinicalTrials.gov under identifier NCT01407965.).

Population Pharmacokinetics and Target Attainment of Meropenem in Plasma and Tissue of Morbidly Obese Patients after Laparoscopic Intraperitoneal Surgery

Meropenem serves as a clinically important, broad-spectrum antibiotic. While meropenem is commonly used in obese patients, its pharmacokinetics in this patient group is not well known. Our aim was to characterize the population pharmacokinetics and target attainment in plasma, subcutaneous tissue, and peritoneal fluid for meropenem in morbidly obese patients. Four doses of 1g meropenem were given as 15-min infusions every 8 h to five morbidly obese patients (body mass index [BMI], 47.6 to 62.3 kg/m(2)). After the fourth dose, serial meropenem concentrations were determined in plasma and, via microdialysis, in subcutaneous tissue and peritoneal fluid. All concentrations were analyzed simultaneously via population modeling, and target attainment probabilities predicted via Monte Carlo simulations using the target of unbound meropenem concentrations above the MIC for at least 40% of the dosing interval. For patients with 53 kg fat-free mass, total clearance was 18.7 liters/h and volume of distribution at steady state was 27.6 liters. The concentrations in subcutaneous tissue and peritoneal fluid largely paralleled those in plasma (equilibration half-life, <30 min). The area under the curve (AUC) in subcutaneous tissue divided by the plasma AUC had a mean of 0.721. For peritoneal fluid, this AUC ratio had a mean of 0.943. Target attainment probabilities were >90% after 1 g meropenem every 8 h as a 15-min infusion for MICs of up to 2 mg/liter in plasma and peritoneal fluid and 0.5 mg/liter in subcutaneous tissue. Meropenem pharmacokinetics in plasma and peritoneal fluid of obese patients was predictable, but subcutaneous tissue penetration varied greatly. (This study has been registered at ClinicalTrials.gov under registration no. NCT01407965.).

Heparinized nanohydroxyapatite/collagen granules for controlled release of vancomycin

The purpose of this study was to develop a bone substitute material capable of preventing or treating osteomyelitis through a sustainable release of vancomycin and simultaneously inducing bone regeneration. Porous heparinized nanohydroxyapatite (nanoHA)/collagen granules were characterized using scanning electron microscopy, micro-computed tomography and attenuated total reflectance Fourier transform infrared spectroscopy. After vancomycin adsorption onto the granules, its releasing profile was studied by UV molecular absorption spectroscopy. The heparinized granules presented a more sustainable release over time, in comparison with nonheparinized nanoHA and nanoHA/collagen granules. Vancomycin was released for 360 h and proved to be bioactive until 216 h. Staphylococcus aureus adhesion was higher on granules containing collagen, guiding the bacteria to the material with antibiotic, improving their eradication. Moreover, cytotoxicity of the released vancomycin was assessed using osteoblast cultures, and after 14 days of culture in the presence of vancomycin, cells were able to remain viable, increasing their metabolic activity and colonizing the granules, as observed by scanning electron microscopy and confocal laser scanning microscopy. These findings suggest that heparinized nanoHA/collagen granules are a promising material to improve the treatment of osteomyelitis, as they are capable of releasing vancomycin, eliminating the bacteria, and presented morphological and chemical characteristics to induce bone regeneration.

Molecular identification and antibiotic resistant bacteria isolated from primary dentition infections

BACKGROUND

Bacterial resistance to antibiotics is a health problem in many parts of the world. The aim of this study was to identify bacteria from dental infections and determine bacterial resistance to antibiotics used in dental care in the primary dentition.

METHODS

This cross-sectional study comprised 60 children who presented for dental treatment for active dental infections in the primary dentition. Samples from dental infections were collected and bacteria were identified by polymerase chain reaction (PCR) assay. Bacterial resistance to antibiotics was determined by colony forming units on agar plates containing amoxicillin, clindamycin and amoxillicin-clavulanic acid (A-CA) tested at 8 μg/ml or 16 μg/ml.

RESULTS

Clindamycin in both concentrations tested (8 μg/ml and 16 μg/ml) showed the highest bacterial resistance (85.9%), followed by amoxicillin (43.7%) and A-CA (12.0%). All comparisons among the three antibiotics used in the study exhibited statistical significance (p = <0.05) in both concentrations tested (8 μg/ml and 16 μg/ml), and under aerobic and anaerobic conditions. The most prevalent resistant species identified by PCR in primary dentition infections were: Streptococcus oralis and Prevotella intermedia (75.0%); Treponema denticola and Porphyromonas gingivalis (48.3%); Streptococcus mutans (45.0%); Campylobacter rectus; and Streptococcus salivarius (40%).

CONCLUSIONS

This study demonstrated that A-CA exhibited the lowest bacterial resistance for clinical isolates in primary dentition infections.

Concentrations of amoxicillin and clindamycin in teeth following a single dose of oral medication

OBJECTIVES

The main purpose of this study is the detection of amoxicillin and clindamycin concentrations in teeth.

MATERIALS AND METHODS

Eleven patients received 2 g of amoxicillin, and 11 patients received 600 mg of clindamycin in a single dose of oral medication at least 60 min prior to tooth extraction due to systemic diseases. The concentrations were determined in crowns and roots separately using liquid chromatography-tandem mass spectrometry (LC-MS-MS).

RESULTS

Amoxicillin (13 samples) and clindamycin (12 samples) were detected in the samples of the root and crown preparations of the extracted teeth. The mean concentration of amoxicillin was 0.502 μg/g in the roots and 0.171 μg/g in the crowns. The mean concentration of clindamycin was 0.270 μg/g in the roots and 0.064 μg/g in the crowns.

CONCLUSIONS

A single dose of oral amoxicillin and clindamycin leads to concentrations of both antibiotics in teeth which exceed the minimal inhibition concentration of some oral bacteria.

CLINICAL RELEVANCE

The proof of antibacterial activity in dental hard tissue after oral single-dose application is new. The antimicrobial effect of amoxicillin and clindamycin concentrations in roots of teeth may be of clinical relevance to bacterial reinfection from dentinal tubules.

Attenuation of colistin bactericidal activity by high inoculum of Pseudomonas aeruginosa characterized by a new mechanism-based population pharmacodynamic model

Colistin is increasingly being utilized against Gram-negative pathogens, including Pseudomonas aeruginosa, resistant to all other antibiotics. Since limited data exist regarding killing by colistin at different initial inocula (CFUo), we evaluated killing of Pseudomonas aeruginosa by colistin at several CFUo and developed a mechanism-based mathematical model accommodating a range of CFUo. In vitro time-kill experiments were performed using >or=8 concentrations up to 64 x the MIC of colistin against P. aeruginosa PAO1 and two clinical P. aeruginosa isolates at CFUo of 10(6), 10(8), and 10(9) CFU/ml. Serial samples up to 24 h were simultaneously modeled in the NONMEM VI (results shown) and S-ADAPT software programs. The mathematical model was prospectively "validated" by additional time-kill studies assessing the effect of Ca(2+) and Mg(2+) on killing of PAO1 by colistin. Against PAO1, killing of the susceptible population was 23-fold slower at the 10(9) CFUo and 6-fold slower at the 10(8) CFUo than at the 10(6) CFUo. The model comprised three populations with different second-order killing rate constants (5.72, 0.369, and 0.00210 liters/h/mg). Bacteria were assumed to release signal molecules stimulating a phenotypic change that inhibits killing. The proposed mechanism-based model had a good predictive performance, could describe killing by colistin for all three studied strains and for two literature studies, and performed well in a prospective validation with various concentrations of Ca(2+) and Mg(2+). The extent and rate of killing of P. aeruginosa by colistin were markedly decreased at high CFUo compared to those at low CFUo. This was well described by a mechanism-based mathematical model, which should be further validated using dynamic in vitro models.